Peronia peronii (Cuvier, 1804)

Dayrat, Benoit, Goulding, Tricia C., Apte, Deepak, Aslam, Sadar, Bourke, Adam, Comendador, Joseph, Khalil, Munawar, Ngo, Xuan Qu ảng, Tan, Siong Kiat & Tan, Shau Hwai, 2020, Systematic revision of the genus Peronia Fleming, 1822 (Gastropoda, Euthyneura, Pulmonata, Onchidiidae), ZooKeys 972, pp. 1-224 : 1

Peronia peronii (Cuvier, 1804) Figs 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16

Onchidium peronii Cuvier, 1804: 37-51, pl. 6, figs 1-9; Cuvier 1816: 411; Lamarck 1822: 46; Cuvier 1830: 46; Voigt 1834: 101; Deshayes 1836-1845: pl. 26, fig. 2; Deshayes and Milne-Edwards 1836: 709; JE Gray 1850: 117; ME Gray 1850: pl. 181, fig. 7; Berge 1855: 124, pl. 16, fig. 8; Plate 1893: 172-173, pl. 12, figs 85, 87, 91; Odhner 1919: 42; Hoffmann 1928: 44-45, 71-72 [in part only].

Peronia peronii (Cuvier, 1804): Fleming 1822a: 574; Fleming 1822b: 463; Keferstein 1865a: pl. CIII, fig. 1; Labbé 1934a: 190-191 [in part only]; Marcus and Marcus 1960: 877; Marcus and Marcus 1970: 213 [in part only]; Dayrat et al. 2011: 428; White et al. 2011: 4.

Onchis peronii (Cuvier, 1804): Férussac 1822: xxxi.

Peronia mauritiana Blainville, 1824: 281; Adams and Adams 1855: 235.

Onchidium tonganum Quoy & Gaimard, 1832: 210-211, pl. 15, figs 17, 18; Semper 1880: 258-260, pl. XIX, figs 2, 9, pl. XXII, figs 1, 2, 10 [in part only]; Bergh 1884a: 142-148, pl. VI, fig. 19, pl. VII, figs 1-6.

Peronia tongana (Quoy & Gaimard, 1832): Oken 1834a: 287; JE Gray 1850: 117; ME Gray, 1850: pl. 182, fig. 1, as tongensis ; Adams and Adams 1855: 235, pl. LXXXI, fig. 3; Keferstein 1865a: pl. CII, fig. 20; Tapparone Canefri 1883: 214 [in part only]; Labbé 1934a: 191-192, figs 4-7 [in part only].

Onchidium punctatum Quoy & Gaimard, 1832: 215-216, pl. 15, figs 27, 28. Syn. nov.

Peronia punctata (Quoy & Gaimard, 1832): Oken 1834a: 287; JE Gray 1850: 117; ME Gray 1850: pl. 183, fig. 3; Adams and Adams 1855: 235; Chenu 1859: 474, fig. 3505; Tapparone Canefri 1883: 214.

Onchidium melanopneumon Bergh, 1884a: 129-142, pl. IV, figs 25-27, pl. V, figs 1-27, pl. VI, figs 5-18, 20-21; Joyeux-Laffuie 1885: viii-xi.

Paraperonia fidjiensis Labbé, 1934a: 197-198, figs 9-11. Syn. nov.

Peronia verruculata : Mörch 1872a: 28; Mörch 1872b: 325, as vermiculata [non Peronia verruculata (Cuvier, 1830)].

Type material.

Lectotype and paralectotype ( Onchidium peronii ). Mauritius • lectotype, hereby designated, by means of Cuvier’s (1804: pl. 6) anatomical drawings. Timor • 1 paralectotype, 60/40 mm; F Péron leg.; MNHN-IM-2000-22938. The fact that the specimen illustrated by Cuvier cannot be located does not invalidate the lectotype designation ( ICZN 1999: Article 74.4). That individual, according to Cuvier, measured approximately 140 mm long (preserved). Cuvier’s (1804: pl. 6) detailed anatomical drawings are exclusively based on the individual collected by Péron in Mauritius. Note that, although Cuvier’s (1804: pl. 6) illustrations are truly remarkable, they are flipped at 180° because, for instance, the heart and the male anterior parts are on the left. Something must have happened during the engraving or the printing. Hoffmann (1928: 71) referred to Mauritius as the “Typ-Lokalität” of Onchidium peronii but did not formally designate a lectotype for O. peronii . In case of syntypes, "the place of origin of the lectotype becomes the type locality of the nominal species-group taxon, despite any previously published statement of the type locality." ( ICZN 1999: Article 76.2)

The original description of Onchidium peronii was based on two specimens collected by Péron: the lectotype from Mauritius, of which the internal anatomy was illustrated in detail by Cuvier (1804: pl. 6), could not be located and is likely lost; the paralectotype from Timor (MNHN-IM-2000-22938) was very briefly mentioned by Cuvier (1804: 39) who merely wrote that another specimen was brought from Timor by Péron and that Onchidium peronii is present "at the two extreme ends of the Indian Ocean." The paralectotype (60/40 mm) is well preserved even though dorsal papillae with eyes cannot be counted because their color faded. It is obvious that Cuvier did not actually use it for his detailed anatomical description and illustrations on plate 6, because it was never opened prior to the present study, except for a tiny cut near the lung. It was carefully opened on its side to draw a dorsal view of its intestinal loops of type I (Fig. 9A ) and measure the length (4.5 mm) of the spine of the accessory penial gland (by transparency, so that the male copulatory apparatus was not dissected).

Lectotype ( Peronia mauritiana ). Mauritius • lectotype, hereby designated, by means of Cuvier’s (1804: pl. 6) anatomical drawings. The species name Peronia mauritiana was introduced by Blainville (1824: 281) for a species originally illustrated by Cuvier (1804: pl. 6) in the Annales du Muséum d’Histoire naturelle and which Cuvier named Onchidium peronii . Blainville’s reference to Cuvier’s (1804) plate 6 ("La Péronie de l’Isle-de-France [Mauritius]. Peronia mauritiana . Blainv., Cuv., Ann. du Mus., 5, pl. 6.") serves as an indication, and Peronia mauritiana is an available binomen ( ICZN 1999: Article 12.2.1). However, Cuvier’s original description of Onchidium peronii was based on two specimens, a lectotype from Mauritius and a paralectotype from Timor, but Cuvier’s (1804: pl. 6) plate of anatomical drawings exclusively illustrates the lectotype from Mauritius (see above). Because the lectotype of Peronia mauritiana also is the lectotype of Onchidium peronii , Peronia mauritiana remains what it always was, i.e., a junior objective synonym of Onchidium peronii .

Blainville also mentioned the name Peronia mauritiana in his Manuel de Malacologie et de Conchyliologie (Blainville 1825: 490) and in the article “Péronie” of the Dictionnaire des Sciences Naturelles ( Blainville 1826: 523). The illustration published by Blainville (1827: pl. 46, fig. 7) in the Atlas of the Manuel differs from that published by Cuvier (1804: pl. 6, fig. 1). The specimen used by Blainville for that illustration could not be located, which does not matter much since it does not have any name-bearing function. However, it also means that, because there are two species of Peronia in Mauritius, Blainville’s (1827: pl. 46, fig. 7) illustration may or may not refer to Peronia mauritiana .

Lectotype ( Onchidium tonganum ). Tonga • lectotype, hereby designated, 100/60 mm; Panhi-Motou [possibly the small island of Pangaimotu]; MNHN-IM-2000-22937. It is unclear how many specimens Quoy and Gaimard (1832: 210-211, pl. 15, figs 17, 18) examined for the original description of Onchidium tonganum . They may have examined more than one individual. Regardless, it is clear that Onchidium tonganum applies to a Peronia species because the notum of the lectotype bears gills which were also illustrated in the original description. Its notum also bears fifteen dorsal papillae with eyes but others probably faded. The lectotype was dissected prior to the present study. The accessory penial gland and the penial apparatus are missing (pieces of the deferent duct remain). The intestinal loops are of type I with a transitional loop between 2 and 3 o’clock (Fig. 9B ). Quoy and Gaimard (1832: 216) briefly mentioned the presence of O. tonganum in Manokwari, West Papua, Indonesia, but that record could not be confirmed (although P. peronii is known to be present there because Manokwari is the type locality of O. punctatum ).

Lectotype and paralectotypes ( Onchidium punctatum ). Indonesia • lectotype, hereby designated, 70/60 mm; dans le port de Dorey [Manokwari harbor, West Papua]; 1829; JRC Quoy and JP Gaimard leg.; MNHN-IM-2000-22966. • 2 paralectotypes, 35/25 and 32/30 mm; same collection data as for the lectotype; MNHN-IM-2000-33701. An old label of the lectotype says " Onchidium punctatum , Q. G, Ast. pl. 15, fig. 27, de la Nouvelle Guinée, Quoy et Gaimard 1829." That old label does not say “Dorey” (for the locality), which is only mentioned in the original description, but it clearly indicates that the lectotype was part of the type series of Onchidium punctatum . The lectotype bears dorsal gills, as illustrated by Quoy and Gaimard (1832: pl. 15, figs 27, 28). It was dissected prior to the present study, likely by Labbé (1934a: 203-204) and its penis is missing but its intestinal loops are of type I with a transitional loop at 3 o’clock (Fig. 9C ). Its spine of the accessory penial gland, still in place in the animal, is 3.7 mm long.

A second jar was found with two paralectotypes (MNHN-IM-2000-33701). An old label for that second jar says " Onchidium piquetée, Q G. MM Quoy Gaimard, 1829" with no locality data. The name " Peronia " was added on the label. The number “51” also appears on another old label, which corresponds to an unknown numbering system. There also is a more recent label saying " Peronia picta QG, M. Quoy et Gaimard, 1829." Quoy and Gaimard did not describe any onchidiid species with the specific name picta . However, the French vernacular name of Onchidium punctatum in Quoy and Gaimard’s (1832: 215) original description is " Onchidium piquetée.” So, it is likely that these two additional specimens were part of the type series of Onchidium punctatum . Both paralectotypes (35/25 and 32/30 mm) bear dorsal gills. The largest paralectotype was dissected prior to the present study, possibly by Labbé (1934a: 203, 204), and its penis is missing but its accessory penial gland remains. The small paralectotype was not dissected. Labbé (1934a: 203) listed three individuals from Port-Dorey which he (implicitly) regarded as part of the original series of Onchidium punctatum . Labbé gave the measurements for only two individuals: " a " (35/25 mm), likely the largest paralectotype; " b " (77/56 mm), likely the lectotype. In addition, in his re-description of Scaphis punctata , Labbé (1934a: 204-205) mentioned two individuals identified as Peronia and collected by Quoy and Gaimard in 1829, from an unknown locality. Those two individuals are likely within another jar found at the MNHN with the old number “48” and a label saying " Peronia M. Quoy et Gaimard 1829." There is no reason to consider that those two unidentified individuals from the collection of Quoy and Gaimard were part of the type series of Onchidium punctatum . Finally, there is no other old material at the MNHN which could be assigned to the type series of O. punctatum . There are only three other old specimens from Port Dorey at the MNHN: the two syntypes (MNHN-IM-2000-22950) of Wallaconchis ater (Goulding et al. 2018: 63), and one specimen collected by Raffray in 1878 (with numbers “22” and “75” on the label).

Holotype ( Onchidium melanopneumon ). Fiji • holotype, by monotypy, 65/40 mm; Kandavu [Kadavu]; Aug 1874; HMS Challenger leg.; NHMUK 1888.5.30.39. The holotype was entirely dissected by Bergh and is now empty. Given the presence of dorsal gills, Onchidium melanopneumon clearly applies to a Peronia species.

Lectotype and paralectotypes ( Paraperonia fidjiensis ). Fiji • lectotype, hereby designated, 60/50 mm; 1876; Filhol leg.; MNHN-IM-2000-33692. No jar clearly labeled as the type material of Paraperonia fidjiensis was found at the MNHN, but the lectotype could be traced, and six paralectotypes could not be found at the MNHN. Labbé (1934a: 197-198, figs 9-11) described Paraperonia fidjiensis based on seven individuals from Fiji ("Iles Fidji") collected by Filhol (Henri Filhol [1843-1902]) in 1876 and with the following sizes: 75/50 mm for six " a " individuals and 70/50 mm for a seventh " b " individual. Two jars of material collected in Fiji by Filhol in 1876 were found at the MNHN. The first jar, labeled as " Peronia [written over Oncidium ] I. Fidji Mr. Filhol n°11 1876" and “71,” contains a single Peronia specimen which, given its size (60/50 mm), very likely is part of the type series of P. fidjiensis , and which is designated as the lectotype (MNHN-IM-2000-33692). Its radula and all reproductive parts are missing. Its intestinal loops are clearly of type I, with a transitional loop at ~ 1 o’clock (Fig. 9E ). The second jar, labeled as " Oncidiella I. Fidji Mr. Filhol n°11 1876" and “101,” contains four poorly-preserved specimens which do not even appear to belong to Peronia , with a size (less than 30 mm) not compatible with the original description of P. fidjiensis , and which, therefore, cannot be regarded as part of the type series.

Additional material examined.

Mauritius • 2 specimens 140/100 mm [5872] and 125/75 mm [5874]; La Mivoie; 20°20.659'S, 57°21.763'E; 11 Jun 2014; TC Goulding leg.; st 177, basalt rocks, at night; MNHN-IM-2019-1605. • 1 specimen 110/100 mm [3605]; Mahebourg, waterfront; 20°24.317'S, 57°42.605'E; 13 Jun 2014; TC Goulding leg.; st 178, rocky intertidal, with algae, just before sunrise; MNHN-IM-2019-1606. • 1 specimen 100/90 mm [1553]; Grand Port, east side of île Marianne; 20°22.828'S, 57°47.220'E; May 2003; O Griffiths leg.; A2518, out of water on limestone platform; MNHN-IM-2019-1607.

Mariana Islands • 1 specimen 115/80 mm [443]; Guam Island, Bile Bay; 13°17.124'N, 144°39.742'E; 23 Mar 2007; C Carlson leg.; reef margin; CASIZ 180486. • 1 specimen 85/70 mm [5840]; Guam Island, Bile Bay; 13°16.582'N, 144°39.752'E; 27 Nov 2007; C Carlson leg.; shoreline; MNHN-IM-2019-1609.

Papua New Guinea - Madang • 1 specimen 70/60 mm [5476]; Wonad Island; 05°08.1'S, 145°49.3'E; 29 Nov 2012; MNHN Expedition Papua Niugini leg.; st PM43, night tide, sandy beach and intertidal rocks; MNHN-IM-2013-16260. • 1 specimen 65/45 mm [5477]; Wonad Island; 05°08.1'S, 145°49.3'E; 27 Nov & 09 Dec 2012; MNHN Expedition Papua Niugini leg.; st PM41, sandy beach and intertidal rocks; MNHN-IM-2013-15872. • 1 specimen 55/40 mm [5474]; Rempi Area, Barag Island; 05°01.1'S, 145°47.9'E; 15 Nov 2012; MNHN Expedition Papua Niugini leg.; st PM25, fringing reef on narrow barrier island; MNHN-IM-2013-14054. • 1 specimen 80/60 mm [5472]; same collection data as for the preceding; MNHN-IM-2013-14052. • 1 specimen 80/70 mm [5471]; Rempi Area, South Dumduman Island; 05°00.2'S, 145°47.6'E; 9 Nov 2012; MNHN Expedition Papua Niugini leg.; st PM 12, limestone rocky intertidal; MNHN-IM-2013-12500. - New Ireland • 1 specimen 50/40 mm [6086]; Kavieng, Lemus Island; 02°38'S, 150°37.5'E; 12-14 Jun 2014; MNHN Expedition Kavieng 2014 leg.; st KM24, mixed platform with seagrass; MNHN-IM-2013-53482.

Additional material examined

(historical museum collections). Chagos Archipelago • 1 specimen 95/65 mm; Ye Ye, Peros Banhos atoll; 24 Feb 1996; M Spalding (from N Yonow’s personal collection) leg.; exposed on shallow reef flat on rocks; MNHN-IM-2014-7992.

Fiji • 1 specimen 75/50 mm; Viti Isles; A Garrett leg.; ANSP 57967. • 1 specimen 28/25 mm; Viti Levu, Namuka; 18°08'S, 177°23'E; 18 Apr 1917; S Bock’s Pacific Expedition 1917-1918 leg.; barrier reef; SMNH 180357. • 2 specimens 23/20 mm and 15/15 mm; Viti Levu, SW Suva, Namuka; 18°08'S, 177°23'E; 16 Jun 1917; S Bock’s Pacific Expedition 1917-1918 leg.; barrier reef; SMNH 180374. • 1 specimen 37/30 mm; Viti Levu, Namuka; 18°08'S, 177°23'E; 19 Jun 1917; S Bock’s Pacific Expedition 1917-1918 leg.; SMNH 180375. • 1 specimen 80/65 mm; Viti Levu, Bau Island; 17°58'S, 178°36'E; 2 Jul 1917; S Bock’s Pacific Expedition 1917-1918 leg.; reef; SMNH 180373.

India • 2 specimens 85/55 mm and 70/50 mm; Nicobar Islands, Pulo Milo, Little Nicobar; Reinhardt, Galathea 305 leg.; NHMD 613753.

Indonesia - Java • 1 specimen 90/55 mm; Batavia [Jakarta]; 1899; C Aurivillius leg.; SMNH 180355. - Sumatra • 1 specimen 100/70 mm; Sumatra; Deshayes leg.; MNHN-IM-2012-25150. • 1 specimen 65/50 mm; west coast of Sumatra, Pulo Pasu [or Pulu Pasu]; 1891; C Aurivillius leg.; SMNH 180354. - Tanimbar • 1 specimen 60/50 mm; Jamdena Straits, West side of Mitak Island; 07°11'S, 131°28'E; 22 Jun 1970; Mariel King Memorial Expedition Moluccas MV “Pele” 1970 leg.; WAM S26723.

Kiribati • 1 specimen 35/35 mm; Gilbert Islands, Apaiang [Abaiang]; 01°49'N, 172°57'E; 12 Aug 1917; S Bock’s Pacific Expedition 1917-1918 leg.; outer reef; SMNH 180353. • 1 specimen 70/65 mm; Gilbert Islands, Tarawa; 01°26'N, 173E; 16-20 Aug 1917; S Bock’s Pacific Expedition 1917-1918 leg.; reef; SMNH 180382. • 1 specimen 65/50 mm; Gilbert Islands, Aranuka; 00N, 174E; 6 Oct 1917; S Bock’s Pacific Expedition 1917-1918 leg.; reef; SMNH 180376. • 1 specimen 70/50 mm; Gilbert Islands, Aranuka; 00N, 174E; 22 Oct 1917; S Bock’s Pacific Expedition 1917-1918 leg.; outer reef; SMNH 180377. • 1 specimen 30/25 mm; Gilbert Islands, Aranuka; 00N, 174E; 1 Nov 1917; S Bock’s Pacific Expedition 1917-1918 leg.; SMNH 180378. • 1 specimen 15/15 mm; Gilbert Islands, Aranuka; 00N, 174E; 26 Oct 1917; S Bock’s Pacific Expedition 1917-1918 leg.; outer reef; SMNH 180383. • 2 specimens 20/15 mm and 17/13 mm; Gilbert Islands, Aranuka; 00N, 174E; 26 Oct 1917; S Bock’s Pacific Expedition 1917-1918 leg.; outer reef east; SMNH 180384. • 1 specimen 15/12 mm; Gilbert Islands, Aranuka; 00°09'N, 173°35'E; 1917; S Bock’s Pacific Expedition 1917-1918 leg.; outer reef; SMNH 180478. • 1 specimen 65/50 mm; Gilbert Islands; Oct 1917; S Bock’s Pacific Expedition 1917-1918 leg.; outer reef; SMNH 180475. • 1 specimen 80/65 mm; Gilbert Islands, Apamama [Abemama]; 00°24'N, 173°55'E; 1917; S Bock’s Pacific Expedition 1917-1918 leg.; entrance reef; SMNH 180380. • 1 specimen 45/35 mm; Gilbert Islands, Apamama [Abemama]; 00N, 173E; 1917; S Bock’s Pacific Expedition 1917-1918 leg.; at low tide; SMNH 180379.

Madagascar • 1 specimen 65/50 mm; Tulear [Toliara]; 23°22'S, 43°39'E; Feb 1913; K Afzelius leg.; coral reef; SMNH 180381.

Maldive Islands • 1 specimen 85/55 mm; Tiladummati Atoll, Faro Islet, on reef NW of Fildau Island; 06°55.333'S, 73°11.833'E; 30 & 31 Mar 1964; R Robertson, International Indian Ocean Expedition leg.; st R021, intertidal, on dead coral rubble; ANSP 304860.

Marshall Islands • 1 specimen 37/30 mm; Jaluit; 06N, 170E; 20 Oct 1917; C Hessle, S Bock’s Pacific Expedition 1917-1918 leg.; west shore southeast of entrance; SMNH 180356.

Mauritius • 10 specimens up to 90/60 mm; probably Mauritius according to a new label (the original label was destroyed); 1929-1930; T Mortensen leg.; NHMD 613752.

New Caledonia • 1 specimen 100/60 mm; Touho, NW, Koë Reef, 2 mi. SSE; 16-20 Jan 1961; Kline & Orr leg.; 0-4 feet, live and dead coral, sand, weed; ANSP 270221.

Palau • 1 specimen 80/65 mm; ANSP 203028.

Seychelles • 1 specimen 90/70 mm; 1830; Dussumier leg.; MNHN-IM-2012-25149. • 1 specimen 85/60 mm; 1841; L. Rousseau leg.; MNHN-IM-2012-25148.

Tanzania • 1 specimen 65/50 mm; Zanzibar; 1902; C Eliot leg.; ANSP 84336. • 1 specimen 80/65 mm; west coast; Jun 1995; M Richmond & M Toni (from N Yonow’s personal collection) leg.; sheltered, on limestone rock, intertidal exposed at low tide, common at night; MNHN-IM-2014-7991.

GenBank sequence.

One COI sequence was obtained from GenBank (LC390402) for an individual identified as Peronia sp. and collected from Okinawa, Japan ( Takagi et al. 2019), which is the northernmost confirmed locality for Peronia peronii .

Distribution

(Fig. 6 ). Given that our fresh molecular samples of P. peronii from the West Pacific (Guam, Papua New Guinea) are conspecific with those from Mauritius, it is assumed here that all individuals with a long spine of the accessory penial gland belong to the same species. Strictly speaking, however, the presence of P. peronii from places like Zanzibar, the Maldives, Nicobar Islands, West Papua, Timor, Palau, New Caledonia, and Tonga, would still need to be validated with fresh material.

Interestingly, but for unclear reasons, Peronia peronii seems to be only recorded from relatively small islands, the largest ones being Timor, New Caledonia, and Fiji. Even in Papua New Guinea, it was found on small islands close to the mainland but not on the mainland. Peronia peronii seems to be transported across vast distances from the western Pacific Ocean to the western Indian Ocean, but which does not seem to settle on the coasts of large land masses. We did not find it in any of the many localities we visited in the Philippines, Vietnam, Malaysia, Borneo, Sulawesi, Halmahera, Sumatra, etc. It is possible that we occasionally missed it in a few places (obviously we missed it in Timor and New Caledonia where it is present), but it is unlikely that we missed it everywhere.

The presence of P. peronii is confirmed in the following locations (Fig. 6 ): Chagos Archipelago (new record); Fiji (type locality of O. melanopneumon and P. fidjiensis ; Hoffmann, 1928; present study); India, Nicobar Islands ( Mörch 1872a, b: 325, as P. verruculata ; Bergh, 1884a, as O. tonganum ; Hoffmann, 1928; present study); Indonesia, Java ( Hoffmann 1928; present study), Sumatra ( Hoffmann 1928; Labbé 1934a; present study), Tanimbar (new record), Timor ( Cuvier 1804, paralectotype of O. peronii ), West Papua (type locality of O. punctatum Quoy & Gaimard, 1832); Japan, Okinawa ( Takagi et al. 2019, as onchidiids of "Group II"; new record); Kiribati, Gilbert Islands ( Hoffmann 1928; present study); Madagascar ( Odhner 1919; present study); Maldive Islands ( Marcus and Marcus 1960, 1970; present study); Mariana Islands, Guam ( Dayrat et al. 2011; White et al. 2011; present study); Marshall Islands ( Hoffmann 1928; present study); Mauritius (type locality of O. peronii and P. mauritiana ; Semper 1880; Bergh 1884a, as O. tonganum ; Plate 1893; present study); New Caledonia (new record); Palau (new record); Papua New Guinea, Madang (new record), New Ireland (new record); Seychelles ( Labbé 1934a; present study); Tanzania, Zanzibar (new record); and Tonga (type locality of O. tonganum Quoy & Gaimard, 1832). The most western records of P. peronii are Zanzibar and southwestern Madagascar; its most eastern records are Okinawa, Guam, Kiribati, and Tonga. Note that P. peronii is most likely also present in Tokara Islands ( Baba 1958: 144, as O. verruculatum ), just south Kyushu, ca. 30N, which would be its most northern record.

The following records from the literature are not confirmed here, because authors did not provide enough information supporting the identification: Djibouti ( Vayssière 1912; O’Donoghue 1929; Labbé 1934a); India, Nicobar ( Godwin-Austen 1895, as O. mauritianum ; Patil & Kulkarni, 2013); Indonesia, West Papua (Quoy and Gaimard 1832, as O. tonganum ); Japan ( Arimoto et al. 1993); Kenya ( Martens 1897); Madagascar ( Marcus and Marcus 1970); Mariana Islands, Guam ( Biskupiak and Ireland 1985); Mozambique ( Martens 1879; Connolly 1912, 1939; Macnae and Kalk 1958); Papua New Guinea, New Ireland ( Labbé 1934a, as P. tongana ); Persian Gulf ( White 1951; Bitaab et al. 2015); Philippines ( Casto de Elera 1896, as O. tonganum ), Bohol (Semper 1880, as O. tonganum ); Red Sea ( Sturany 1904); Samoa (Semper 1880, as O. tonganum ); South Africa, Natal ( Krauss 1848; Sturany 1898; Collinge 1910; Connolly 1912, 1939; Morrisey et al. 2010); Australia, Lord Howe Island ( Bretnall 1919; Hoffmann 1928), Torres Strait ( Smith 1884, as Onchidium punctatum ), Western Australia ( Bretnall 1919).

Etymology.

Onchidium peronii was named after François Péron [1775-1810] who collected the two slugs described by Cuvier during the Baudin expedition [1800-1803]. Peronia mauritiana , Onchidium tonganum , and Paraperonia fidjiensis were named after type localities. Onchidium punctatum was named after the speckled ( punctatum in Latin) dorsal notum of live animals. Onchidium melanopneumon was named after the black (melas in Greek) lung (pneumon in Greek) tissue of the holotype.

Habitat

(Fig. 7 ). Live slugs of Peronia peronii are found in the rocky intertidal, like most other Peronia slugs. Many of our specimens were collected at night or just before sunrise, suggesting that P. peronii is, at least partly, a nocturnal species. This could explain why we missed it at some localities where we only collected during the day. Peronia peronii is not rare, but it is definitely not as common as some other species. The fact that collecting it at night seems necessary, at least in some localities, might explain why collections of P. peronii are not as abundant as collections of P. verruculata .

Color and morphology of live animals

(Fig. 8 ). No picture of live animals was available for individuals from the West Pacific (Guam and Papua New Guinea). The description of the color of live animals is based on the Mauritius individuals. The dorsal notum is brown, with a greenish hue, light to dark, mottled with darker and lighter areas. The color of the dorsal papillae varies a s that of the background itself. The ventral surface (foot and hyponotum) is yellowish-greenish and can change rapidly in any given individual. The ocular tentacles are brown-grey, like the head. The dorsal notum of live animals is covered by dozens of papillae of various sizes. Dorsal papillae can be particularly tall (easily up to 4 mm), even in preserved specimens, and are evenly distributed over the entire notum. Preserved, they are difficult to distinguish from retracted dorsal gills in the posterior half of the notum. Some papillae bear black dorsal eyes at their tip. The number of papillae with dorsal eyes is variable (15-20). The longest animals are 140 mm long in Mauritius and 115 mm long in the West Pacific.

Digestive system

(Figs 9 - 12 ). Examples of radular formulae are presented in Table 5 . The median cusp of the rachidian teeth is approximately 75 μm long. The hook of the lateral teeth is approximately 160-200 μm long. The intestinal loops are of type I, with a transitional loop oriented between 12 to 3 o’clock.

Reproductive system

(Figs 13 - 16 ). In the anterior (male) parts, the muscular sac of the accessory penial gland is at least 30 mm long in specimens from Mauritius and at least 25 mm long in specimens from the West Pacific (Guam & Papua New Guinea). Note that, in some additional museum specimens, the muscular sac was only 20 mm long, and, even exceptionally 17 mm long (see remarks below). The hollow spine of the accessory penial gland is narrow, elongated, and straight or slightly curved, and its shape (including at its tip) varies between individuals. Its length ranges from 3.4 mm ([5872] MNHN-IM-2019-1605) to 3.6 mm ([3605] MNHN-IM-2019-1606) in Mauritius, and from 3.5 mm ([5472] MNHN-IM-2013-14052) to 4 mm ([5471] MNHN-IM-2013-12500) in the West Pacific (Guam and Papua New Guinea). Its diameter at the conical base is approximately 400 μm in specimens from Mauritius and between 400 and 500 μm in specimens from the West Pacific (Guam and Papua New Guinea). Its diameter at the tip measures 160-170 μm in specimens from the West Pacific, and from 180 to 200 μm in specimens from Mauritius. Note that, in some additional museum specimens, the spine was only 3 mm long (see remarks below).

The retractor muscle is shorter or longer than the penial sheath and inserts near the heart. Exceptionally, the retractor muscle can even be vestigial ([5472] MNHN-IM-2013-14052). Inside the penial sheath, the penis is a narrow, elongated, soft, hollow tube. Its distal end bears conical hooks which are less than 50 μm long.

Diagnostic features

(Table 4 ). Peronia peronii is the only Peronia species which is easy to identify anatomically. Indeed, it is characterized by a very long spine (at least 3 mm) of the accessory penial gland, which is distinctive and easily accessible (one just needs to pull on the flagellum of the penial gland or, even, in some cases, measure the spine by transparency). The two longest spines were found in the lectotype of P. fidjiensis (MNHN-IM-2000-33692) from Fiji (5 mm), and in an old historical specimen (ANSP 304860) from the Maldives (4.8 mm).

Peronia peronii is additionally characterized by a unique combination of anatomical traits: muscular sac longer than 20 mm, intestinal loops of type I (with a transitional loop oriented between 12 and 3 o’clock), retractor muscle inserting near the heart. Also, no individual larger than 80 mm was found in any other Peronia species so far. Animal size can be useful when several Peronia species are found at the same site. For instance, the two individuals of P. verruculata (unit #1) found at the station PM 12 (near Madang, Papua New Guinea) are 35 and 38 mm long while the individual of P. peronii from the same station is 80 mm long. The type I of its intestinal loops (with a transitional loop oriented between 12 and 3 o’clock) is only shared by P. okinawensis , a species endemic to Japan with which it is most closely related.

Remarks.

Synonymies. There is no doubt that Cuvier’s (1804) Onchidium peronii applies to the species described here, just based on animal size alone. According to Cuvier, the lectotype from Mauritius measured approximately 140 mm long and our molecular data show that all individuals of that size from Mauritius belong to a single species (Table 4 ). Cuvier’s (1804: pl. 6) detailed anatomical description and drawings are exclusively based on the lectotype (he did not dissect the paralectotype from Timor). Cuvier (1804: 48, pl. 6, fig. 8) described the spine of the accessory penial gland as a "very sharp, brown spike" but unfortunately did not provide its length. However, Cuvier’s (1804: pl. 6, fig. 4) illustration of the intestinal loops is identical to some of our Mauritius individuals here: intestinal loops of type I with a transitional loop at 3 o’clock. The paralectotype of Onchidium peronii from Timor (MNHN-IM-2000- 22938) is only briefly mentioned by Cuvier in the original description. The length (4.5 mm) of the spine of its accessory penial gland (checked for the present study) indicates that it also belongs to P. peronii . Its intestinal loops are also identical to those of the lectotype (Fig. 9A ).

Peronia mauritiana is a junior objective synonym of Onchidium peronii because they share the same name-bearing type.

Onchidium tonganum was described by Quoy and Gaimard (1832: 210-211, pl. 15, figs 17, 18) from “Panhi-Motou,” possibly the small island of Pangaimotu, Tonga, based on an unspecified number of individuals. The illustrations of the dorsal gills by Quoy and Gaimard (1832: pl. 15, figs 17, 18) and their presence on the notum of the lectotype (MNHN-IM-2000-22937) clearly indicate that Onchidium tonganum belongs to Peronia . The lectotype was dissected prior to the present study and most of the male copulatory parts are missing (only the deferent duct remains). As a result, the length of the spine of the accessory penial gland, which is diagnostic of P. peronii , cannot be checked. Labbé (1934a: 191) listed the lectotype in the material he examined for his re-description of P. tongana , but he did not point out that it was part of the type material of O. tonganum and he did not describe it anatomically. It is possible but not certain that Labbé dissected the lectotype. At any rate, its intestinal loops are of type I with a transitional loop between 2 and 3 o’clock (Fig. 9B ). Both the length (100 mm) of the lectotype as well as its intestinal loops indicate that Peronia tongana is a junior synonym of P. peronii (Table 4 ).

Onchidium punctatum is regarded here as a junior synonym of P. peronii because the length (3.7 mm) of the spine of the accessory penial gland of the lectotype (MNHN-IM-2000-22966) is only compatible with P. peronii (Table 4 ). The length of the lectotype (70 mm, preserved) is also far more compatible with P. peronii than with P. verruculata , another species found in West Papua. Our many individuals of P. verruculata are all less than 60 mm long (alive), except a single individual from New Caledonia (73 mm alive). Given their small size, the two paralectotypes (MNHN-IM-2000-33701) likely belong to P. verruculata (unit #1) instead of P. peronii , which would not be surprising at all because the type locality of O. ferrugineum (a junior synonym of P. verruculata ) is the same as that of O. punctatum (Manokwari, West Papua, Indonesia). At the end of the description of O. punctatum , Quoy & Gaimard (1832: 216) also mention in passing that they also found Onchidium tonganum in Port Dorey (i.e., Manokwari, West Papua, Indonesia) and they even point out that local inhabitants know how to distinguish both species. Both O. punctatum and O. tonganum are regarded here as junior synonyms of P. peronii . However, it remains true that there are two sympatric Peronia species in West Papua, P. verruculata and P. peronii , which can be distinguished in the field based on animal length (except, of course, for individuals measuring less than 60 mm long).

Bergh (1884a: 129-142, pl. IV, figs 25-27, pl. V, figs 1-27, pl. VI, figs 5-18, 20, 21) described Onchidium melanopneumon from a single individual (65/40 mm) from Fiji. This specimen was completely dissected by Bergh and is now empty (NHMUK 1888.5.30.39). Onchidium melanopneumon applies to a Peronia species due to the presence of dorsal gills, and the length (4 mm) of the spine of the accessory penial gland indicates that it applies to P. peronii (Table 4 ). Its intestinal loops ( Bergh 1884a: pl. V, fig. 27) are also similar to those found in P. peronii , although the transitional loop is slightly past the 3 o’clock limit. As a result, O. melanopneumon is regarded as a junior synonym of P. peronii . Bergh (1884b: 263; 1885: 176) briefly mentioned again O. melanopneumon in a comparative study on the affinities of onchidiids.

Labbé (1934a: 197-198, figs 9-11) described Paraperonia fidjiensis based on seven individuals from Fiji, one of which could be found and is designated as the lectotype (MNHN-IM-2000-33692). Because all reproductive parts are missing, the length of the spine of the accessory penial gland cannot be checked. However, according to Labbé (1934a: 197, fig. 10), the spine of the accessory penial gland is 5 mm long, which is only compatible with P. peronii (Table 4 ), and is the longest spine known in P. peronii . The intestinal loops of the lectotype of P. fidjiensis are clearly of type I, with a transitional loop oriented at ~ 1 o’clock (Fig. 9E ), even though Labbé (1934a: 197) erroneously described them a type V, which is a mistake he often made. Given the length of the lectotype (60 mm) and, most importantly, the length of the spine of the accessory penial gland, P. fidjiensis is regarded as a junior synonym of P. peronii .

Secondary literature. Several early authors mentioned Cuvier’s Onchidium peronii without any new material ( Cuvier 1816: 411; Cuvier 1830: 46; Férussac 1822: xxxi; Fleming 1822a: 574; Fleming 1822b: 463; Lamarck 1822: 46; Voigt 1834: 101). Oken (1834a: 287) transferred Quoy and Gaimard’s (1832) Onchidium tonganum and O. punctatum to Peronia but with no justification.

In the seventh volume of the second edition of Lamarck’s Histoire naturelle des animaux sans vertèbres, which was revised by Deshayes and Milne-Edwards (1836), P. mauritiana is proposed as a synonym of Onchidium peronii . However, as a reference for P. mauritiana , the authors mentioned the illustration published by Blainville (1827: pl. 46, fig. 7) in the Atlas of his Manuel which differs from that published by Cuvier (1804: pl. 6, fig. 1) and may or may not refer to Peronia mauritiana .

John Edward Gray (1850: 117) listed Onchidium peronii as a synonym of P. mauritiana and his wife Maria Emma Gray (1850: pl. 181, fig. 7) reproduced Cuvier’s (1804: pl. 6, fig. 1) original figure of the dorsal notum of Onchidium peronii . As a result, JE Gray (1850: 117) and ME Gray (1850: pl. 181, fig. 7) are listed above as correct references of O. peronii . In the same work, JE Gray (1850: 117) regarded P. punctata and P. tongana (as spelling mistake tongensis ) as valid, and ME Gray (1850: pl. 182, fig. 1, pl. 183, fig. 3) reproduced the original illustrations by Quoy and Gaimard (1832: pl. 15, figs 17, 18, 27, 28). As a result, those names are also listed above as correct references. According to JE Gray (1850: 117), P. mauritiana (as mauriciana) was a valid Peronia species name but ME Gray (1850: pl. 183, fig. 2) reproduced Blainville’s (1827: pl. 46, fig. 7) illustration which differs from that published by Cuvier (1804: pl. 6, fig. 1) and which may or may not refer to P. peronii because there are two Peronia species in Mauritius (Fig. 6 ). Therefore, ME Gray’s (1850: pl. 183, fig. 2) Peronia mauritiana is not listed above as a correct reference of P. peronii . And, finally, ME Gray’s (1850: pl. 183, figs 4, 4a, 5) reproductions of Savigny’s (1817: pl. II, figs 3.1-3.3) illustrations of Onchidium peronii from the Red Sea do not represent P. peronii (see remarks on P. verruculata ).

Adams and Adams (1855: 235) merely listed Peronia mauritiana , P. peronii , P. punctata , and P. tongana as Peronia species names. Note that for P. peronii , they refer to Savigny’s illustrations of individuals from the Red Sea misidentified as P. peronii by Audouin instead of Cuvier’s original description of P. peronii , which means that Adams and Adams refer to P. verruculata instead of P. peronii (see remarks on P. verruculata ). Adams and Adams (1855: pl. LXXXI, fig. 3) also reproduced the original illustration of O. tonganum by Quoy and Gaimard (1832: pl. 15, fig. 17).

Berge (1855: 124) mentioned " Onchidium peronii Cuv." from the East Indies and the Red Sea but with no new material or literature reference except for a German translation of Cuvier’s Règne Animal by Voigt (1834: 101) as well as "Cuvier, Règ. anim. pl. 26, fig. 2." Berge (1855: 124) followed Voigt (1834: 101) and accepted P. mauritiana as a synonym of O. peronii . Cuvier’s illustration (pl. 26, fig. 2) mentioned by Berge was actually published after Cuvier’s death in the Disciples’ edition of the Règne Animal which was accompanied by beautiful illustrations. According to Cowan (1976), the authorship for the mollusks should be attributed to Deshayes (1836-1845) who prepared the volume of text and the atlas published in livraisons between 1836 and 1845. However, the exact dates of publication are still unknown for most pages and plates, including for the page 69 and the plate 26 where Onchidium is mentioned and illustrated. Note the spelling mistake Unchidium on the figure caption of plate 26. The illustrations in both Deshayes (1836-1845: pl. 26, fig. 2) and Berge (1855: pl. 16, fig. 8) are mere reproductions of Cuvier’s (1804: pl. 6, fig. 5) anatomical drawing of O. peronii . Berge (1855: 124) also mentioned " Onchidium punctatum Quoy" from Australia (as Neuholland) but with no new material or literature reference except for another illustration (pl. 26, fig.1) from the Disciples’ edition of the Règne Animal. Again, the illustrations in both Deshayes (1836-1845: pl. 26, fig. 1) and Berge (1855: pl. 21, fig. 7) are mere reproductions of Quoy and Gaimard’s (1832: pl. 15, fig. 27) original illustration of O. punctatum . It cannot be determined which species Berge referred to exactly (because the localities mentioned by Berge are not the type localities).

The record of Onchidium peronii from Natal, South Africa ( Krauss 1848: 72) likely is a record of P. madagascariensis , the only Peronia species known in South Africa so far (see remarks on P. madagascariensis ). However, P. verruculata (unit #5) could also be present in northeastern South Africa because its southernmost known locality is in Maputo, Mozambique (ca. 26°S). This record by Krauss was mentioned again by a few authors ( Sturany 1898: 73; Collinge 1910: 171; Connolly 1912: 224-225; Connolly 1939: 454).

Chenu (1859: 474, fig. 3505) mentioned Peronia punctata with no additional material or records, and with a reference to Quoy and Gaimard’s (1832: pl. 15, fig. 27) original illustration of O. punctatum .

Keferstein (1865a: pl. CII, fig. 20) reproduced Quoy and Gaimard’s (1832: pl. 15, fig. 17) original illustration of Onchidium tonganum , which he classified in Peronia . Keferstein (1865a: pl. CIII, fig. 1) also reproduced Cuvier’s (1804: pl. 6, fig. 4) original illustration of the internal anatomy of O. peronii , which he also classified in Peronia .

Based on the collections of the Galathea Expedition preserved in Copenhagen, Mörch (1872a: 28; 1872b: 325) mentioned Peronia verruculata (as spelling mistake vermiculata in 1872b) from Pulo Milu [Pulo Milo, Little Nicobar] and Nancouri [Nancowry, Nicobar Islands], where he says it is common. Given the animal size (up to 133 mm long alive), we agree with Hoffmann (1928: 71) that Mörch’s record is very likely a record of P. peronii . The preserved specimen (88/38 mm) reported by Mörch (1872a: 28; 1872b: 325) from the Galathea collections most likely is the specimen identified by Semper as Onchidium tonganum , described by Bergh (1884a: 142-148, pl. VI, fig. 19, pl. VII, figs 1-6), examined by Hoffmann (1928: 44) for his description of O. peronii , and finally re-examined for the present study (NHMD 613753). Bergh (1884b: 264; 1885: 177) briefly mentioned O. tonganum again in a comparative study on the affinities of onchidiids. Mörch (1872a: 28; 1872b: 325) mentioned Peronia mauritiana from Sambelong, Great Nicobar, Nicobar Islands, based on much smaller individuals from the collections of the Galathea Expedition in Copenhagen, which are a record for Peronia verruculata (see remarks on that species).

The record of Onchidium mauritianum from the Red Sea by Pagenstecher (1877: 62) refers to either Peronia verruculata or P. madagascariensis (Fig. 6 ).

The records of Onchidium peronii from Mozambique by Martens (1879: 735) in Ibo Island (ca. 12°21'S) and Inhambane (ca. 23°52'S) are within the geographical range of both P. verruculata (unit #5) and P. madagascariensis (Fig. 6 ). It is not possible to know to what species Martens was referring; this record by Martens was mentioned twice by Connolly (1912: 225; 1939: 454).

Semper (1880: 258-260, pl. XIX, figs 2, 9, pl. XXII, figs 1, 2, 10) referred to huge onchidiid slugs (from 50 to 105 mm, preserved) as Quoy and Gaimard’s (1832) Onchidium tonganum and merely suggested, with a question mark, that O. peronii could refer to the same species. Semper (1880: 258) listed five geographical records for O. tonganum : Tonga and West Papua (as Port Dorey), from Quoy and Gaimard (1832); Mauritius, based on some material from the Vienna and Kiel museums; Samoa, based on some material from the Museum Godeffroy; and Bohol, Philippines, based on his own collections. Semper (1880: 258) indicated that the specimens he examined were from 50 to 105 mm long, preserved, and that the smallest individual was found in Mauritius. His anatomical description perfectly matches the anatomy of P. peronii . In particular, a spine of an accessory penial gland measuring 4 mm long is only compatible with P. peronii (Table 4 ). However, he did not clearly indicate whether he observed a long spine in every specimen. It cannot be excluded that he measured the length of the accessory penial gland spine only in a specimen from Mauritius. Therefore, the records of P. peronii in Bohol and in Samoa are regarded here as questionable, even though it is very possible that P. peronii lives in Samoa, given that it is so close to Tonga (800 km) and Fiji (1100 km).

Semper (1882: 290) thought that Cuvier’s (1804) original description of P. peronii was problematic because his drawing of the dorsal notum did not match the internal anatomy. Because Semper was convinced that Cuvier used specimens that did not belong to the same species, he thought that the name P. peronii should not be used. Plate (1893: 172-173) disagreed with Semper even without examining the type material of P. peronii . It is demonstrated here that the two type specimens described by Cuvier as P. peronii both belong to the same species (see above). Semper (1882: 268) was undecided about the nomenclatural status of what he called Onchidium mauritianum (then a new combination), which he listed as one of the names for which a "closer inspection of the originals" was needed. Like most authors, he cited Blainville’s (1827: pl. 46, fig. 7) illustration (which is not part of Blainville’s original description) as a reference without realizing that it may or may not correspond to P. mauritiana , a junior objective synonym of P. peronii . Semper (1882: 289) was also undecided about the status of Onchidium punctatum , for which he erroneously thought that the type locality was unknown. He suggested that it might refer to the same species as Onchidium tumidum , which is not possible because O. tumidum was recently transferred to Paromoionchis ( Dayrat et al. 2019a).

Tapparone Canefri (1883: 214) listed all of Semper’s geographic records for Peronia tongana with no new material or anatomical observations (see above). Tapparone Canefri (1883: 214) also regarded Peronia punctata as a valid species name, but with no other reference or material than the original description by Quoy and Gaimard (1832). Tapparone Canefri’s suggestion that Peronia punctata could refer to the same species as Onchidium tumidum must be rejected because O. tumidum was recently transferred to Paromoionchis ( Dayrat et al. 2019a).

Smith (1884: 92) mentioned Onchidium (Peronia) punctatum from Albany Island and Thursday Island, in the Torres Strait, without any description. This is likely a record of Peronia verruculata (unit #1), the only species thought to be present in the Torres Strait, although our study does not include any fresh material from the Torres Strait and P. peronii could also live there (Fig. 6 ). Note that Thursday Island also happens to be the type locality of Scaphis viridis , a junior synonym of Peronia verruculata .

Bergh (1884a: 142-148, pl. VI, fig. 19, pl. VII, figs 1-6) described as Onchidium tonganum a specimen from the collections of the Copenhagen Museum which was collected in the Nicobar Islands during the Galathea Expedition (station 305). That specimen (85/55 mm), dissected by Bergh, is in a jar (NHMD 613753) with a second specimen (70/50 mm) which is still entire and not dissected by Bergh. Both specimens were re-examined for the present study, although Bergh’s measurement of the penial gland spine in the largest specimen (4.25 mm) could not be checked because internal organs are missing. Given the specimen sizes, their intestinal loops (type I with a transitional loop at 3 o’clock in the second specimen), and the spine of their accessory penial glands (4.25 mm in the largest specimen according to Bergh, and 4 mm in the second specimen), those two specimens belong to P. peronii .

Joyeux-Laffuie (1885: viii-xi) merely mentioned O. melanopneumon in a summary of Bergh’s (1884a) work.

Plate (1893: 172-173, pl. 12, figs 85, 87, 91) re-described Onchidium peronii based on at least one specimen from Mauritius for which he did not provide any size. However, given the length of the spine of the accessory penial gland (7 mm long), there is no doubt that he examined P. peronii . It is possible that he included a part of the duct of the accessory penial gland in that measurement because the longest spine observed in the present study was 5 mm, in the lectotype of P. fidjiensis (MNHN-IM-2000-33692). According to Plate, the retractor muscle inserts near the central nervous system, which does fit in the variation observed here (Table 4 ). Plate listed several synonyms: Peronia mauritiana , Onchidium tonganum , O. melanopneumon , and possibly (with a question mark) P. corpulenta . Note that Plate (1893: 172) rightly regarded O. melanopneumon as a junior synonym of O. peronii but for a weak reason (a similar pigmentation of the lung). These synonymies are all accepted here, except for P. corpulenta which is regarded as a nomen dubium (see general discussion). Plate (1893) did not comment on O. punctatum .

Godwin-Austen (1895: 443) listed Onchidium mauritianum in Little Nicobar. It is impossible to know what species was referred to. However, P. peronii (of which P mauritiana is a junior synonym), is known to be present in Nicobar Islands.

Casto de Elera (1896: 629) mentioned the presence of several species in the Philippines, without description or new material, mostly based on Semper’s (1880-1885) work: Onchidium verruculatum , O. tonganum , and O. savignyi (as savigngi). Our data suggest that Peronia verruculata (unit #1) lives in the Philippines (Fig. 6 ).

Martens (1897: 126) listed Peronia mauritiana as a synonym of Onchidium peronii with a reference to Blainville’s (1827: pl. 46, fig. 7) illustration of P. mauritiana which may or may not refer to P. mauritiana . Martens (1897: 126) also claimed that O. tonganum is a synonym of O. peronii , with a reference to the original description by Quoy and Gaimard (1832) as well as to Semper’s (1880: 258-260, pl. XIX, figs 2, 9, pl. XXII, figs 1, 2, 10) re-description, which may only partly correspond to P. peronii (see above). The record of O. peronii in Mombasa (Mombas, Ostküste Afrika) by Martens (1897: 126) is not supported by any description and is therefore not accepted here, even though it is possibly correct ( P. peronii is present in Zanzibar).

Collinge (1900: 7) and Connolly (1912: 225) mentioned Onchidium peronii from Green Point, Cape Peninsula, South Africa. Those specimens were later used by Watson (1925: 283-284, pl. XXVII, figs 4-11, pl. XXVIII, figs 12, 14, pl. XXXI, fig. 58) to describe Onchidella capensis Watson, 1925.

Sturany (1904: 269) mentioned the presence of Onchidium peronii in Massawa, Eritrea, Red Sea. This record most likely refers to either Peronia verruculata or P. madagascariensis (Fig. 6 ).

Onchidium punctatum is one of the eight onchidiid species mentioned by Hedley (1909: 369) from Queensland, Australia, without any reference to any material. It is impossible to know what species Hedley refers to. Our data show that there are two Peronia species in Queensland (Fig. 6 ).

The record of Onchidium peronii from Durban, Natal, South Africa by Collinge (1910: 171) likely is a record of P. madagascariensis , the only Peronia species known in South Africa so far (see remarks on P. madagascariensis ). However, P. verruculata (unit #5) could also be present in northeastern South Africa because its southernmost known locality is in Maputo, Mozambique (ca. 26°S). This record was mentioned again by Connolly (1912: 225; 1939: 454).

According to Connolly (1912: 224-225), Onchidium peronii is a valid name and Peronia mauritiana (as spelling mistake mauritziana) and O. tonganum are its synonyms. The references listed by Connolly are all commented on above. Let us briefly emphasize here, however, that the localities of Onchidium peronii mentioned by Connolly in South Africa and Mozambique are problematic. Connolly (1939: 454) later admitted that "it is open to question (...) whether the true O. peronii Cuv. really exists in South Africa." Connolly (1939:453), who did not cite Labbé’s (1934a) work, considered that Peronia was a subgenus of Onchidium and should include onchidiid slugs with dorsal gills.

Vayssière (1912: 125-129) recorded seven individuals of Peronia peronii shipped to him from Moucha Islands (Djibouti) by Charles Gravier and Félix Pierre Jousseaume, two of the people who also collected many specimens studied by Labbé (1934a). Vayssière mostly focused on the description of the radula, which is not useful to identify species. Vayssière reported a wide range of animal sizes (from 10 to 80 mm long and from 6 to 60 mm wide). Thus, it is very possible that he examined more than one species. Instead of P. peronii , which has never been positively recorded from Djibouti, Vayssière likely examined P. verruculata , P. madagascariensis , or both (Fig. 6 ). His specimens of large size most likely were P. madagascariensis because P. verruculata individuals rarely are longer than 60 mm (Table 4 ). Note that the number of rows of teeth and the number of teeth per half row mentioned by Vayssière (95 to 100 rows on average) are higher than what was observed here, although they are more compatible with P. madagascariensis than P. verruculata (Table 5 ), acknowledging that radular formulae are expected to vary.

It is not possible to determine to what species Odhner (1919: 42) was referring solely based on his brief, external description of Onchidium peronii from Toliara, Madagascar. However, his material, dissected here, clearly belongs to P. peronii : a single individual (65/50 mm) is characterized by intestinal loops of type I with a transitional loop at 3 o’clock, a spine of the accessory penial gland of 3 mm long, and a muscular sac of 25 mm long (SMNH 180381).

Bretnall (1919) uncritically took for granted every species record ever published, without considering that species often are misidentified. Bretnall (1919) accepted O. peronii as a valid name, with Onchidium tonganum and Peronia mauritiana as synonyms, and P. corpulenta as a potential synonym (with a question mark). The references listed by Bretnall (1919: 311-312) for O. peronii are all commented on above already. However, Bretnall’s (1919: 313) list of geographic records needs to be discussed, especially because Bretnall did not mention the key characters supporting a proper identification of P. peronii (Table 4 ). The presence of P. peronii in Samoa, which Bretnall obtained from Semper (see above), should not be taken for granted, even if it is quite possible. The presence of P. peronii in the Buccaneer Archipelago, northern Western Australia (16S, 123E), based on specimens from the Australian Museum, should not be taken for granted, even though it is quite possible. The identification of P. peronii in the Santa Cruz Islands, Solomon Islands, based on specimens from the Australian Museum, should not be taken for granted (specimens may have been misidentified), even if the Santa Cruz Islands are within the known geographical range of P. peronii (Fig. 6 ). Bretnall (1919: 315-316) also regarded O. melanopneumon as a valid name, for which he cited Bergh’s (1884a) original description and its French summary by Joyeux-Laffuie’s (1885), and indicated Plate’s (1893) proposed synonymy (with O. peronii ) with a question mark. Bretnall (1919: 316) listed Lord Howe Island, off southeastern Australia (based on specimens from the Australian Museum), as a locality for O. melanopneumon , but without description of key characters. Thus, the presence of P. peronii in Lord Howe Island, which is 1350 km south of the southernmost known locality of P. peronii (New Caledonia), is not taken for granted here. As for Onchidium punctatum , Bretnall (1919: 316-317) followed Semper (1882: 289) and Tapparone Canefri (1883: 214) who both thought that it could be a synonym of Onchidium tumidum (see above), which is not possible because O. tumidum refers to a Paromoionchis species ( Dayrat et al. 2019a).

Hoffmann (1928: 71), following most of Plate’s (1893) nomenclatural decisions, accepted Peronia mauritiana , P. corpulenta , Onchidium tonganum and O. melanopneumon as junior synonyms of O. peronii . Hoffmann, like other authors, did not mention the key anatomical characters that allow a reliable identification of P. peronii and uncritically accepted most geographical records published before him. As a result, his proposed distribution for O. peronii should not be taken for granted. For instance, the presence of P. peronii in Lord Howe Island, off southeastern Australia, obtained from Bretnall (1919) is questionable. Hoffmann (1928: 44) examined a specimen from the Nicobar Islands (NHMD 613753) which was originally mentioned by Mörch (1872a: 28; 1872b: 325; see above). Hoffmann (1928: 44-45) also provided several geographical records (Sumatra, Java, Marshall Islands, Kiribati, Fiji) for O. peronii based on material preserved at the SMNH in Stockholm. His material was re-examined and all records are confirmed. Hoffmann only dissected two individuals, one from Sumatra (SMNH 180354) and one from Kiribati (SMNH 180379). The other eighteen specimens were dissected for the present study.

Eight large specimens (longer than 65 mm) examined by Hoffmann from Sumatra (SMNH 180354), Java (SMNH 180355), Kiribati (SMNH 180376, 180377, 180380, 180382, 180475), and Fiji (SMNH 180373) share the diagnostic characteristics of P. peronii : a spine of the accessory penial gland between 3 and 4 mm long, intestinal loops of type I with a transitional loop at 3 o’clock, and a muscular sac between 20 and 25 mm long (exceptionally 17 mm, SMNH 180354). Seven smaller specimens (between 15 and 37 mm long) examined by Hoffmann from the Marshall Islands (SMNH 180356), Fiji (SMNH 180374), and Kiribati (SMNH 180353, 180383, 180384) are immature: the anterior male reproductive parts are barely developed, and, if present, the spine of the accessory penial gland is still soft (SMNH 180353). Given their intestinal loops (type I with a transitional loop at 3 o’clock), they are regarded as individuals of P. peronii . In other species, individuals of that size are already fully mature. Two smaller specimens (between 28 and 37 mm long) examined by Hoffmann from Fiji (SMNH 180357, 180375) belong to P. peronii because of several characteristics (retractor muscle inserting near the heart, intestinal loops of type I with a transitional loop at 3 o’clock, a spine of 3 mm long). Their muscular sacs (11 and 15 mm) are shorter than in other specimens, suggesting that they likely are not fully mature. Two specimens from Kiribati (SMNH 180378, 180478), poorly preserved, could not be confidently identified. Finally, the male reproductive parts are missing in a specimen from Kiribati dissected by Hoffmann (SMNH 180379), but its intestinal loops (type I with a transitional loop oriented between 1 and 2 o’clock) confirm that it belongs to P. peronii .

Note that the locality of the specimen from Sumatra (SMNH 180354) is problematic. The label and Hoffmann’s publication both say "Pulu Pasu, west coast of Sumatra," but there is no such place on the west coast of Sumatra. There are two small islands off the west coast of Sumatra called Pulau Asu (Hinako Islands) and Pulau Pasumpahan (south of Padang). There also is a small island called Pulau Pasu in the Riau Islands, but that archipelago is located north of Sumatra, in the South China Sea. So, it is unclear where that specimen was collected exactly in Sumatra.

O’Donoghue (1929: 833) reported one specimen (30/21 mm) of Peronia peronii from Port Taufiq, Suez, Egypt. A radular formula (65 × 72-1-72) is not enough to identify a Peronia species, and he most likely examined P. verruculata or P. madagascariensis (Fig. 6 ).

Two names accepted as valid by Labbé (1934a) are regarded as synonyms of Peronia peronii : P. tongana , and P. fidjiensis . Labbé (1934a: 191) himself acknowledged that differences between P. peronii and P. tongana were weak. The traits that he mentioned (position of the pneumostome with respect to the anus, head longer than the foot) vary greatly due to preservation. Labbé (1934a: 197-198) did not compare Paraperonia fidjiensis with Peronia peronii probably because he classified them in two distinct genera. However, there are no differences between the type material of P. fidjiensis and the type material of P. peronii . Labbé (1934a: 190) agreed with most authors that P. mauritiana and O. melanopneumon were synonyms of P. peronii . Like Plate (1893), Labbé (1934a: 190) thought that P. corpulenta was simply a potential synonym of P. peronii but in fact it is a nomen dubium (see general discussion).

All references cited by Labbé for P. peronii and P. tongana have been commented on above, but Labbé’s (1934a) proposed distribution ranges need additional clarification. Labbé’s (1934a: 190-191) re-description of P. peronii was based on one individual (100/70 mm) from Sumatra (MNHN-IM-2012-25150), one individual (90/70 mm) from the Seychelles (MNHN-IM-2012-25149), and ten individuals from the Red Sea (not found in the MNHN collections). At least one of those specimens belongs to P. peronii because of the length of the spine of the accessory penial gland mentioned by Labbé as 6 to 7 mm. The specimens from Sumatra and the Seychelles were fully dissected by Labbé (the Sumatra individual is basically empty): the male parts are missing, and it is not possible to determine the type of intestinal loops. However, given their huge size, they most likely belong to P. peronii . The presence of P. peronii in the Red Sea is possible but, at this stage, questionable: the size mentioned by Labbé for those specimens (17/12 mm) strongly suggests that he did not examine P. peronii from the Red Sea. Those specimens from the Red Sea identified as P. peronii by Labbé could not be located at the MNHN (there are no specimens collected by Clot-Bey in the collections, and there are too many jars of specimens collected by Jousseaume to determine which jar corresponds to the species description in Labbé’s monograph).

Labbé’s (1934a: 191-192, figs 4-7) re-description of P. tongana was based on one individual from Djibouti (Obock), one individual (85/60 mm) from the Seychelles (MNHN-IM-2012-25148), two individuals from New Ireland, and one individual from Tonga which happens to be part of the type series by Quoy and Gaimard (MNHN-IM-2000-22937) even though Labbé does not mention it. The specimen from the Seychelles was re-examined for the present study and, given its huge size, it is confirmed that it belongs to P. peronii : its intestinal loops are of type I, with a transitional loop at 3 o’clock; the male parts are missing. There are two specimens (60/50 mm) from New Ireland at the MNHN which could potentially be the two specimens mentioned by Labbé, but the collecting dates do not match. At any rate, it does not matter much since our fresh specimens demonstrate that P. peronii is present in New Ireland (Fig. 6 ). The specimen from Obock could not be traced back at the MNHN; there is a specimen (80/60 mm) which could possibly correspond to it but it is a problematic specimen as it could also be a type specimen for P. gaimardi , and is now an empty notum (see below, remarks on the type material of P. gaimardi in P. verruculata ). Thus, the presence of P. peronii in Djibouti is not accepted here and would need to be supported by positive evidence.

Risbec (1935: 415) illustrated the eggs of an onchidiid individual from New Caledonia which he called " Oncidium tonga Q et G," clearly a spelling mistake for Onchidium tonganum Quoy & Gaimard, 1832. It is not possible to know what species Risbec was referring to because there are three Peronia species in New Caledonia (Fig. 6 ).

White (1951: 241) reported a single specimen (53/38 mm) of Onchidium peronii from the Persian Gulf. The radular formula (88 × 88-1-88) is not enough to identify a Peronia species. White’s record referred either to P. verruculata (unit #4) or P. madagascariensis (Fig. 6 ).

In Japan, Baba (1958: 144) indicated that some specimens of Onchidium verruculatum from Tokara Islands, south of Kyushu (ca. 30°N) are very large (up to 120 mm long), suggesting that P. peronii is found there, which would be its most northern record.

Macnae and Kalk (1958: 34, 44, 128) mentioned Onchidium peronii from Inhaca Island, Mozambique (ca. 26°S). Given that no information is provided for species identification, this record is not taken for granted. Onchidium peronii was likely confused with P. verruculata (unit #5), which our material indicates is present in Inhaca, or even P. madagascariensis , known from South Africa to western India (Fig. 6 ). The fact that the slugs were found on sand ( Macnae and Kalk 1958: 128) could suggest that they saw P. verruculata (unit #5).

Solem (1959: 39) did not report any new material or localities for P. peronii . The references that he mentioned (e.g., Bretnall 1919; Hoffmann 1928) are already commented on above. His proposed distribution ("from the Red Sea and Mauritius to New Caledonia, Samoa, and the Marshall Islands") is not fully accurate because it is based on the assumption that people never made any mistakes when identifying P. peronii , which is unfortunately not true. Solem (1959: 38) mentioned what he thought were the three "most obvious" of the "numerous differences" between O. peronii and O. verruculatum : distribution of branchial plumes (dorsal gills) on the notum, relative position of the pneumostome and the anus, and relative width of the hyponotum and pedal sole. But those features vary among individuals and should not be used for species identification.

Marcus and Marcus (1960: 877) described Peronia peronii from the Maldives based on eight specimens. Given that they report a maximum animal length of 155 mm, a long (4.5 mm) spine of the accessory penial gland, as well as a retractor muscle inserting near the heart, there is little doubt that they did examine P. peronii (Table 4 ). Later, Marcus and Marcus (1970: 213) added that they observed a retractor muscle inserting near the nerve ring in another of their specimens from the Maldives, which also is compatible with our present observations: a vestigial retractor muscle was even observed here in P. peronii (Table 4 ). Some of the material examined from historical museum collections for the present work also came from the Maldives (ANSP 304860).

Webb et al. (1969: 107-112) described copulatory mechanisms in specimens they identified as O. peronii . It is unclear from where those specimens were, possibly South Africa. At any rate, given that they illustrate a spine of the accessory penial gland which is only 1.4 mm long ( Webb et al. 1969: 110, fig. 3), they did not examine individuals of P. peronii .

It is not possible to determine whether Marcus and Marcus (1970: 213) examined an individual of Peronia peronii from Madagascar because they do not provide the key features that characterize it. They could have seen a large individual of P. madagascariensis instead. Britton (1984: 183) merely mentioned the fact that Marcus and Marcus (1970) accepted only two valid species names ( P. peronii and P. verruculata ), which is not strictly exact because Marcus and Marcus (1970) did not address the nomenclatural status of P. tongana and did say that P. branchifera was close to P. verruculata but not that it was its synonym.

Patil and Kulkarni (2013) reported Onchidium peronii from Uran City, near Mumbai, India, but it is impossible to determine what species they saw (most likely it was P. madgascariensis or the unit #4 of P. verruculata , or both).

Many chemical studies have mentioned P. peronii in the past few decades. However, the name P. peronii was used arbitrarily. The individuals used for the extraction of natural products may not have been properly identified. Biskupiak and Ireland (1985) extracted peroniatriols from specimens identified as P. peronii from Guam. Peronia peronii is undeniably present in Guam. However, it is possible that P. verruculata (unit #1) could be present there as well. Pietra (1990: 145) mentioned peroniatriols in Peronia peronii from Micronesia where more than one species may be found. Arimoto et al. (1993) did not indicate where specimens of P. peronii and O. verruculatum were collected. In Japan, where the individuals used by Arimoto et al. (1993) possibly came from, there are four Peronia species which are all cryptic externally. Pietra (2002: 290) briefly cited peroniatriols in P. peronii based on the work by Arimoto et al. (1993). Finally, the antibacterial peptide extracted from individuals of Peronia peronii from the Persian Gulf ( Bitaab et al. 2015) was most likely extracted from individuals of either P. verruculata (unit #4), or P. madagascariensis , or both (Fig. 6 ). The same general remark applies to ecological studies: Morrisey et al. (2010: 72) listed (with no justification for species identification) the presence of Peronia peronii in mangroves of the estuary of the Mtata River (31°57'S), South Africa; most likely, Morrisey et al. (2010: 72) encountered P. madagascariensis instead.

Finally, a few last words on P. peronii in phylogenetic studies. Dayrat et al. (2011: 428) and White et al. (2011: 4) identified a specimen from Guam (CASIZ 180486) as Peronia peronii , which is specimen [443] in the present study (Fig. 2 ). The specimen tentatively identified as Peronia cf. peronii from Mozambique (NHMUK 20060414) by Dayrat et al. (2011: 428) belongs to P. madagascariensis , which is specimen [735] in the present study (Fig. 2 ). The DNA sequences of the specimen from Guam were used again in several studies (e.g., Gaitán-Espitia et al. 2013; Harasewych et al. 2015).

Figures

Figure 2. Phylogenetic relationships between Peronia species based on concatenated mitochondrial COI and 16 S DNA sequences. Numbers by the branches are the bootstrap values (maximum likelihood analysis) and the posterior probabilities (Bayesian analysis). Only the values> 50 % (ML) and> 0.9 (Bayesian) are indicated. Numbers for each individual correspond to unique identifiers for DNA extraction. Information on specimens can be found in the lists of material examined and in Table 2. The color used for each species or mitochondrial unit is the same as the color used in Figs 3 - 6.

Figure 6. Geographical distribution of the Peronia species A distribution of all Peronia species except for P. peronii B distribution of P. peronii. The colors are the same as those used in Figs 2 - 5. Colored areas correspond to hypothetical geographical ranges based on confirmed records only. Distinct colors are used for each unit of P. verruculata. The distribution of P. verruculata in the Indo-West Pacific is actually continuous. However, because it is unclear which units are present in regions from where we have no fresh material of P. verruculata (red areas), no unit of P. verruculata is shown there. For P. peronii, black dots correspond to material identified based on anatomical characters and blue dots correspond to material with DNA sequences. Details on species distribution can be found in each species description.

Figure 7. Habitat, Peronia peronii, Papua New Guinea, Madang, limestone rocky intertidal (st PM 12).

Figure 8. Live animals, Peronia peronii, Mauritius A dorsal view, 140 mm long [5872] (MNHN-IM- 2019 - 1605) B dorsal view, 125 mm long [5874] (MNHN-IM- 2019 - 1605) C ventral view, same as A; D ventral view, same as B.

Figure 9. Digestive system, dorsal view, Peronia peronii, type specimens. The arrow indicates the orientation of the transitional loop A paralectotype, Onchidium peronii, Timor (MNHN-IM- 2000 - 22938) B lectotype, Onchidium tonganum, Tonga (MNHN-IM- 2000 - 22937) C lectotype, Onchidium punctatum, Indonesia, West Papua (MNHN-IM- 2000 - 22966) D possible paralectotype, Paraperonia gondwanae, Mauritius (MNHN-IM- 2000 - 33686) E lectotype, Paraperonia fidjiensis, Fiji (MNHN-IM- 2000 - 33692). Scale bars: 5 mm (A, D), 10 mm (B, C, E). Abbreviations: ddg dorsal digestive gland, i intestine, pdg posterior digestive gland, st stomach.

Figure 10. Digestive system, dorsal view, Peronia peronii. The arrow indicates the orientation of the transitional loop A Mauritius [5874] (MNHN-IM- 2019 - 1605) B Papua New Guinea, Madang [5472] (MNHN-IM- 2013 - 14052) C Guam [5840] (MNHN-IM- 2019 - 1609). Scale bars: 10 mm (A-C). Abbreviations: ddg dorsal digestive gland, i intestine, pdg posterior digestive gland, st stomach.

Figure 11. Radula, Peronia peronii A-C Papua New Guinea [5476] (MNHN-IM- 2013 - 16260) D-H Guam [5840] (MNHN-IM- 2019 - 1609) A lateral teeth B rachidian and innermost lateral teeth C rachidian and innermost lateral teeth D rachidian and innermost lateral teeth E rachidian and lateral teeth F lateral teeth G lateral teeth, frontal view H outermost lateral teeth. Scale bars: 100 μm (A), 40 μm (B, D), 80 μm (C), 200 μm (E, F), 100 μm (G, H).

Figure 12. Radula, Peronia peronii, Mauritius [5872] (MNHN-IM- 2019 - 1605) A rachidian and innermost lateral teeth B rachidian and lateral teeth C outermost lateral teeth D lateral teeth. Scale bars: 40 μm (A), 100 μm (B), 20 μm (C), 200 μm (D).

Figure 13. Posterior, hermaphroditic (female) reproductive system, Peronia peronii A Mauritius [3605] (MNHN-IM- 2019 - 1606) B Papua New Guinea, Madang [5472] (MNHN-IM- 2013 - 14052). Scale bars: 10 mm (A), 5 mm (B). Abbreviations: dd deferent duct, fgm female gland mass, hg hermaphroditic gland, ov oviduct, rs receptaculum seminis, sp spermatheca.

Figure 14. Anterior, male, copulatory apparatus, Peronia peronii A Mauritius [3605] (MNHN-IM- 2019 - 1606) B Papua New Guinea, Madang [5472] (MNHN-IM- 2013 - 14052). Scale bars: 10 mm (A), 5 mm (B). Abbreviations: ag accessory penial gland, dd deferent duct, ms muscular sac, ps penial sheath, rm retractor muscle, v vestibule.

Figure 15. Penial hooks, Peronia peronii A Mauritius [5872] (MNHN-IM- 2019 - 1605) B Mauritius [3605] (MNHN-IM- 2019 - 1606) C, D Guam [5840] (MNHN-IM- 2019 - 1609). Scale bars: 6 μm (A, B, D), 40 μm (C).

Figure 16. Accessory penial gland spine, Peronia peronii A, B, F, G Mauritius C, D, H Papua New Guinea E, I Guam A [3605] (MNHN-IM- 2019 - 1606) B [5872] (MNHN-IM- 2019 - 1605) C [5471] (MNHN-IM- 2013 - 12500) D [5472] (MNHN-IM- 2013 - 14052) E [5840] (MNHN-IM- 2019 - 1609) F same as A; G same as B; H same as C; I same as E. Scale bars: 800 μm (A-D), 1 mm (E), 40 μm (F-I).