Platevindex applanatus ( Simroth, 1920 ) Goulding & Bourke & Comendador & Khalil & Quang & Tan & Tan & Dayrat, 2021

Goulding, Tricia C., Bourke, Adam J., Comendador, Joseph, Khalil, Munawar, Quang, Ngo Xuan, Tan, Shau Hwai, Tan, Siong Kiat & Dayrat, Benoît, 2021, Systematic revision of Platevindex Baker, 1938 (Gastropoda: Euthyneura: Onchidiidae), European Journal of Taxonomy 737 (1), pp. 1-133 : 78-88

Platevindex applanatus ( Simroth, 1920) 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. Merton leg.; ZMB/Moll 104630 .

Notes on type material The notum of the holotype was 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 Sonneratia mangrove; 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 Acrostichum ferns behind Sonneratia mangrove; 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; Bruguiera and Rhizophora mangrove 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 Rhizophora mangrove; 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; Rhizophora mangrove 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 .

PAPUA NEW GUINEA – Madang • 1 spec. (14/11 [5437] mm); South Dumduman Island ; 05°00.2′ S, 145°47.6′E; 9 Nov.2012; MNHN expedition Papua Niugini leg.; 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; Rhizophora mangrove; 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; MNHN expedition 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 mm from the notum edge).

Digestive system ( Figs 1C , 37–40 )

Radulae measure up to 4.3 mm in 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, Mauritius and Papua New Guinea ( Figs 37–39 ). Intestinal loops are of type I, with a transitional loop oriented between 1 and 2 o’clock ( Figs 1C , 40 A–C).

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 mm away from it in large specimens. The flexible, distal region of the penis with hooks measures approximately 1.5 to 3 mm in length. In eastern Indonesia, the distal region is 2 to 3 mm long, while in Mauritius and Papua New Guinea it is approximately 1.5 to 2 mm long. The penial hooks are large and can be seen inside the semi-transparent penis. They are usually 45 to 90 µm long ( Figs 43 , 44A ), but between 20 to 60 µm in smaller specimens from Mauritius ( Fig. 44 B–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 / 5 to 1 / 3 of 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 ).

Distinctive diagnostic features ( Table 4 )

Externally, Platevindex applanatus can be easily distinguished from P. martensi and P. aptei sp. nov. by the light yellow color of its foot. The presence of prominent dorsal papillae helps to distinguish P. applanatus from other species of Platevindex , except P. luteus , which is characterized by similar prominent dorsal papillae. The dorsal coloration of Platevindex applanatus is much more variable than in other species of Platevindex , and this variation prevents reliable separation from P. luteus . However, the dorsal notum of P. applanatus is frequently marked by bright yellowish-green markings or bands, which were very rarely observed in P. luteus . Individuals of P. applanatus also reach a smaller maximum size than individuals of P. martensi and 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.

Internally, the intestinal loops of P. applanatus (type I) distinguish it from all other species of Platevindex . The only other species with intestinal loops of type I 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 applanatus can also be distinguished from P. luteus based 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. applanatus than in P. luteus . The distal region of the oviduct (distal to the spermatheca) is also longer in P. applanatus than 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 (type locality), Kei Islands. Mauritius. Papua New Guinea: Madang and New Ireland. Vanuatu. All records are new, except for the type locality.

Habitat ( Fig. 45 )

Platevindex applanatus is 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

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 applanatus is not found directly on mud.

Remarks

Onchidium applanatum was originally described from the Aru Islands. Fresh material was collected from the Kei Islands, very close to Aru. The holotype of Onchidium applanatum is 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 Platevindex slug. 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 holotype of O. applanatum is 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 applanatus is applied to the species described here from the Kei Islands and Ambon.

Hoffmann (1928: 84–85) and Labbé (1934: 225–226) considered that Onchidium applanatum and Onchidium tabularis Tapparone-Canefri, 1883 were both junior synonyms of Onchidium planatum Quoy & 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 type series 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. tabularis from Wokam, Aru Islands, does not mention the internal anatomy, and the type specimens could not be located. As a result, both Onchidium planatum and Onchidium tabularis are considered here nomina dubia. Labbé’s (1934: 225–226) specimens identified as O. planatum from Guam, New Caledonia and Mauritius (as île de France) cannot belong to P. applanatus or any other species of Platevindex due to the presence of a penial gland.

Figures

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.

Fig. 37. Platevindex applanatus (Simroth, 1920) comb. nov., radula, Indonesia, Ambon. A. Rachidian and innermost lateral teeth [2754] (UMIZ 00101). B. lateral teeth with rachidian teeth, same as A. C. Lateral teeth [2755] (UMIZ 00101). D. Outermost lateral teeth, same as A. Scale bars: A, D = 30 μm; B = 50 μm; C = 100 μm.

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.

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.

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.

Fig. 41. Platevindex applanatus (Simroth, 1920) comb. nov., posterior reproductive system. A. Kei, Indonesia [2892] (UMIZ 00102). B. Mauritius [3152] (MNHN-IM-2019-1393). C. Papua New Guinea [5420] (MNHN-IM-2013-13765). Abbreviations: dd = deferent duct; fgm = female gland mass; hd = hermaphroditic duct; hg = hermaphroditic gland; ov = oviduct; rs = receptaculum seminis; sp = spermatheca. Scale bars: A, C = 2 mm; B = 1 mm.

Fig.42. Platevindexapplanatus(Simroth,1920) comb.nov.,anteriorreproductivesystem,malecopulatory 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.

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.

Fig. 1. Intestinal loops of type I. Small black arrows show the direction of the intestinal transport. The clockwise loop is in blue. The counterclockwise loop is in yellow. The transitional loop (between clockwise and counterclockwise loops) is in green. Red arrows indicate the orientation of the transitional loop. A. Type I (as defined by Plate 1893), with a transitional loop oriented at 3 o’clock, redrawn from Plate (1893: pl. 8, fig. 29). B. Type I, with a transitional loop oriented at 3 o’clock, Platevindex luteus (Semper, 1880) [5613] (ITBZC IM 00016), Vietnam. C. Type I, with a transitional loop oriented at 1 o’clock,P. applanatus (Simroth, 1920) [5420] (MNHN IM-2013-13765), Papua New Guinea.D. Type I, with a transitional loop oriented at 6 o’clock, P. luteus [2837] (UMIZ 00089), Ambon, Indonesia. Scale bars: B–C = 2 mm; D = 3 mm.

Fig. 10. Geographic distributions of species of Platevindex. Colored areas correspond to hypothetical ranges proposed based on all known records, and the colors are the same as those used for each species in the phylogenetic trees (Figs 1–5). Distinct colors are used for each subspecies and mitochondrial unit in P. coriaceus (Semper, 1880) as well as for each subspecies of P. burnupi (Collinge, 1902). Black dots show sites sampled for this study and red dots (China and Japan) show localities of previously published genetic sequences included in the phylogenetic analyses. A. Platevindex luteus (Semper, 1880), P. applanatus (Simroth, 1920), P. burnupi. B. Platevindex tigrinus (Stoliczka, 1869), P. coriaceus coriaceus (units #1, #2, and #3) and P. coriaceus darwinensis subsp. nov. C. Platevindex martensi (Plate, 1893), P. aptei Goulding & Dayrat sp. nov., P. amboinae (Plate, 1893) and P. latus (Plate, 1893).