Peronia setoensis Dayrat & Goulding, 2020

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 setoensis Dayrat & Goulding sp. nov. Figs 33 , 34 , 35 , 36 , 37 , 38

Type material.

Holotype. Japan • holotype, hereby designated, 20/15 mm [5383]; Honshu, Wakayama, Nishimuro, near Seto Marine Biological Laboratory; 33°41.504'N, 135°20.179'E; 30 Aug 2014; R. Cumming leg.; exposed rock wall and platform; NSMT-Mo 78985.

Additional material examined.

Japan • 3 specimens 13/8 mm [5382], 10/5 mm [5384], and 12/10 mm [5385]; same collection data as for the holotype; NSMT-Mo 78986. • 2 specimens 15/10 mm [3753] and 15/10 mm [3754]; Honshu, Wakayama, Nishimuro, near Seto Marine Biological Laboratory; 33°41.533'N, 135°20.265'E; 2014; T Nakano leg.; NSMT-Mo 78987.

Additional material examined

(historical museum collections). Japan • 1 specimen 23/20 mm; Sagami Bay, Misaki; 1930-1931; Gislén’s Pacific Expedition 1930-1931 leg.; littoral rocky bottom; SMNH 180725.

Distribution

(Fig. 6 ). Endemic to subtropical waters of Japan: Honshu, Nishimuro, near Seto Marine Biological Laboratory (33N, type locality), Sagami Bay (35°N), and possibly Boso Peninsula, near Sagami Bay (35°N); Kyushu, Nagasaki, 32N ( Keferstein 1865a, b, as P. verruculata ).

Etymology.

Peronia setoensis is named after its type locality, near the Seto Marine Biological Laboratory: setoensis is a latinized adjective that agrees in gender (feminine) with the generic name ( ICZN 1999: Article 31.2).

Habitat

(Fig. 33 ). Peronia setoensis is found in the rocky intertidal. Few individuals are currently known but it may be discovered in additional localities in the future.

Color and morphology of live animals

(Fig. 34 ). The dorsal notum is greenish brown, light to dark, mottled with darker and lighter areas, occasionally with yellowish sides. The color of the dorsal papillae varies as that of the background itself. The ventral surface (foot and hyponotum) is yellowish or greyish 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. Some papillae bear black dorsal eyes at their tip. The number of papillae with dorsal eyes is variable (from 8 to 12). The largest specimens are 20 mm long.

Digestive system

(Figs 35A, B , 36 ). Examples of radular formulae are presented in Table 5 . The median cusp of the rachidian teeth is approximately 35 μm long. The hook of the lateral teeth is approximately 90 μm long. The intestinal loops are of type V.

Reproductive system

(Figs 35C, D , 37 , 38 ). 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 0.9 mm ([3754] NSMT-Mo 78987) to 1.2 mm ([3753] NSMT-Mo 78987). Its diameter at the conical base ranges from 80 to 85 μm. Its diameter at the tip ranges from 15 to 25 μm. The retractor muscle is shorter or longer than the penial sheath and inserts near the heart. Inside the penial sheath, the penis is a narrow, elongated, soft, hollow tube. Its distal end bears conical hooks which are less than 25 μm long.

Diagnostic features

(Table 4 ). Peronia setoensis is cryptic with P. platei . 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 0.9 to 1.2 mm long ( P. setoensis ) and from 0.7 to 1 mm long ( P. platei ). Peronia setoensis and P. platei are anatomically very similar to P. griffithsi , in which, however, the spine of the accessory penial gland is slightly shorter (less than 0.62 mm long). All three species are distributed in the West Pacific but Peronia setoensis is adapted to much colder waters than P. platei and P. griffithsi (Fig. 6 ).

Remarks.

A new species name is needed because no existing name applies to the species described here. A specimen from Sagami Bay (35°N), preserved in Stockholm (SMNH 180725), not included by Hoffmann (1928: 73) in his list of material for O. verruculatum , is identified here as P. setoensis because of its intestinal loops of type V (Table 4 ). This specimen indicates that P. setoensis is distributed on the eastern Pacific coast of Japan north of the type locality.

Keferstein (1865b) described as P. verruculata three slugs from Nagasaki, Kyushu, Japan (ca. 32°44'N). His written description ( Keferstein 1865b) was also based on an individual from Java but his figure captions clearly indicate that his drawings illustrated an individual from Nagasaki ( Keferstein 1865b: pl. VI, figs 14-16): Keferstein’s (1865b: pl. VI, fig. 16) drawing of the internal anatomy unmistakably illustrates intestinal loops of type V. Therefore, it is very likely that P. setoensis , the only one species of Peronia slugs with intestinal loops of type V in Japan, is also distributed in Kyushu. It is unclear whether Keferstein’s (1865a: pl. CII, figs 20*, 20**, pl. CV, figs 1, 2) drawings illustrate the same Nagasaki individual as the one with intestinal loops of type V ( Keferstein 1865b: pl. VI, fig. 16). It cannot be excluded that Keferstein examined several species found in Japan (Fig. 6 ). The Java individual cannot be identified.

The molecular data presented here indicate that there are four Peronia species in Japanese waters, but their geographic ranges need to be explored in better detail (Fig. 6 ). Peronia setoensis is definitely (our DNA sequences) present in southern Honshu (Wakayama Prefecture) and very likely in Kyushu based on Keferstein’s (1865b: pl. VI, fig. 16) drawing of intestinal loops of type V. Peronia verruculata (unit #1) is definitely (our DNA sequences) present in Wakayama Prefecture (ca. 33°N), southern Honshu, and is thus expected to be present in all Japanese waters south of Wakayama Prefecture. Also, Peronia verruculata is present in Sakurajima, Kyushu (ca. 31°N) and Okinawa (ca. 26°N) based on sequences that Takagi et al. (2019) recently published (see remarks on P. verruculata ). Peronia peronii is also present in Okinawa based on COI sequences that Takagi et al. (2019) recently published (see remarks on P. peronii ). And, finally, our new species P. okinawensis is only known from Okinawa so far.

Besides Keferstein (1865a, b), several authors mentioned onchidiids from Japan but, in most cases, species cannot be identified based on the limited information provided. Stimpson (1855: 380) described Onchis fruticosa based on slugs with dorsal gills from Kikaijima (28°30'N), between Kyushu and Okinawa, which could potentially belong to any of the four species present in Japanese waters. As a result, Onchis fruticosa is regarded as a nomen dubium (see general discussion).

Baba (1958) illustrated onchidiid slugs from three different places: Tokara Islands, just south of Kyushu (ca. 30°N); Amakusa, near Nagasaki, Kyushu (ca. 32°30'N); and Misaki, Osaka, Honshu (ca. 34°N). Baba (1958: 144) indicates that some specimens of Onchidium verruculatum from Tokara Islands were very large (up to 120 mm long), suggesting that P. peronii is found there, which would be its northernmost record (see remarks on P. peronii ). The smaller specimens that Baba (1958: 144) mentions from Tokara Islands could be a combination of P. verruculata (unit #1) and possibly P. setoensis . The two species which Baba (1958: 21) seems to distinguish (as Onchidium and Onchidium verruculatum ) in Misaki, near Osaka, could be P. verruculata (unit #1) and P. setoensis , which, based on our DNA sequences, are sympatric near the Seto Marine Laboratory, which is close to Osaka. And, finally, the slugs crawling on mud in Amakusa, near Nagasaki, are not Peronia slugs ( Baba 1958: 51) but most likely belong to Paromoionchis tumidus , a species which is present nearby, in Kumamoto Uki, as the COI sequences from the slugs of "Group I" in Takagi et al. (2019) cluster with our sequences of P. tumidus ( Dayrat et al. 2019a).

Katagiri and Katagiri (2007) distinguished two Peronia species (both as Onchidium verruculatum ) in the waters of the Boso Peninsula (near Sagami Bay, Honshu, ca. 35°N) based on external appearance and development. One species, called Isowamochi, is characterized by planktotrophic development, and the other, called Minneawamochi, by direct development. Most likely, these slugs belong to P. verruculata (unit #1) and P. setoensis , which are the only two Peronia species found north of 30N. However, this assumption would have to be confirmed with fresh collections and DNA sequences. Ueshima (2007) commented that the external distinction between the two species recognized by Katagiri and Katagiri (2007) is far more subtle and problematic, and he rightly suggested that molecular data could determine the relationships between those two species and P. verruculata (erroneously said to be from the Mediterranean). Note that Ueshima’s (2007) material, which covered a broad latitudinal range from the Kanagawa Prefecture (near Sagami Bay, ca. 35°N) all the way to Ishigaki Island (Okinawa, ca. 24°N), potentially included slugs from all four Peronia species found in Japan.

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 33. Habitat, Peronia setoensis, Japan, Honshu, near the Seto Marine Laboratory, type locality, exposed rock wall and platform.

Figure 34. Live animals, Peronia setoensis, Japan, Honshu A holotype, dorsal view, 20 mm long [5383] (NSMT-Mo 78985) B dorsal view, 10 mm long [5384] (NSMT-Mo 78986) C dorsal view, 12 mm long [5385] (NSMT-Mo 78986) D ventral view, same as A; E ventral view, same as B; F ventral view, same as C.

Figure 35. Peronia setoensis, Japan, Honshu A [3753] (NSMT-Mo 78987) B-D holotype [5383 H] (NSMT-Mo 78985) A digestive system, dorsal view, with intestinal loops of type V B digestive system, dorsal view, with intestinal loops of type V C posterior, hermaphroditic (female) reproductive system D anterior, male, copulatory apparatus. Scale bars: 2 mm (A-D). Abbreviations: ag accessory penial gland, dd deferent duct, ddg dorsal digestive gland, fgm female gland mass, hg hermaphroditic gland, i intestine, ms muscular sac, ov oviduct, pdg posterior digestive gland, ps penial sheath, rm retractor muscle, rs receptaculum seminis, sp spermatheca, st stomach, v vestibule.

Figure 36. Radula, Peronia setoensis, Japan, Honshu A-C holotype [5383 H] (NSMT-Mo 78985) D-F [3754] (NSMT-Mo 78987) G, H [3753] (NSMT-Mo 78987) A right half rows of teeth B rachidian and innermost lateral teeth C rachidian and lateral teeth D rachidian and innermost lateral teeth E lateral teeth F rachidian and lateral teeth G outermost lateral teeth H lateral teeth. Scale bars: 100 μm (A, H), 15 μm (B), 60 μm (C), 20 μm (D), 40 μm (E, F), 10 μm (G).

Figure 37. Penis and penial hooks, Peronia setoensis, Japan, Honshu A, B holotype [5383 H] (NSMT-Mo 78985) C, D [3753] (NSMT-Mo 78987) E, F [3754] (NSMT-Mo 78987). Scale bars: 40 μm (A), 4 μm (B), 100 μm (C), 2 μm (D, F), 20 μm (E).

Figure 38. Accessory penial gland spine, Peronia setoensis, Japan, Honshu A, C [3753] (NSMT-Mo 78987) B, D [3754] (NSMT-Mo 78987). Scale bars: 200 μm (A, B), 6 μm (C, D).