Onchidium applanatum Simroth, 1920: 294 Systematic revision of Platevindex Baker, 1938 (Gastropoda: Euthyneura: Onchidiidae) Goulding, Tricia C. Bourke, Adam J. Comendador, Joseph Khalil, Munawar Quang, Ngo Xuan Tan, Shau Hwai Tan, Siong Kiat Dayrat, Benoît European Journal of Taxonomy 2021 2021-03-08 737 1 1 133 872JJ (Simroth, 1920) Goulding & Bourke & Comendador & Khalil & Quang & Tan & Tan & Dayrat 2021 Simroth 1920 [487,964,735,762] Gastropoda Onchidiidae Platevindex GBIF Animalia Systellommatophora 77 78 Mollusca species applanatus comb. nov.   Figs 36–45      Onchidium applanatum Simroth, 1920: 294, pl. 20, figs 40–42.    Material examined   Holotype  INDONESIA• holotype(15/ 12 mm), by monotypy; Aru Inseln, Strand von Manumbai, Kobroor[Manumbai Beach, Kobroor Island, Aru Islands, Moluccas, Indonesia];  13 Mar. 1908; H. Mertonleg.; ZMB/Moll 104630.   Notes on typematerialThe notum of the holotypewas cut open for the present study to check internal characters; all organs remain in the specimen.   Other material  INDONESIA–  Ambon• 1 spec.(15/12 [2736] mm); Pulau Haruku; 03°36.520′ S, 128°25.068′ E;  11 Feb. 2014; station 127; dead log high on beach above rocky  Sonneratiamangrove; UMIZ 00100•  4 specs(22/15 [2754], 18/14 [2755], 18/14 [2757] and 15/12 [2750] mm); Passo; 03°37.080′ S, 128°16.068′ E;  13 Feb. 2014; station 129; logs on rocky beach with coral rubble; UMIZ 00101. –   Seram• 2 specs(24/20 [2877] and 17/11 [2880] mm); Piru; 03°04.072′ S, 128°11.362′ E;  19 Feb. 2014; station 136; beach of palms and  Acrostichumferns behind  Sonneratiamangrove; UMIZ 00090. –   Kei Islands• 6 specs(21/14 [2892], 17/11 [3563], 16/10 [2893], 16/10 [2895], 13/6 [2894] and 12/9 [2900] mm); Un; 05°38.273′ S, 132°45.738′ E;  23 Feb. 2014; station 137;   Bruguieraand  Rhizophoramangrove with coral rubble and thin layer of mud; UMIZ 00102•  1 spec.(15/9 [2904] mm); Un; 05°38.273′ S, 132°45.738′ E;  25 Feb. 2015; station 140; back of mangrove with rocks, mud, dead logs, and leaf litter; UMIZ 00103•  1 spec.(5/4 [2925] mm); Fiditan; 05°35.957′ S, 132°45.112′ E;  28 Feb. 2014; station 144; rocks with mat of algae behind dense  Rhizophoramangrove; UMIZ 00104. –   Sulawesi• 1 spec.(17/11 [2160] mm); Bahoi; 01°43.355′ N, 125°01.232′ E;  10 Mar. 2013; station 85; sand, rocks and pieces of wood outside a mangrove; UMIZ 00083.   MAURITIUS• 1 spec.(7/4 [3604] mm); Pointe Maurice; 20°15.447′ S, 57°47.670′ E;  8 Jun. 2014; station 174;   Rhizophoramangrove with very dark mud, slug under piece of wood; MNHN-IM-2019-1392•  1 spec.(9/7 [3152] mm); Mahebourg; 20°25.059′ S, 57°42.680′ E;  10 Jun. 2014; station 176; mangrove with dark brown mud, slugs on rotting petiole of palm frond; MNHN-IM-2019-1393•  1 spec.(7/5 [3442] mm); same collection data as for preceding; MNHN-IM-2019-1394.   Fig. 36.  Platevindex applanatus( Simroth, 1920) comb. nov., live animals. A. Dorsal view, 16 mm long [2893], Indonesia, Kei Islands (UMIZ 00102). B. Dorsal view, 16 mm long [2895], Indonesia, Kei Islands (UMIZ 00102). C. Dorsal view, 15 mm long [2904], Indonesia, Kei Islands (UMIZ 00103). D. Dorsal view, 16 mm long [3563], Indonesia, Kei Islands (UMIZ 00102). E. Dorsal view, 18 mm long [2757], Indonesia, Ambon (UMIZ 00101). F. Dorsal view, 5 mm long [2925], Indonesia, Kei Islands (UMIZ 00104). G. Ventral view, same as E. H. Ventral view, 12 mm long [2900], Indonesia, Kei Islands (UMIZ 00102). I. Dorsal view, 9 mm long [3152], Mauritius (MNHN-IM-2019-1393). J. Same as I. K. Ventral view, same as I.   PAPUA NEW GUINEA–  Madang• 1 spec.(14/11 [5437] mm); South Dumduman Island; 05°00.2′ S, 145°47.6′E;  9 Nov.2012; MNHNexpedition Papua Niuginileg.; station PM12; limestone rocky intertidal; MNHN-IM-2013-12493•  1 spec.(16/16 [5424] mm); Hargun Island; 05°01.6′ S, 145°47.9′ E;  15, 20 Nov.2012; MNHN expedition Papua Niugini leg.; station PM24; night tide; MNHN-IM-2013-14043•  1 spec.(13/11 [5450] mm); same collection data as for preceding; MNHN-IM-2013-14051•  1 spec.(18/15 [5420] mm); same collection data as for preceding; MNHN-IM-2013-13765•  1 spec.(13/11 [5457] mm); Wonad Island; 05°08.1′ S, 145°49.3′ E;  27 Nov. 2012, 9 Dec. 2012; MNHN expedition Papua Niugini leg.; station PM41; sandy beach and intertidal rocks; MNHN-IM-2013-15867•  1 spec.(13/10 [5462] mm); Tab Island; 05°10.2′ S, 145°50.4′ E;  28 Nov. 2012; MNHN expedition Papua Niugini leg.; station PM42; night tide, sandy beach and intertidal rocks; MNHN-IM-2013-15908. –   New Ireland• 1 spec.(7/4 [6094] mm); Povalval, E coast of New Ireland; 02°41′ S, 150°57′ E;  11–13 Jun. 2014; MNHN expedition Kavieng 2014 leg.; station KM05; mixed hard platform and seagrass bed at outlet of rivulet; MNHN-IM-2013-53534•  1 spec.(8/6 [6096] mm); Cape Jesehke, Manne Island; 02°43.1′ S, 150°37.8′ E;  15, 26 Jun.2014; MNHN expedition Kavieng 2014 leg.; station KM32;   Rhizophoramangrove; MNHN-IM-2013-54161•  1 spec.(10/7 [6097] mm); same collection data as for preceding; MNHN-IM-2013-54163•  1 spec.(8/6 [6098] mm); same collection data as for preceding; MNHN- IM-2013-54164.   VANUATU• 1 spec.(12/11 [5491] mm); Santo Rose Point; 15°34.9′ S, 167°02.4′ E;  10 Sep. 2006; MNHNexpedition Santo 2006 leg.; station VM02; intertidal, coral sand; MNHN-IM-2013-62402•  1 spec.(9/8 [5493] mm); same collection data as for preceding; MNHN-IM-2013-62404.    Description  Color and morphology of live animals( Fig. 36) Live animals are not covered with mud and their natural color can be seen without washing. The notum is bumpy with prominent, distinctly-raised papillae (with or without dorsal eyes). Live animals may become nearly hemispherical when disturbed. The dorsal color is variable although it is typically brown with yellow longitudinal (irregular) lines. Slugs with an entirely dark brown notum or a light beige notum also occur. The hyponotum is light grey and almost translucent in small specimens. The margin of the hyponotum is frequently translucent with the brown color of the notum showing through. The foot is light yellow. Papillae with dorsal eyes are present. Their exact number is difficult to determine, as they are often retracted, but ranges approximately from 4 to 26, except in the case of very small specimens, in which as few as 2 dorsal eyes have been observed. Each papilla bears one dorsal eye. Dorsal eyes may be distributed across the notum or only present in the middle but are always absent on the margin (i.e., eyes are never < 2 mmfrom the notum edge).  Digestive system( Figs 1C, 37–40) Radulae measure up to 4.3 mmin length. Examples of radular formulae are presented in Table 5. Due to the high genetic divergence (in COI sequences) between populations of  P. applanatus, radulae are figured from Indonesia, Mauritiusand Papua New Guinea( Figs 37–39). Intestinal loops are of typeI, with a transitional loop oriented between 1 and 2 o’clock ( Figs 1C, 40A–C).   Fig. 38.  Platevindex applanatus( Simroth, 1920) comb. nov., radula, Mauritius. A. Left, outermost, lateral teeth [3604] (MNHN-IM-2019-1392). B. Rachidian tooth and innermost lateral teeth, same as A. C. Rachidian tooth and left, innermost lateral teeth [3152] (MNHN-IM-2019-1393). D. Right, lateral teeth [3442] (MNHN-IM-2019-1394). Scale bars: A = 10 μm; B–D = 20 μm.  Reproductive system( Figs 41–44) In the posterior part of the reproductive system, the oviduct is wider than the deferent duct (up to twice as wide). Its distal section (distal to the spermatheca) is slightly longer than its proximal section (up to two or three times as wide) or equal to it in length. The deferent duct is longer than the oviduct, loosely attached to it, and varies from slightly convoluted with a few loose loops to tightly coiled with U-shaped loops ( Fig. 41). The position of the female pore varies from being adjacent to the anus to 4 mmaway from it in large specimens. The flexible, distal region of the penis with hooks measures approximately 1.5 to 3 mmin length. In eastern Indonesia, the distal region is 2 to 3 mmlong, while in Mauritiusand Papua New Guineait is approximately 1.5 to 2 mmlong. The penial hooks are large and can be seen inside the semi-transparent penis. They are usually 45 to 90 µmlong ( Figs 43, 44A), but between 20 to 60 µmin smaller specimens from Mauritius( Fig. 44B–C). The insertion of the penial retractor muscle varies. It inserts at the posterior end of the visceral cavity in specimens from eastern Indonesia, except in a few specimens in which it inserts approximately ¾ down the length of the visceral cavity. It inserts approximately halfway to ¾ down the length of the visceral cavity in specimens from Papua New Guinea(and near the posterior end of the visceral cavity in one specimen). In Mauritius, it inserts at the posterior end of the visceral cavity in the largest specimen, and by the heart halfway down the visceral cavity in a smaller specimen. The length of the retractor muscle varies from much shorter than the penial sheath ( 1/ 5to 1/ 3of its length) to as long as the penial sheath. The deferent duct is not particularly long and is only loosely convoluted ( Fig. 42). It may even be nearly straight in immature specimens ( Fig. 42C).   Fig. 39.  Platevindex applanatus( Simroth, 1920) comb. nov., radula, Papua New Guinea. A. Rachidian and innermost lateral teeth [5450] (MNHN-IM-2013-14051). B. Outer lateral teeth, same as A. C. Inner lateral teeth, same as A. D. Rachidian and innermost lateral teeth [5424] (MNHN-IM-2013-14043). Scale bars: A = 20 μm; B, D = 30 μm; C = 50 μm.  Distinctive diagnostic features( Table 4) Externally,  Platevindex applanatuscan be easily distinguished from  P. martensiand  P. aptei sp. nov.by the light yellow color of its foot. The presence of prominent dorsal papillae helps to distinguish  P. applanatusfrom other species of  Platevindex, except  P. luteus, which is characterized by similar prominent dorsal papillae. The dorsal coloration of  Platevindex applanatusis much more variable than in other species of  Platevindex, and this variation prevents reliable separation from  P. luteus. However, the dorsal notum of  P. applanatusis frequently marked by bright yellowish-green markings or bands, which were very rarely observed in  P. luteus. Individuals of  P. applanatusalso reach a smaller maximum size than individuals of  P. martensiand  P. amboinae, two species that are sympatric in eastern Indonesia, between the Halmahera Sea and the Banda Sea. However, animal sizes overlap between species and cannot be reliably used for identification.   Fig. 40.  Platevindex applanatus( Simroth, 1920) comb. nov., digestive system, intestinal loops of type I. A. Dorsal view, type I with a transitional loop oriented at 2 o’clock, Kei, Indonesia [2892] (UMIZ 00102). B. Dorsal view, type I with a transitional loop oriented at 2 o’clock, Mauritius [3152] (MNHN- IM-2019-1393). C. Dorsal view, type I with a transitional loop oriented at 1 o’clock, Papua New Guinea [5420] (MNHN-IM-2013-13765). D. Stomach, ventral view, same as C. Abbreviations: ddg = dorsal digestive gland; e = esophagus; i = intestine; oldg = opening of the lateral lobe of the digestive gland; pdg = posterior digestive gland; rg = rectal gland; st = stomach; st1 = stomach chamber 1; st2 = stomach chamber 2; st3 = stomach chamber 3; st4 = stomach chamber 4. Scale bars: A, D = 3 mm; B = 2 mm; C = 4 mm. Internally, the intestinal loops of  P. applanatus( typeI) distinguish it from all other species of  Platevindex. The only other species with intestinal loops of typeI is  P. luteus. However, the orientation of the transitional loop can be used to reliably distinguish  P. applanatus(between 1 and 2 o’clock) from  P. luteus(between 3 and 8 o’clock).  Platevindex applanatuscan also be distinguished from  P. luteusbased on reproductive anatomy. The deferent duct in the posterior reproductive system is more closely attached to the oviduct, longer and more highly coiled in  P. applanatusthan in  P. luteus. The distal region of the oviduct (distal to the spermatheca) is also longer in  P. applanatusthan in  P. luteus. Finally, the distal region of the penis with hooks is longer in  P. applanatus(up to 3 mm) than in  P. luteus(up to 1 mm). The insertion of the retractor muscle varies greatly within  P. applanatus(it may insert at the posterior end of the visceral cavity or near the heart), so this character does not help to reliably distinguish it from  P. luteus.   Distribution( Fig. 10A)  Indonesia: Ambon, Aru Islands ( typelocality), Kei Islands. Mauritius. Papua New Guinea: Madangand New Ireland. Vanuatu. All records are new, except for the typelocality.   Habitat( Fig. 45)   Platevindex applanatusis primarily found in the high intertidal, including on limestone, on rocks covered with a thin layer of algae. In the Kei Islands, individuals were found on rocks at the upper margin of the intertidal near a mangrove. In Ambon, individuals were found on logs very high in the intertidal, including at one locality that was not near any mangrove. In mangroves, individuals were typically   Fig.42.  Platevindex applanatus( Simroth,1920) comb.nov.,anterior reproductive system,male copulatory apparatus. A. Kei, Indonesia [2892] (UMIZ 00102). B. Mauritius [3152] (MNHN-IM-2019-1393). C. Mauritius [3604] (MNHN-IM-2019-1392). D. Papua New Guinea [5420] (MNHN-IM-2013-13765). Abbreviations: dd = deferent duct; ps = penial sheath; rm = retractor muscle; v = vestibule. Scale bars: A = 2 mm; B, D = 1 mm; C = 0.5 mm.   Fig. 43.  Platevindex applanatus( Simroth, 1920) comb. nov., penial hooks. Indonesia, Ambon [2757] (UMIZ 00101). Scale bars: A = 50 μm; B = 60 μm. collected on dead logs or tree trunks. In Mauritius, it was found in mangroves, on pieces of wood and wet petioles of palm leaves.  Platevindex applanatusis not found directly on mud.    Remarks   Onchidium applanatumwas originally described from the Aru Islands. Fresh material was collected from the Kei Islands, very close to Aru. The holotypeof  Onchidium applanatumis small (15/ 12 mm) but its flattened shape, the presence of a rectal gland and no accessory penial gland all indicate that it is a  Platevindexslug. The prominent papillae on its dorsal notum and its digestive system of type I are compatible with the species described here as well as  P. luteus. However, the retractor muscle of the holotypeof  O. applanatumis very long and inserts near the posterior end of the visceral cavity, which is only compatible with the species described here (in  P. luteus, the retractor muscle inserts near the heart). Therefore,  Platevindex applanatusis applied to the species described here from the Kei Islands and Ambon.   Fig. 44.  Platevindex applanatus( Simroth, 1920) comb. nov., penial hooks. A. Papua New Guinea [5424] (MNHN-IM-2013-14043). B–C. Mauritius [3152] (MNHN-IM-2019-1393). Scale bars: A = 30 μm; B = 10 μm; C = 60 μm.   Fig. 45.Habitats of  Platevindex applanatus( Simroth, 1920) comb. nov., Indonesia (A–C), Papua New Guinea (D–E) and Mauritius (F). A. Ambon, log behind a rocky mangrove in the very high intertidal, shaded by trees (station 127). B. Kei Islands, rocks with algae at the edge of the mangrove (station 137). C. Kei Islands, Un, rocks in the high intertidal behind a mangrove, surrounded by dry vegetation, algae growing on the rocks (station 137). D. Madang, Hargun Island, night tide (station PM24). E. New Ireland, Povalval, east coast of New Ireland, mixed hard platform and seagrass bed at outlet of rivulet (station KM05). F. Mahebourg, close up of rotting petiole of palm frond at margin of mangrove where juvenile onchidiids were found.  Hoffmann (1928: 84–85)and Labbé (1934: 225–226)considered that  Onchidium applanatumand  Onchidium tabularis Tapparone-Canefri, 1883were both junior synonyms of  Onchidium planatumQuoy & Gaimard, 1825.  Onchidium planatum, originally described from Guam, may not even refer to an onchidiid based on the brief written description. Two pieces of a notum were located recently at the MNHN which are part of the typeseries of  O. planatum(MNHN-IM-2000-33706). However, these are so poorly preserved that it is not possible to determine whether they were part of an onchidiid slug. Tapparone-Canefri’s (1883)description of  O. tabularisfrom Wokam, Aru Islands, does not mention the internal anatomy, and the typespecimens could not be located. As a result, both  Onchidium planatumand  Onchidium tabularisare considered here nomina dubia. Labbé’s (1934: 225–226)specimens identified as  O. planatumfrom Guam, New Caledoniaand Mauritius(as île de France) cannot belong to  P. applanatusor any other species of  Platevindexdue to the presence of a penial gland. 3051754350 1908-03-13 ZMB H. Merton Indonesia Aru Inseln Kobroor 77 78 ZMB/Moll 104630 1 holotype 3051754357 dead log high on beach above rocky Sonneratia mangrove 2014-02-11 UMIZ Indonesia -3.6086667 Pulau Haruku 1 128.4178 Pulau Haruku 77 78 UMIZ 00100 1 Ambon 3051754324 logs on rocky beach with coral rubble 2014-02-13 UMIZ -3.618 Passo 1 128.2678 77 78 UMIZ 00101 4 3051754305 beach of palms and Acrostichum ferns behind Sonneratia mangrove 2014-02-19 UMIZ -3.0678666 Piru 1 128.18936 77 78 UMIZ 00090 2 Seram 3051754322 Bruguiera and Rhizophora mangrove with coral rubble and thin layer of mud 2014-02-23 UMIZ -5.637883 Kei Islands 1 132.7623 77 78 UMIZ 00102 6 Kei Islands 3051754386 back of mangrove with rocks, mud, dead logs, and leaf litter 2015-02-25 UMIZ -5.637883 1 132.7623 77 78 UMIZ 00103 1 3051754411 rocks with mat of algae behind dense Rhizophora mangrove 2014-02-28 UMIZ -5.599283 Fiditan 1 132.75186 Fiditan 77 78 UMIZ 00104 1 3051754354 sand, rocks and pieces of wood outside a mangrove 2013-03-10 UMIZ 1.7225833 Bahoi 1 125.02053 77 78 UMIZ 00083 1 Sulawesi 3051754401 Rhizophora mangrove with very dark mud, slug under piece of wood 2014-06-08 Mauritius -20.25745 Pointe Maurice 1 57.7945 77 78 MNHN-IM-2019-1392 1 3051754338 mangrove with dark brown mud, slugs on rotting petiole of palm frond 2014-06-10 Mauritius -20.41765 Mahebourg 1 57.711334 77 78 MNHN-IM-2019-1393 1 3051754453 mangrove with dark brown mud, slugs on rotting petiole of palm frond 2014-06-10 Mauritius -20.41765 Mahebourg 1 57.711334 77 78 MNHN-IM-2019-1394 1 3051754359 limestone rocky intertidal 2012-11-09 MNHN Papua Niugini Papua New Guinea -5.0033336 South Dumduman Island 130 145.79333 79 80 MNHN-IM-2013-12493 1 Madang 3051754349 2015-11-20 MNHN Papua Niugini Papua New Guinea -5.0266666 Hargun Island 130 145.79834 79 80 MNHN-IM-2013-14043 1 Madang 3051754303 [189,1284,405,433] 2012-11-20 MNHN Papua Niugini Papua New Guinea -5.0266666 Hargun Island 130 145.79834 79 80 MNHN-IM-2013-14051 1 Madang 3051754344 2012-11-20 MNHN Papua Niugini Papua New Guinea -5.0266666 Hargun Island 130 145.79834 79 80 MNHN-IM-2013-13765 1 Madang 3051754374 sandy beach and intertidal rocks 27 Nov. 2012, 9 Dec. 2012 MNHN Papua Niugini Papua New Guinea -5.135 Wonad Island 130 145.82167 79 80 MNHN-IM-2013-15867 1 Madang 3051754325 night tide, sandy beach and intertidal rocks 2012-11-28 MNHN Papua Niugini Papua New Guinea -5.17 Tab Island 130 145.84 79 80 MNHN-IM-2013-15908 1 Madang 3051754381 mixed hard platform and seagrass bed at outlet of rivulet 2014-06-11 2014-06-13 2014-06-11 MNHN Kavieng Papua New Guinea -2.6833334 Povalval 1307 150.95 Povalval 79 80 MNHN-IM-2013-53534 1 New Ireland 3051754387 Rhizophora mangrove 2015-06-26 MNHN Kavieng Papua New Guinea -2.7183332 Manne Island 130 150.63 Cape Jesehke 79 80 MNHN-IM-2013-54161 1 New Ireland 3051754420 Rhizophora mangrove 2014-06-26 MNHN Kavieng Papua New Guinea -2.7183332 Manne Island 130 150.63 Cape Jesehke 79 80 MNHN-IM-2013-54163 1 New Ireland 3051754351 Rhizophora mangrove 2014-06-26 MNHN- Kavieng Papua New Guinea -2.7183332 Manne Island 130 150.63 Cape Jesehke 79 80 MNHN- IM-2013-54164 1 New Ireland 3051754312 intertidal, coral sand 2006-09-10 MNHN Vanuatu -15.581667 Santo Rose Point 128 167.04 79 80 MNHN-IM-2013-62402 1 3051754423 [189,1231,963,991] intertidal, coral sand 2006-09-10 MNHN Vanuatu -15.581667 Santo Rose Point 128 167.04 79 80 MNHN-IM-2013-62404 1