Paromoionchis penangensis Dayrat & Goulding, 2019

Dayrat, Benoît, Goulding, Tricia C., Khalil, Munawar, Apte, Deepak, Bourke, Adam J., Comendador, Joseph & Tan, Shau Hwai, 2019, A new genus and three new species of mangrove slugs from the Indo-West Pacific (Mollusca: Gastropoda: Euthyneura: Onchidiidae), European Journal of Taxonomy 500, pp. 1-77 : 59-64

Paromoionchis penangensis Dayrat & Goulding gen. et sp. nov. urn:lsid:zoobank.org:act:840ABD3E-61AC-4B1E-9D83-B15A8099F0BA Figs 41–44

Etymology

Paromoionchis penangensis gen. et sp. nov. is named after Penang Island, Malaysia, in the Strait of Malacca, which is the type locality.

Material examined

Holotype

MALAYSIA • holotype (26/14 [6037] mm); Peninsular Malaysia, Penang, Pantai Acheh ; 05°24.922´N, 100°11.571´E; 1 Aug. 2016; station 261; Avicennia mangrove, with both very soft mud and hard mud; USMMC 00059.

Other material

INDIA – Andaman Islands • 1 spec. (18/10 [1086] mm); Middle Andaman, Rangat, Yerrata , Saban ; 12°27.451´N, 092°53.792´E; 10 Jan. 2011; station 56; open, impacted mangrove patch by a creek, near village, with medium trees and old logs; BNHS 92 • 2 spec. (18/8 [1100] and 9/6 [1101] mm); Middle Andaman, Rangat, Shyamkund ; 12°28.953´N, 092°50.638´E; 11 Jan. 2011; station 57; by a large river, deep mangrove with tall trees, small creeks and plenty of old logs, next to a road and a small cemented bridge over a creek; BNHS 53 • 2 spec. (20/10 [1117] and 22/12 [1118] mm); Middle Andaman, Shantipur, Kadamtala ; 12°19.843´N, 092°46.377´E; 12 Jan. 2011; station 58; open area with hard mud and many old logs, next to a mangrove with medium trees; BNHS 11 • 2 spec. (30/15 [1129] and 12/7 [1130] mm); South Andaman, Bamboo Flat, Shoal Bay ; 11°47.531´N, 092°42.577´E; 13 Jan. 2011; station 59; open mangrove with medium trees, hard mud, dead logs, next to a road and a small cemented bridge for creek; BNHS 4 . – Maharashtra • 1 spec. (35/20 [1167] mm); Watad ; 17°15.791´N, 73°17.623´E; 23 Dec. 2011; station 46; Avicennia mangrove, by field, with deep and very watery mud; BNHS 46 • 3 spec. (30/18 [1177], 20/14 [1175] and 15/10 [1173] mm); same data as for preceding; BNHS 98 • 2 spec. (16/11 [1176] and 27/21 [1182] mm); Aare Ware ; 17°04.404´N, 73°17.747´E; 24 Dec. 2011; station 47; mangrove with soft mud and some areas with pools, mostly Avicennia with a few small Rhizophora ; BNHS 42 .

MALAYSIA – Peninsular Malaysia • 2 spec. (30/20 [5990] and 30/20 [5991] mm); Kuala Gula ; 04°55.991´N, 100°26.917´E; 29 Jul. 2016; station 259; mostly Avicennia , a few Bruguiera and Rhizophora , along a creek, both soft and hard mud; USMMC 0 0 0 60 • 2 spec. (20/14 [957] and 15/10 [958] mm); Nibong Tebal, Pulau Burung ; 05°12.488´N, 100°25.564´E; 11 Jul. 2011; station 17; soft mud, open mangrove of Rhizophora , with a few Sonneratia ; USMMC 0 0 0 61 • 1 spec. (48/35 [6020] mm); Nibong Tebal, Pulau Burung ; 05°12.488´N, 100°25.564´E; 30 Jul. 2016; station 260; soft mud, open mangrove of Rhizophora , with a few Sonneratia ; USMMC 0 0 0 62 • 3 spec. (25/12 [6031], 25/18 [6033] and 25/16 [6039] mm); same data as for holotype; USMMC 0 0 0 63 .

Color and morphology of live animals ( Fig. 41 )

Live animals are most often covered with mud, in which case their dorsal color can hardly be seen. The background of the dorsal notum is brown, occasionally mottled with darker or lighter areas. In addition, in some animals, the tip of dorsal papillae (with and without dorsal eyes) can be yellow. The foot is gray, occasionally with a light yellow hue. The hyponotum is uniform gray or gray (inner ring) and yellow (outer ring). The color of both the foot and the hyponotum of an individual can change rapidly, especially when disturbed. The ocular tentacles are brown and may or may not be speckled with white dots, like the head. The ocular tentacles are short (just a few mm long).

Digestive system ( Figs 42A , 43 )

Radulae measure up to 3.2 mm in length. Examples of radular formulae are presented in Table 4. Reproductive system ( Fig. 42 B–C)

In the posterior (female) organs, the distal portion of the oviduct and of the duct to the spermatheca is wider than in other species, which makes sense given the wide penis. The male anterior organs consist of the penial complex (penis, penial sheath, vestibule, deferent duct, retractor muscle). An accessory penial gland is absent. The penial sheath is large (at least ten times as large as the deferent duct). The retractor muscle is strong, long and inserts near the heart. The deferent duct is convoluted, with many loops. Inside the penial sheath, the penis is a large (wider than long), smooth (no hooks), muscular mass.

Distinctive diagnostic features

Externally, Paromoionchis penangensis gen. et sp. nov. cannot be reliably distinguished from other species of Paromoionchis gen. nov. Its distribution only overlaps with that of P. tumidus . Our data suggest that the tips of the dorsal papillae of P. penangensis gen. et sp. nov. tend to be paler yellow, while they tend to be brighter yellow in P. tumidus . However, the internal anatomy of P. penangensis gen. et sp. nov., especially the large penis inside the large penial sheath, is very distinct from that of all other species and reliably distinguishes it from P. tumidus .

Distribution ( Fig. 6 )

Malaysia: Peninsular Malaysia, Strait of Malacca (type locality). India: Andaman Islands (Bay of Bengal), Maharashtra (W coast of India).

Habitat ( Fig. 44 )

Paromoionchis penangensis gen. et sp. nov. is found on soft and hard mud, in mangroves or in open areas near mangroves. This species was only found at three stations in the Strait of Malacca, three stations in the Andaman Islands (Bay of Bengal), and three stations in Maharashtra (W coast of India). However, at each station it was found to be quite abundant.

Figures

Fig. 41. Paromoionchis penangensis gen. et sp. nov., live animals. A. Dorsal view, 29 mm long [5990], Malaysia, Matang (USMMC 00060). B. Dorsal view, 26 mm long [6039], Malaysia, Penang (USMMC 00063). C. Holotype, dorsal view, 25 mm long [6037], Malaysia, Penang (USMMC 00059). D. Dorsal view, 22 mm long [6031], Malaysia, Penang (USMMC 00063). E. Dorsal view, 37 mm long [1167], India, Maharashtra (BNHS 46). F. Dorsal view, 30 mm long [1129], India, Andaman Islands (BNHS 4). G. Ventral view, same as D. H. Ventral view, same as A. I. Ventral view, 27 mm long [1182], India, Maharashtra (BNHS 42).

Fig. 42. Paromoionchis penangensis gen. et sp. nov., holotype, Malaysia, Penang [6037] (USMMC 00059). A. Digestive system. B. Posterior hermaphroditic (female) reproductive system. C. Male copulatory organs. 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 digestive gland; ps = penial sheath (penis inside indicated by dotted line); r = rectum; rm = retractor muscle; rs = receptaculum seminis; sp = spermatheca; st = stomach. Scales: A = 2 mm; B–C = 1 mm.

Fig. 43. Paromoionchis penangensis gen. et sp. nov., radula. A–D. Holotype, Malaysia, Penang [6037] (USMMC 00059). A. Entire radula. B. Rachidian and innermost lateral teeth. C. Lateral teeth with rachidian teeth. D. Lateral teeth. E–F. Western Peninsular Malaysia [6020] (USMMC 00062). E. Lateral teeth with rachidian teeth. F. Outermost lateral teeth. Scales: A = 0.5 mm; B, F = 20 μm; C–E = 30 μm.

Fig. 44. Paromoionchis penangensis gen. et sp. nov., habitats. A. Malaysia, Penang, open Avicennia mangrove with different types of mud (station 261, type locality). B. Western Peninsular Malaysia, Rhizophora and Sonneratia mangrove with soft mud, next to a landfill (station 17). C. India, Maharashtra, Avicennia mangrove with soft mud and a wall of large rocks (station 45). D. India, Maharashtra, Avicennia mangrove with a few small Rhizophora, soft mud and pools (station 47).

Fig. 6. Geographic distribution of the five species of Paromoionchis gen. nov. Distinct colors are used for each mitochondrial unit found in P. tumidus (Semper, 1880) comb. nov., P. boholensis gen. et sp. nov. and P. goslineri gen. et sp. nov., and the colors used for each unit are the same as those used in Figs 1–5. Colored areas correspond to hypothetical ranges proposed based on known records (all of which are new here except for the type localities of P. tumidus and P. daemelii (Semper, 1880) comb. nov.).