Marmaronchis vaigiensis (Quoy & Gaimard, 1825) Dayrat & Goulding & Khalil & Lozouet & Tan, 2018

Dayrat, Benoît, Goulding, Tricia C., Khalil, Munawar, Lozouet, Pierre & Tan, Shau Hwai, 2018, Systematic revision one clade at a time: A new genus of onchidiid slugs from the Indo-West Pacific (Gastropoda: Euthyneura: Pulmonata), Raffles Bulletin of Zoology 66, pp. 814-837 : 824-833

Marmaronchis vaigiensis (Quoy & Gaimard, 1825) new combination

( Figs. 5 , 6A, C, F , 7A, C, E , 8A–C, G , 10 )

Onchidium vaigiense Quoy & Gaimard, 1825: 429 ; Tapparone- Canefri, 1883: 213; Plate, 1893: 175–176, figs. 10, 79; Bretnall, 1919: 314–315; Hoffmann, 1928: 76; Dayrat, 2010: 88–101, figs. 1–7.

Paraoncidium vaigiense (Quoy & Gaimard, 1825) . Labbé, 1934a: 229–230, figs. 68–70.

Onchidium ambiguum Semper, 1880: 264 , pl. 19, figs. 4–5, 10, pl. 22, figs. 16–19; Semper, 1882: 265, 289. New synonym.

Onchidium steenstrupii Semper, 1882: 265–266 , pl. 20, fig. 5, pl. 21, figs. 22, 24; Plate, 1893: 176; Bretnall, 1919: 315; Hoffmann, 1928: 45; Labbé, 1934a: 222 [as O. streenstrupii , spelling mistake]. New synonym.

Onchidella steenstrupii (Semper, 1882) . Tapparone-Canefri, 1883: 213 [as Oncidiella steenstrupii ].

Onchidium leopoldi Labbé, 1934b: 70–73 , figs. 10A, 11B, 13, 15, 23, 26, 33–35, pl. I, fig. 4 [as Oncidium leopoldi ].

Onchidella maculata — Labbé, 1934b: 78–80, figs. 10, 13, 39, pl. I, fig. 7 [not of Plate, 1893; as Oncidiella maculata ].

Type localities. Onchidium ambiguum : ‘ Aibukit, Palaos’ [i.e., Palau], which is the locality of the lectotype designated here (see Type Materials below). Other localities mentioned by Semper for other former syntypes (now paralectotypes) are Singapore and Nicobar Islands. Palau is selected here as the type locality because Semper regarded the specimens from Singapore and Nicobar Islands to be part of a distinct variety (which he did not name) .

Onchidium leopoldi : ‘Pisang Eiland (Nouvelle-Guinée)’ [i.e., Pisang Island, Banda Islands, Maluku, Indonesia]. Pisang Island is not on the northwest coast of New Guinea ( Dayrat, 2010) but in the Banda Sea, west of Irian Jaya and south of Seram and Ambon.

Onchidium steenstrupii : ‘ Sambelang’ [i.e., Little Nicobar Island, Nicobar Islands], which is the locality of the lectotype designated here (see Type Materials below). Other localities mentioned by Semper for other former syntypes (now paralectotypes) are Pohnpei ( Caroline Islands, Micronesia) and New Guinea. In the original description, Semper (1882: 266) mentions the Nicobar locality as “Sambelang am Gangeshafen (4 Exemplare), an und in verfaulten Baumstämmen (Kopenhagener Museum, Expedition der Galathea),” [translation: 4 specimens, preserved at the Copenhagen Museum, collected on rotten logs, Ganges harbor, Sambelang, Galathea expedition]. There are four labels in the jar of the lectotype and one paralectotype ( ZMUC). Three labels can hardly be read. One label, however, says ‘ Oncidium steenstrupii Semper 1885 / Loc. Sambelang, Ganges Havn., Nicobarerne. Paa en raaden Traestamme / Legit. Rhrdt. Galathea. Datum. Januar-Febr. 1846’, [translation: collected on rotten logs, Ganges harbor, Sambelang, Nicobar Islands, by J. T. Reinhardt, Galathea expedition, January-February 1846], which perfectly matches the locality mentioned in Semper’s original description (Sambelang is an old name for Little Nicobar Island). The label of the jar with the two other paralectotypes from Nicobar ( ZMB 39041) says “ Sambelong , Nikobas’ , which refers to Sambelang , Little Nicobar Island . Ponape (Pohnpei, Caroline Islands, Micronesia) is not a type locality but there is no doubt that the paralectotypes from Pohnpei are the specimens examined by Semper because both the label and the original description refer to specimens from the Museum Godeffroy collected by Kubary from Ponape. Finally , it is not possible to know where exactly in New Guinea the other paralectotypes were collected from. In the original description, Semper (1882: 266) only mentions that Tapparone-Canefri sent him one specimen from New Guinea. One label for two paralectotypes from New Guinea says ‘ Neu-Guinea / Tapp’ . ( ZMB 39046b) while the label for the other two paralectotypes simply says ‘ Neu-Guinea’ ( ZMB 39046a). Note that Tapparone-Canefri (1883: 213) briefly mentions three localities for O. steenstrupii : Ponape; Sambelang , India; and Sorong , New Guinea. It is therefore possible that the specimen(s) examined by Semper came from Sorong , which is in West Papua, Indonesia (near the type locality of M. vaigiensis ). At any rate, it is considered here that these paralectotypes could have been collected anywhere in New Guinea ( West Papua and Papua New Guinea), which is vague but falls within the known distribution of M. vaigiensis . Even though it is unclear whether or not Semper examined all four New Guinea paralectotypes for the purpose of the original description—he may have mentioned only one specimen instead of four by mistake, or he may have identified some specimens from New Guinea as O. steenstrupii after the publication came out—they are all part of Marmaronchis and they are all regarded as paralectotypes here .

Onchidium vaigiense : ‘ Îles Vaigiou et Rawak’ [i.e., Waigeo and Rawak islands , northwest of Irian Jaya, West Papua, Indonesia] .

Type materials. Onchidium ambiguum: The material examined by Semper for the original description of Onchidium ambiguum included 15 specimens: six specimens from Palau, eight from Singapore, and one from Nicobar. Semper (1882: 265) regarded the specimens from Singapore and Nicobar as a distinct variety (unnamed) of the species. A total of 10 syntypes were found in various collections, six from Singapore and four from Palau, all of which were examined for the present study and all of which look externally like M. vaigiensis . One of the specimens from Palau is designated here as a lectotype: 12/ 10 mm ( ZMB 39024a). The three other specimens from Palau are paralectotypes: 14/10, 12/8, and 12/ 10 mm ( ZMB 39024b). All specimens from Singapore are paralectotypes: four specimens 16/10, 11/8, 10/9, and 10/ 7 mm ( ZMB 39044), one specimen 10/ 8 mm ( ZMUC), and one specimen 12/ 10 mm ( NHMUK 80.10.8.7). The lectotype was left entire by Semper and was opened for the present study to check the characters diagnostic of Marmaronchis : intestinal loops of type I, rectal gland present, and accessory penial gland present. The three paralectotypes from Palau were dissected (likely by Semper) prior to the present study. Internal parts are partly or completely missing. The ZMUC paralectotype from Singapore was opened (by Semper or Hoffmann) prior to the present study and internal organs are mostly destroyed. Two ZMB paralectotypes (16/10 and 10/ 9 mm) from Singapore were opened (likely by Semper) prior to the present study and some internal organs are missing. Two ZMB paralectotypes (11/8 and 10/ 7 mm) from Singapore were opened for the present study to check the characters diagnostic of Marmaronchis . Finally , the NHMUK paralectotype from Singapore still is entire and was not dissected for the present study .

Onchidium leopoldi : Remarks on the type material of O. leopoldi , composed of three syntypes (20/17, 13/11, and 11/ 9 mm) in the collections of the Royal Belgian Institute of Natural Sciences ( RBINS, no catalog number), can be found in Dayrat (2010).

Onchidium steenstrupii: According to the original description, the material examined by Semper (1882: 266) for Onchidium steenstrupii included eight specimens: four specimens from Nicobar Islands, three from Ponape (Pohnpei, Caroline Islands, Micronesia), and one from New Guinea. A total of 10 syntypes were found in various collections (four from Nicobar , two from Pohnpei , and four from New Guinea), all of which were examined for the present study and all of which look externally like M. vaigiensis . One specimen 18/ 16 mm from Nicobar is designated here as a lectotype ( ZMUC). The three other specimens from Nicobar are paralectotypes: two specimens 16/14 and 20/ 17 mm ( ZMB 39041) and one specimen 18/ 15 mm ( ZMUC). The two specimens (20/16 and 17/ 12 mm) from Pohnpei are paralectotypes ( ZMH 27481/3). The vial with the two Pohnpei paralectotypes includes a third specimen which actually is a nudibranch. Finally, the four specimens from New Guinea are paralectotypes: 18/15 and 18/ 15 mm ( ZMB 39046a) and 15/12 and 11/ 10 mm ( ZMB 39046b). The ZMUC lectotype was dissected (likely by Semper) prior to the present study but we could still check all the characters diagnostic of Marmaronchis : intestinal loops of type I, rectal gland present, and accessory penial gland present. The ZMUC paralectotype from Nicobar is entire and was not dissected for the present study. One ZMB paralectotype (16/ 14 mm) from Nicobar was completely destroyed (likely by Semper) prior to the present study and all internal parts are missing. The second ZMB paralectotype (20/ 17 mm) from Nicobar was dissected (likely by Semper) prior to the present study but we could still check all the characters diagnostic of Marmaronchis . One ZMUC paralectotype from Nicobar was dissected (likely by Semper) prior to the present study but internal organs remain in the vial. One ZMH paralectotype (20/ 16 mm) from Pohnpei was dissected for the present study; the second ZMH paralectotype (17/ 12 mm) is still entire and was not dissected here. The 18/ 15 mm ZMB New Guinea paralectotype was dissected (likely by Semper) prior to the present study, but all organs remain inside the animal; the ZMB New Guinea paralectotype (15/ 12 mm) was dissected (likely by Semper) prior to the present study, and only pieces of the digestive gland and of the female reproductive system remain inside the specimen; two ZMB paralectotypes (18/15 and 11/ 10 mm) from New Guinea are still entire and were not dissected for the present study.

Onchidium vaigiense: The type material of O. vaigiense could not be located earlier ( Dayrat, 2009, 2010). At that time, the specimen that Labbé (1934a: 229–230, figs. 68–70) examined and thought was the type material of O. vaigiense could not be found either, and Labbé’s re-description of that specimen as Paraoncidium vaigiense was originally regarded as a misidentification because Labbé mentioned no accessory penial gland ( Dayrat, 2010: 88). In 2017, however, a specimen was located at the MNHN ( MNHN- IM- 33703) which likely is the specimen that Labbé described as Paraoncidium vaigiense , even though it is not a syntype of O. vaigiense (it is unclear how many type specimens were deposited at the MNHN for Quoy and Gaimard’s O. vaigiense ). The specimen MNHN-IM-33703 (14/ 12 mm) is extremely poorly preserved but its notum is smooth, as usual in M. vaigiensis . There is a recent label with the number ‘55’ (unknown meaning) and, as mentioned by Labbé, another label indicating ‘ Peronia Quoy et Gaimard, 1829 ’. However, and more importantly, there is a much older label, not mentioned by Labbé, on which one can read — though with some difficulty: ‘Vaigiou’ ‘Gaimard’ and ‘Astrolabe’. Those words strongly suggest that the specimen is part of the collection made during the voyage of the Astrolabe (1826–1829), which means that it cannot be the type material of O. vaigiense because the later was described based on collections made during the voyage of the Uranie and of the Physicienne (1817–1820). Most likely, that old label indicates that the specimen was identified as the ‘ Onchidium de Vaigiou’ and that it was collected by Quoy and Gaimard during the voyage of the Astrolabe (1826–1829) which visited places like New Ireland, Ambon, and Sulawesi, but not Waigeo Island. The specimen MNHN-IM-33703 could be part of M. vaigiensis but that is not certain. That being said, it probably does not matter whether MNHN-IM-33703 is part of M. vaigiensis or not given that no locality is known and that it cannot be considered to be part of the type material of O. vaigiense . Its digestive system is largely destroyed and the type of intestinal loops cannot be checked (Labbé says that it is of type I but he often made mistakes regarding the intestinal type). Its anterior male parts are missing and so the presence or absence of an accessory penial gland cannot be checked. Finally, a thin rectal gland seems to be present. If we trust that the intestinal type was of type I and that the rectal gland is present, then the specimen MNHN-IM-33703 likely is part of M. vaigiensis , assuming that Labbé—as often—made a mistake when he reported no penial accessory gland. Indeed, the only onchidiids with an intestinal type I, a rectal gland, and no penial accessory gland are a few Platevindex species and that specimen is not a Platevindex (its body is not flattened). There are two other jars with old Marmaronchis specimens in the MNHN collections, both labeled as ‘ Onchidium / Nouvelle-Irlande [New Ireland] 1829 / Mrs Quoy et Gaimard’. One jar labeled with the number ‘45’ contains two specimens (20/15 and 15/ 15 mm). The other jar labeled with the number ‘47’ contains two specimens (20/15 and 16/ 15 mm). These four specimens clearly are part of Marmaronchis , even though it cannot be determined whether they are part of M. vaigiensis or M. marmoratus . They apparently have not been used either by Quoy & Gaimard (1832–1833) or by Labbé (1934a). It is possible that the specimen MNHN-IM-33703 came from the same series of specimens from New Ireland and was identified by Quoy and Gaimard as what they called earlier the ‘ Onchidium de Vaigiou’.

Additional material examined. Singapore, North Coast, Admiralty Road West, 01°27.071′N, 103°46.633′E, 1 specimen 15/8 [1183] mm, station 10, cemented wall under jetty ( ZRC.MOL.3007). Philippines, Guimaras Island, Iloilo Province, Buenavista City, Santa Rosario, [no coordinates], 1 specimen 12/10 [715] mm, shore below Bavani Resort ( UF 245715). Indonesia, Sulawesi, Bahoi, 01°43.355′N, 125°01.232′E, 1 specimen (8/6 [2224] mm), station 88, sand, small rocks, pieces of wood outside narrow coastal mangrove ( UMIZ 00182). Indonesia, Sulawesi, Wori, 01°36.06′N, 124°51.73′E, 3 specimens (8/ 7 mm [2243], 14/8 [2244], and 5/4 [2294] mm), station 90, old Avicennia , Sonneratia , Rhizophora mangrove forest with, rocks and dead logs ( UMIZ 00183). Indonesia, Sulawesi, Mantehage Island, 01°41.880′N, 124°46.741′E, 1 specimen (7/6 [2309] mm), station 91, Sonneratia at low intertidal and Rhizophora at high intertidal ( UMIZ 00184). Indonesia, Kei Islands, Un, 05°38.273′S, 132°45.738′E, 1 specimen (10/8 [2908] mm), station 140, back of mangrove, on rocks, on mud, inside logs, and under leaf litter ( UMIZ 00185). Indonesia, Bali, Gilimanuk, 08°10.259′S, 114°26.606′E, 4 specimens (23/17 [3081], 17/12 [3083], and 12/10 [3590] mm), station 155, from high intertidal with water pools and many mounds up to shore with sand and rocks ( UMIZ 00186). Indonesia, Halmahera, Foli, 01°14.66′N, 128°10.61′E, 3 specimens (18/15 [5046], 19/12 [5153], and 24/15 [5154] mm), station 217, rocky shore near a beach ( UMIZ 00187). Papua New Guinea, Madang, Rempi Area, S Dumduman Island, 05°00.2′S, 145°47.6′E, 1 specimen (11/9 [5434] mm), leg. MNHN expedition Papua Niugini, station PM 11, brackish stream mouth near ocean ( MNHN IM- 2013-11717). Papua New Guinea, Madang, Rempi Area, S Dumduman Island, 05°00.2′S, 145°47.6′E, 1 specimen (16/11 [5435] mm), leg. MNHN expedition Papua Niugini, station PM 11, brackish stream mouth near ocean ( MNHN IM- 2013-11718). Papua New Guinea, Madang, Rempi Area, S Dumduman Island, 05°00.2′S, 145°47.6′E, 1 specimen (17/13 [5403] mm), leg. MNHN expedition Papua Niugini, station PM 12, limestone rocky intertidal ( MNHN IM- 2013-12491). Papua New Guinea, Madang, Rempi Area, SW Hargun Island, 05°01.6′S, 145°47.9′E, 1 specimen (21/18 [5406] mm), leg. MNHN expedition Papua Niugini, station PM 24, limestone rocky intertidal ( MNHN IM- 2013-14040). Papua New Guinea, Madang, Riwo waters, 05°08.9′S, 145°48.2′E, 1 specimen (8/7 [5463] mm), leg. MNHN expedition Papua Niugini, station PM 40, sandy beach and intertidal rocks ( MNHN IM- 2013-15566). Papua New Guinea, New Ireland, Nusalomon Island, 02°37.3′S, 150°40.4′E, 1 specimen (17/15 [6091] mm), leg. MNHN expedition Kavieng 2014, station KM 20, intertidal platform, sand and blocks ( MNHN IM- 2013- 54460). Papua New Guinea, New Ireland, Nusalomon Island, 02°37.3′S, 150°40.4′E, 1 specimen (5/3 [6100] mm), leg. MNHN expedition Kavieng 2014, station KM 20, intertidal platform, sand and blocks ( MNHN IM- 2013-54467). Papua New Guinea, New Ireland, Nusalomon Island, 02°37.3′S, 150°40.4′E, 1 specimen (7/5 [6099] mm), leg. MNHN expedition Kavieng 2014, station KM 20, intertidal platform, sand and blocks ( MNHN IM- 2013-54463). Vanuatu, Santo Rose Point, 15°34.9′S, 167°02.4′E, 1 specimen (15/13 [5486] mm), leg. MNHN expedition Santo 2006, station VM02, intertidal, coral sand ( MNHN IM- 2013-62408). Vanuatu, Santo Rose Point, 15°34.9′S, 167°02.4′E, 1 specimen (14/11 [5487] mm), leg. MNHN expedition Santo 2006, station VM02, intertidal, coral sand ( MNHN IM- 2013-62409). Vanuatu, Santo Rose Point, 15°34.9′S, 167°02.4′E, 1 specimen (15/14 [5490] mm), leg. MNHN expedition Santo 2006, station VM02, intertidal, coral sand ( MNHN IM- 2013- 62401). Vanuatu, W Mavéa Island, 15°22.4′S, 167°13.0′E, 1 specimen (15/14 [5489] mm), leg. MNHN expedition Santo 2006, station FM 36, intertidal ( MNHN IM- 2013-62418).

Distribution ( Fig. 9 ). Nicobar Islands (type locality of Onchidium steenstrupii , new synonym; Semper, 1880, as O. ambiguum , new synonym). Singapore ( Semper, 1880, as O. ambiguum , new synonym; Dayrat, 2010; present study). Indonesia: Ambon ( Dayrat, 2010); Bali (present study, new record); Banda Islands (type locality of O. leopoldi ); Halmahera ( Dayrat, 2010; present study); Kei Islands ( Dayrat, 2010; present study); Sulawesi (present study, new record); West Papua (type locality of O. vaigiense ; Dayrat, 2010). Philippines ( Hoffmann, 1928; Dayrat, 2010; present study). Palau (type locality of O. ambiguum , new synonym). Micronesia: Pohnpei (Semper, 1882, as O. steenstrupii , new synonym). Papua New Guinea: Madang ( Dayrat, 2010; present study); New Ireland (present study). Vanuatu (present study, new record). Note that the records of O. vaigiense in Madang, New Britain, and New Ireland ( Dayrat, 2010) as well as New Hanover ( Plate, 1893, Dayrat, 2010) could refer to M. vaigiensis or M. marmoratus , given the close proximity of New Hanover and New Britain to New Ireland and Madang (and given that M. vaigiensis and M. marmoratus are sympatric in New Ireland and Madang).

Habitat ( Fig. 10 ). Marmaronchis vaigiensis lives in the rocky intertidal, on rocks near a beach or not, mixed with sand or not. It can also be found on cemented, human-made structures, such as bridges, ditches, and retaining walls. It is not specifically associated with mangroves, but it can be found on rocks near mangroves. Occasionally, it can be found on tree trunks on the shore (e.g., station PM24, Madang, Papua New Guinea; Fig. 10H ). Rocks usually are covered by a thin algal mat. Marmaronchis vaigiensis can be locally abundant but its presence is less predictable than other onchidiids. It may not always be found even though a habitat may seem perfect for it, and weather conditions seem to matter as well ( Dayrat, 2010).

Remarks. The year 1824 adopted as the publication date for Onchidium vaigiense by all authors so far ( Bretnall, 1919; Hoffmann, 1928; Labbé, 1934a; Dayrat, 2009, 2010) is erroneous. According to collations of Quoy and Gaimard’s Zoology of the Uranie and Physicienne voyage (1817–1820), page 429 was part of a section published in 1825 ( Sherborn & Woodward, 1901: 392). The publication dates of the various sections of the volume on Landmollusken by Carl Semper in the Reisen im Archipel der Philippinen series were clarified by Johnson (1969). The combination Onchidium ambiguum was first published by Semper in 1880, with a part of the written description (p. 264) and all illustrations (plates 19 and 22). The end of the written description (p. 265) was printed only in 1882. The combination Onchidium steenstrupii was first published by Semper in 1882, with the complete written description and the illustrations on plate 21. The illustration of O. steenstrupii on plate 20 (figure 5) was published in 1880. However, the species name used by Semper in 1880 in the caption for figure 5 (plate 20) was ‘ Onchidium ambiguum ’, and he later indicated in his written description in 1882 that figure 5 (plate 20) actually referred to O. steenstrupii instead of O. ambiguum .

It cannot be determined whether the lectotype —designated in the present study—of Onchidium ambiguum from Palau (ZMB 39024a) is part of Marmaronchis vaigiensis or M. marmoratus because both species are cryptic anatomically. However, given that M. vaigiensis is geographically distributed from Singapore all the way to Vanuatu and the Philippines while M. marmoratus is restricted to a much smaller geographical area (New Ireland and Madang), it is decided here that the lectotype of O. ambiguum from Palau is part of M. vaigiensis , and that, as a result, O. ambiguum is a junior synonym of M. vaigiensis . Unfortunately, this cannot be confirmed here because we did not have access to freshlycollected specimens of Marmaronchis from Palau. It naturally cannot be completely excluded that it is M. marmoratus that is found in Palau (instead of M. vaigiensis ), in which case O. ambiguum would just become a junior synonym of M. marmoratus . Semper (1882: 289) briefly commented that Quoy & Gaimard’s Onchidium vaigiense may be identical to his O. ambiguum . Semper’s original description of the anatomy of O. ambiguum perfectly matches the anatomy of M. vaigiensis (e.g., penis with a cartilaginous tube and a distal portion bearing hooks approximately 70 μm in length, retractor muscle in front of the pericardium). Semper (1882: 265) thought that the specimens from Singapore and Nicobar were a variety with a higher number of dorsal eyes of the species while the typical species from Palau displayed a lower number of dorsal eyes. A higher number of dorsal eyes was also found in one Singapore individual by Dayrat (2010: 91) but the number of clusters of dorsal eyes varies from one to ten within the species. Bretnall (1919: 314) briefly mentioned O. ambiguum , which he regarded as valid even though he pointed out that Semper thought that O. ambiguum may be the same as Quoy & Gaimard’s O. vaigiense . Bretnall summarised Semper’s description and recorded O. ambiguum from Dunk Island, Queensland (17°56′S). Given that Bretnall did not describe the internal anatomy of the specimen from Queensland, it is unclear whether his record can be taken for granted. In fact, our team has spent four weeks exploring mangroves on the coast of Queensland, collecting gastropods from 29 stations from 16° to 21° S, and we did not find any M. vaigiensis there. That being said, we may have missed it and M. vaigiensis may be present in Queensland, even though it is questionable at this stage. Hoffmann (1928: 46) briefly described and commented on O. ambiguum , based on one specimen from Singapore (which he found in the ZMUC collections) and four specimens from Mindanao, Philippines (which he found in the Stockholm collections). The specimen he examined from the ZMUC collection (16 mm long) likely was not the ZMUC paralectotype (10/ 8 mm). Regardless, the fact that he mentions that a rectal gland is missing suggests that he misidentified O. ambiguum , which is surprising given that he supposedly had access to the ZMUC paralectotype of O. ambiguum . Finally, Labbé (1934a: 224) regarded O. ambiguum as valid, which he recorded from Palau, Singapore, Mindanao, Nicobar, and Samar ( Philippines). Samar was not mentioned by earlier authors and there is no way to determine whether Labbé’s record was correct or not (he did not comment on the anatomy or morphology of any specimens). At any rate, based on what we know about the distribution of M. vaigiensis ( Fig. 9 ), it is very likely present in Samar.

It cannot be determined whether the lectotype —designated in the present study—of Onchidium steenstrupii from Nicobar Islands (ZMUC) is part of Marmaronchis vaigiensis or M. marmoratus because both species are cryptic anatomically. However, given that M. vaigiensis is geographically distributed from Singapore all the way to Vanuatu and the Philippines while M. marmoratus is restricted to a much smaller geographical area (New Ireland and Madang), it is decided here that the lectotype of O. steenstrupii from Nicobar Islands is part of M. vaigiensis , and that, as a result, O. steenstrupii is a junior synonym of M. vaigiensis . Unfortunately, this cannot be confirmed here because we did not have access to freshly-collected specimens of Marmaronchis from Nicobar Islands. It naturally cannot be entirely excluded that the populations of Marmaronchis in Nicobar Islands are part of a third species restricted to the Bay of Bengal, in which case O. steenstrupii would just become a valid name. However, given the broad distribution of M. vaigiensis and given that many onchidiid species are shared between Singapore and the Bay of Bengal (e.g., Dayrat et al., 2017; Goulding et al., 2018b, c), it is assumed here that M. vaigiensis is present in Nicobar Islands (our team did not find it in the Andaman Island in 2011, but we may have missed it there). Semper (1882: 266) acknowledges that O. steenstrupii is externally very similar to O. ambiguum , but claims that their reproductive anatomy differs. However, the descriptions that he gives are similar and, most importantly, fit perfectly the anatomy of M. vaigiensis: Semper mentions that penial hooks (which he calls cartilaginous teeth) measure 70 μm in both O. steenstrupii and O. ambiguum , and the penial hooks of M. vaigiensis measure from 70 to 100 μm ( Table 4). Tapparone-Canefri (1883: 213) transferred O. steenstrupii to Onchidella with no justification and with no new material. Plate (1893: 176) agreed that Onchidium steenstrupii was very close to O. vaigiense but still regarded them as two different species, mostly based on differences in the dorsal colour and the foot width, which are traits that greatly vary between individuals. Bretnall (1919) regarded O. steenstrupii as valid without adding any new material. Hoffmann (1928: 45) examined the two specimens of O. steenstrupii preserved at the ZMUC (now the lectotype and a paralectotype) and mentioned O. steenstrupii as a valid species. Finally, Labbé (1934a: 222) described some specimens from the Philippines as O. steentrupii which seem to match the characteristics of M. vaigiensis (intestinal loops of type I, rectal gland present, accessory penial gland present) even though Labbé’s descriptions are always questionable. At any rate, M. vaigiensis is known to be present in the Philippines, regardless of Labbé’s records. Labbé suggested—with a question mark—that Mörch’s (1872: 325) ‘ Peronia mauritiana Blainville, 1824 ’ might be a misidentification of O. steenstrupii , but that seems unlikely because Mörch clearly refers to Gray’s (1850) illustrations of Peronia Fleming, 1822 .

The detailed comments on the type material of Onchidium leopoldi are not repeated here (see Dayrat, 2010). There is no doubt that O. leopoldi refers to a Marmaronchis species. Strictly speaking, however, it cannot be determined whether O. leopoldi refers to Marmaronchis vaigiensis or M. marmoratus because both species are cryptic anatomically. However, given that M. vaigiensis is known to be present (based on identification with DNA sequences provided here) in Sulawesi, Kei Islands, Bali, and Halmahera ( Fig. 9 ) and that the type locality of O. leopoldi (Banda Islands, in the Banda Sea, just south of Ambon) is surrounded by all those known localities of M. vaigiensis , it is confirmed here that O. leopoldi is a junior synonym of M. vaigiensis .

Dayrat (2010) examined the voucher specimen used by Labbé (1934b) to re-describe Onchidella maculata and there is no doubt that Labbé’s re-description was based on a misidentification. Dayrat (2010) assumed that Labbé examined a specimen that was part of O. vaigiense but it is not possible to know unequivocally whether that specimen is part of M. vaigiensis or M. marmoratus because both species are anatomically cryptic. However, that voucher specimen was collected in Manokwari, Irian Jaya, West Papua, very close to the type locality of M. vaigiensis (Waigeo and Rawak islands, Irian Jaya, West Papua) and it can reasonably be assumed that Labbé’s (1934b) specimen misidentified as O. maculata is part of M. vaigiensis .

Figures

Fig. 5. Live specimens, dorsal (A–H) and ventral (I–K) views, Marmaronchis vaigiensis, Indonesia. A, Bali, 23 mm long [3081] (UMIZ 00186); B, Bali, 17 mm long [3083] (UMIZ 00186); C, Halmahera, 18 mm long [5046] (UMIZ 00187); D, Halmahera, 19 mm long [5153] (UMIZ 00187); E, Kei, 10 mm long [2908] (UMIZ 00185); F, Sulawesi, 8 mm long [2224] (UMIZ 00182); G, Sulawesi, 8 mm long [2243] (UMIZ 00183); H, Sulawesi, 14 mm long [2244] (UMIZ 00183); I, same as A; J, same as C; K, same as H.

Fig. 6. Digestive system and reproductive system, Marmaronchis vaigiensis (A, C, F) and Marmaronchis marmoratus (B, D, E). A, Digestive system (type I), dorsal view, scale bar = 3 mm, Indonesia, Sulawesi [2244] (UMIZ 00183); B, Digestive system (type I), dorsal view, scale bar = 3 mm, Papua New Guinea, New Ireland, Kavieng [6092] (MNHN IM-2013-55527); C, Posterior reproductive parts, scale bar = 2 mm, same as A; D, Posterior reproductive parts, scale bar = 2 mm, same as B; E, Anterior male copulatory parts, scale bar = 2 mm, same as B; F, Anterior male copulatory parts, scale bar = 2 mm, Papua New Guinea, Madang [5435] (MNHN IM-2013-11718). Abbreviations: dd, deferent duct; ddg, dorsal lobe of digestive gland; fgm, female gland mass; hd, hermaphroditic duct; hg, hermaphroditic gland; i, intestine; ov, oviduct; pdg, posterior lobe of the digestive gland; ps, penial sheath; rg, rectal gland; rm, penial retractor muscle; rs, receptaculum seminis; sp, spermatheca; st, stomach; v, vestibule.

Fig. 7. Radula, Marmaronchis vaigiensis (A, C, E) and Marmaronchis marmoratus (B, D, F). A, Rachidian and innermost lateral teeth, scale bar = 10 μm, Indonesia, Bali [3081] (UMIZ 00186); B, Rachidian and innermost lateral teeth, scale bar = 10 μm, Papua New Guinea, New Ireland, Kavieng [6092] (MNHN IM-2013-55527); C, Right lateral teeth, scale bar = 20 μm, same as A; D, Right lateral teeth, scale bar = 20 μm, Papua New Guinea, Madang [5475] (MNHN IM-2013-15866); E, Outermost, left lateral teeth, scale bar = 20 μm, same as A; F, Left lateral tooth with basal lateral spine, outer lateral view, scale bar = 10 μm, same as D. Abbreviations: 1llt, first, left, lateral tooth; 1rlt, first, right, lateral tooth; 2llt, second, left, lateral tooth; 2rlt, second, right, lateral tooth; bls, basal lateral spine; hlt, hook of lateral tooth; mc, median cusp of rachidian tooth; rt, rachidian tooth.

Fig. 8. Spine of the accessory penial gland (A–F) and hooks of the penis (G, H), Marmaronchis marmoratus (A–C, G) and Marmaronchis vaigiensis (D–F, H). A, Scale bar = 100 μm, Papua New Guinea, New Ireland, Kavieng [6092] (MNHN IM-2013-55527); B, Spine tip, scale bar = 10 μm, same as A; C, Scale = 100 μm, Papua New Guinea, Madang [5413] (MNHN IM-2013-13352); D. Scale bar = 40 μm, Indonesia, Sulawesi [2244] (UMIZ 00183); E, Scale bar = 40 μm, Indonesia, Bali [3081] (UMIZ 00186); F, Scale bar = 40 μm, Papua New Guinea, New Ireland, Kavieng [6091] (MNHN IM-2013-54460); G, Scale bar = 10 μm, same as C; H, Scale bar = 10 μm, same as E.

Fig. 10. Habitats, Marmaronchis vaigiensis (A–H) and Marmaronchis marmoratus (H), Indonesia (A–E), Singapore (F), and Papua New Guinea (G, H). A, Halmahera, station 217 (UMIZ 00187); B, Same as A; C, Sulawesi, station 91 (UMIZ 00184); D, Kei, station 140 (UMIZ 00185); E, Bali, station 155 (UMIZ 00186); F, Singapore, station 10 (ZRC.MOL.3007); G, New Ireland, Kavieng, station KM20 (MNHN IM-2013-54460, -54467, -54463); H, Madang, station PM24 (MNHN IM-2013-13760, -15566).

Fig. 9. Geographic distribution of the two known species of the genus Marmaronchis. The red and dark blue dots correspond to the records for each species from the material included in the present study (the same colour are used on the phylogenetic trees represented in Figs. 1–4). The dark red dot (Ambon, Indonesia) corresponds to a record of Marmaronchis vaigiensis for an old specimen for which no DNA sequences was available (Dayrat, 2010). The four green dots corresponds to type localities of M. vaigiensis and its synonyms. The black dots correspond to paralectotypes of synonyms of M. vaigiensis. The yellow dot corresponds to the type locality of M. marmoratus. The many light blue dots correspond to regions where we collected gastropods in the past few years and where Marmaronchis was not found (acknowledging that it may have been missed in some of them). The orange dot (Guam) corresponds to a record of a Marmaronchis species (likely M. viagiensis) based on a picture and so it is not included within the species distribution area (see Discussion). Finally, the coloured areas correspond to hypothetical ranges based on known records.