Peronia platei (Hoffmann, 1928)

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 platei (Hoffmann, 1928) Figs 26 , 27 , 28 , 29 , 30 , 31 , 32

Onchidium platei Hoffmann, 1928: 51-53, figs 9, 10, pl. 3, figs 11, 12.

Type material.

Lectotype and paralectotypes. French Polynesia • lectotype, hereby designated, 18/10 mm; Eimeo [Moorea], Tahiti; 1851-1853; Eugenie Expedition leg.; st 1245-9, in the barrier reef; SMNH-Type-7537. • 2 paralectotypes, 16/10 mm and 16/10 mm; same collection data as for the lectotype; SMNH-Type-7537. • 4 paralectotypes, 17/10 mm, 16/12 mm, 15/11 mm, and 10/7 mm; Tahiti; Dec 1846; Reinhardt, Galathea Expedition 470 leg.; NHMD 613754. • 1 paralectotype, 7/5 mm; Tahiti; Reinhardt, Galathea Expedition 471 leg.; NHMD 613755. • 1 paralectotype, 15/10 mm; Tahiti; Reinhardt, Galathea Expedition 472 leg.; NHMD 613756.

Additional material examined.

Hawaii • 2 specimens 12/10 mm [706] and 12/12 mm [5380]; Molokai, Puko’o; 21°04.313'N, 156°48.001'W; 27 Jan 2003; V Bonito leg.; on rocks; UF 303653. • Oahu, Ala Moana Beach Park; 21°17.158'N, 157°50.827'W; 1 specimen 30/20 mm [6160]; 7 Oct 2018; TC Goulding leg.; st 264, intertidal rocks, night tide; BPBM 284527. • 1 specimen 30/20 mm [6161]; same collection data as for the preceding; BPBM 284528.

Papua New Guinea - Madang • 1 specimen 14/12 mm [5405]; Rempi Area, SW Hargun Island; 05°01.6'S, 145°47.9'E; 15 & 20 Nov 2012; MNHN Expedition Papua Niugini leg.; st PM24, night tide; MNHN-IM-2013-13762. • 1 specimen 20/17 mm [5412]; 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-2013-13351. • 1 specimen 12/10 mm [5410]; Riwo Waters; 05°08.9'S, 145°48.2'E; 26 Nov 2012; MNHN Expedition Papua Niugini leg.; st PM40, sandy beach and intertidal rocks; MNHN-IM-2013-15765. • 1 specimen 14/12 mm [5464]; Wonad Island; 05°08.1'S, 145°49.3'E; 27 Nov 2012; MNHN Expedition Papua Niugini leg.; st PM41, sandy beach and intertidal rocks; MNHN-IM-2013-15871.

Additional material examined

(historical museum collections). French Polynesia • 2 specimens 15/10 mm and 13/8 mm; Tuamotu Archipelago, NE side, Anaa Atoll; 17°20'S, 145°30'W; 27 Oct 1967; NGS-SBM Marquesa Expedition MV “Pele” 1967 leg.; WAM S26717. • 2 specimens 7/5 mm and 5/4 mm; Tuamotu Archipelago, Marutea Atoll; 17S, 143°10.02'E; Aug 1903; LG Seurat leg.; AM C.17073.

Hawaii • 15 specimens from 18/15 mm to 8/8 mm; Oahu, Kailua Bay, Mokapu Point; 21°28.02'N, 157°43.98'E; WF Ponder and EA Kay leg.; 7 Apr 1974; on rocks, semi-sheltered and exposed platforms; AM C.214245.

Kiribati • 8 specimens from 10/9 mm to 3/3 mm; Gilbert Islands, Apamama [Abemama]; 00S, 173E; 1917-1918; S Bock’s Pacific Expedition leg.; sand, inside lagoon; SMNH 106488.

Distribution

(Fig. 6 ). West Pacific: Papua New Guinea, French Polynesia (Tuamotu and Tahiti), Kiribati, and Hawaii. All records are new except for the type locality in Tahiti.

Etymology.

Peronia platei was named after German zoologist Ludwig Hermann Plate [1862-1937], professor of zoology at the University of Jena and author of a monograph on onchidiids ( Plate 1893).

Habitat.

Peronia platei is found primarily in the rocky intertidal. According to the label, specimens from Kiribati were collected on sand inside a lagoon ( P. sydneyensis and P. willani are also known to be found on sand).

Color and morphology of live animals

(Fig. 26 ). No picture of live animals was available for specimens from the West Pacific. The description of the color of live animals is based on Hawaii individuals. The dorsal notum is uniformly very dark grey, almost black, including papillae. The hyponotum is light yellowish. The foot is light yellowish to orange. The ocular tentacles are grey, like the head. The dorsal notum of live animals is covered by dozens of papillae of various sizes. Some papillae bear black dorsal eyes at their tip. The number of papillae with dorsal eyes is variable (from 7 to 10). The papillae with dorsal eyes cannot be counted in specimens from Hawaii because the notum is too dark and because eye pigmentation tends to fade in preservation. The largest specimens are 30 mm long in Hawaii and 20 mm in Papua New Guinea.

Digestive system

(Figs 27 , 28 ). Examples of radular formulae are presented in Table 5 . The median cusp of the rachidian teeth is approximately 30 to 35 μm long. The hook of the lateral teeth is approximately 60 to 90 μm long. The intestinal loops are of type V.

Reproductive system

(Figs 29 - 32 ). In the posterior (hermaphroditic) parts, the deferent duct and the oviduct are straight. In the anterior (male) parts, the muscular sac of the accessory penial gland is less than 5 mm long. 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 0.8 mm ([706] UF 303653) to 0.9 mm ([6161] BPBM 284528) in Hawaii and from 0.7 mm ([5405] MNHN-IM-2013-13762) to 1 mm ([5412] MNHN-IM-2013-13351) in Papua New Guinea. Its diameter at the conical base ranges from 95 to 100 μm (Hawaii) and from 65 to 80 μm (Papua New Guinea). Its diameter at the tip ranges from 25 to 30 μm (Hawaii) and from 20 to 30 μm (Papua New Guinea). The retractor muscle is shorter or longer than the penial sheath and inserts at the posterior end of the visceral cavity. Inside the penial sheath, the penis is a narrow, elongated, soft, hollow tube. Its distal end bears conical hooks which are less than 60 μm long in Hawaii and less than 20 μm long in Papua New Guinea.

Diagnostic features

(Table 4 ). Peronia platei is cryptic with P. setoensis . Both species share the same combination of anatomical traits: intestinal loops of type V, retractor muscle inserting at the posterior end of the visceral cavity, a spine of the accessory penial gland from 0.8 to 1 mm long ( P. platei ) and from 0.9 to 1.2 mm long ( P. setoensis ). The diameter of the spine of the accessory penial gland at its tip is larger in P. platei (25 to 30 μm) than in P. setoensis (less than 25 μm) but that may be simply due to limited sampling. Peronia platei and P. setoensis are both distributed in the West Pacific but they are not sympatric based on current data (Fig. 6 ).

Remarks.

Onchidium platei applies to the species described here because the anatomy of the lectotype is identical to the anatomy of our material (Table 4 ): gills on the dorsal notum; muscular sac of the accessory penial gland less than 5 mm long; spine of the accessory penial gland 0.9 mm long (observed by transparency); intestinal loops of type V; seven dorsal papillae with eyes. Our molecular analyses show that the species described here is widespread across the West Pacific, from Papua New Guinea to Hawaii. There is no reason to think that the populations in French Polynesia (type locality of O. platei ) are a distinct species. This, however, will have to be confirmed with fresh material from French Polynesia, preferably from Moorea, the type locality. All eight paralectotypes (also from Tahiti) also belong to the same species.

Hoffmann’s (1928: 51-53, figs 9, 10, pl. 3, figs 11, 12) original description, which is quite detailed, needs to be briefly commented on. Hoffmann mentions that dorsal gills are lacking but they are undoubtedly present in the lectotype and all paralectotypes (dorsal gills are often hard to see in preserved animals). The anatomical traits he describes agree with our observations on the type material. The intestinal loops, Hoffmann says, are of type I but slightly different from the regular type I due to the absence of a loop. Hoffmann calls it a type Ia. His illustration of it clearly represents a type V ( Hoffmann 1928: pl. 3, fig. 11). The spine of the accessory penial gland is 1 mm long and the retractor muscle attaches to the posterior end of the visceral cavity. According to Hoffmann (1928: 53), O. platei is most closely related to O. tumidum Semper, 1880 and O. nebulosum Semper, 1880 but differs from them based on the penis size. Onchidium tumidum was recently transferred to Paromoionchis ( Dayrat et al. 2019a), and O. nebulosum (type locality in Palau) applies to a Peronia species but is regarded here as a nomen dubium (see general discussion).

Additional specimens were found in historical museum collections which could be identified as P. platei mostly based on the intestinal loops of type V, the specimen size, and their geographic origin. Specimens from Kiribati (SMNH 106488) are especially interesting because they confirm the presence of specimens similar to P. platei far from Hawaii and Papua New Guinea, which strongly supports the assumption that P. platei is widespread across the entire West Pacific. Note that those specimens from Kiribati are not identified as P. setoensis (which is anatomically cryptic with P. platei ) because P. setoensis is found in much colder waters (33°N) in Japan (Fig. 6 ).

Labbé (1934a: 224) merely mentioned Onchidium platei as one of the valid Onchidium species names. Ruthensteiner (1997) briefly commented on the anatomy of the lung of Onchidium cf. branchiferum , based on specimens from Hawaii. Those were most likely specimens of Peronia platei , the only Peronia species found in Hawaii. Finally, note that the specimen [706] (UF 303653) was tentatively referred to as Peronia sp. 1 by Dayrat et al. (2011).

No Peronia slug from Hawaii was positively demonstrated to belong to P. verruculata (unit #1), which is characterized by intestinal loops of type I. Therefore, Hoffmann’s (1928: 44, 73) record of O. verruculatum from Hawaii is interpreted here as a misidentification of P. platei . Labbé (1934a: 193), Solem (1959: 39), and Marcus and Marcus (1970: 213) all assumed that P. verruculata was present in Hawaii based on Hoffmann’s (1928) study, without collecting or examining any new material.

Onchidella evelinae Marcus & Burch, 1965 was described based on small specimens (average length 6 mm) from Eniwetok Atoll, Marshall Islands (ca. 11°N, 162°E). The type material was deposited at the Museum of Zoology, University of Michigan, but could not be located there (personal communication from the collection manager, Dr. Taehwan Lee). Onchidella evelinae is a misidentification for one of the onchidiid species present in the Marshall Islands: it cannot refer to Onchidella slugs because an accessory penial gland is mentioned in the original description and because Onchidella is not present in the middle of the West Pacific. The Marshall Islands are within the distribution range of P. platei (Fig. 6 ), but a detail from the original description (the internal organs can be seen through the dorsal notum) suggests that O. evelinae does not refer to Peronia slugs because their notum is too thick for internal organs to be seen through it. Peronia peronii is also present in the Marshall Islands (Fig. 6 ), but, given the very small size of the specimens and that they were sexually mature, it is most unlikely that O. evelinae is a junior synonym of P. peronii (Fig. 6 ). The size of the spine of the accessory penial gland (1.3 mm) reported in the original description of O. evelinae is compatible with what is currently known (<1 mm) for P. platei (Table 4 ). Onchidella evelinae is regarded here as a new junior subjective synonym of Marmaronchis vaigiensis (Quoy & Gaimard, 1825): first, because internal organs can occasionally be seen through its thin notum (e.g., Dayrat et al. 2018: fig. 5E); second, because there are known records ( Dayrat et al. 2018: fig. 9) of M. vaigiensis in Pohnpei, Micronesia (ca. 6°N, 158°E), just a few degrees west of the Marshall Islands, and it is very possible that M. vaigiensis also is in the Marshall Islands. The size of the spine of the accessory penial gland (1.3 mm) reported in the original description of O. evelinae is higher than what is currently known for M. vaigiensis (<1 mm), but that trait does vary intra-specifically.

Figures

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 26. Live animals, Peronia platei, Hawaii, Oahu A dorsal view, 30 mm long [6161] (BPBM 284528) B dorsal view, 30 mm long [6160] (BPBM 284527) C ventral view, same as A; D ventral view, same as B.

Figure 27. Digestive system, dorsal view, Peronia platei, with intestinal loops of type V A lectotype, French Polynesia, Moorea (SMNH-Type- 7537) B Hawaii, Oahu [6160] (BPBM 284527) C Papua New Guinea, Madang [5412] (MNHN-IM- 2013 - 13351). Scale bars: 2 mm (A-C). Abbreviations: ddg dorsal digestive gland, i intestine, pdg posterior digestive gland, st stomach.

Figure 28. Radula, Peronia platei A Papua New Guinea, Madang [5405] (MNHN-IM- 2013 - 13762) B Hawaii, Oahu [6161] (BPBM 284528) C-E Hawaii, Molokai [706] (UF 303653) F [5380] (UF 303653) A right half rows of teeth B rachidian and innermost lateral teeth C rachidian and innermost lateral teeth D lateral teeth E outermost lateral teeth F lateral teeth. Scale bars: 200 μm (A), 20 μm (B, E), 30 μm (C), 100 μm (D), 80 μm (F).

Figure 29. Posterior, hermaphroditic (female) reproductive system, Peronia platei A Papua New Guinea, Madang [5412] (MNHN-IM- 2013 - 13351) B Hawaii, Oahu [6160] (BPBM 284527). Scale bars: 3 mm (A, B). Abbreviations: dd deferent duct, fgm female gland mass, hg hermaphroditic gland, ov oviduct, rs receptaculum seminis, sp spermatheca.

Figure 30. Anterior, male, copulatory apparatus, Peronia platei A lectotype, French Polynesia, Moorea (SMNH-Type- 7537) B Papua New Guinea, Madang [5412] (MNHN-IM- 2013 - 13351) C Hawaii [706] (UF 303653). Scale bars: 5 mm (A), 3 mm (B), 2 mm (C). Abbreviations: ag accessory penial gland, dd deferent duct, ms muscular sac, ps penial sheath, rm retractor muscle, v vestibule.

Figure 31. Penial hooks, Peronia platei A, C Hawaii, Oahu [6161] (BPBM 284528) B, D Papua New Guinea, Madang [5412] (MNHN-IM- 2013 - 13351). Scale bars: 40 μm (A), 20 μm (B), 10 μm (C), 2 μm (D).

Figure 32. Accessory penial gland spine, Peronia platei A-C, F, G Hawaii, Oahu D, E, H, I Papua New Guinea, Madang A [706] (UF 303653) B [6160] (BPBM 284527) C [6161] (BPBM 284528) D [5412] (MNHN-IM- 2013 - 13351) E [5405] (MNHN-IM- 2013 - 13762) F same as A; G same as B; H same as D; I same as E. Scale bars: 100 μm (A, E), 200 μm (B, D), 150 μm (C), 6 μm (F, H, I), 10 μm (G).