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

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Paromoionchis penangensis Dayrat & Goulding

gen. et sp. nov.

Paromoionchis penangensis Dayrat & Goulding gen. et sp. nov. Figs 41–44 View Fig View Fig View Fig View Fig


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

Material examined


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. GoogleMaps

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 View Materials GoogleMaps 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 View Materials GoogleMaps 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 View Materials GoogleMaps 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 View Materials . GoogleMaps 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 View Materials GoogleMaps 3 spec. (30/18 [1177], 20/14 [1175] and 15/10 [1173] mm); same data as for preceding; BNHS 98 View Materials GoogleMaps 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 View Materials GoogleMaps .

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 GoogleMaps 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 GoogleMaps 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 GoogleMaps 3 spec. (25/12 [6031], 25/18 [6033] and 25/16 [6039] mm); same data as for holotype; USMMC 0 0 0 63 GoogleMaps .

Color and morphology of live animals ( Fig. 41 View Fig )

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 View Fig , 43 View Fig )

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

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

Habitat ( Fig. 44 View Fig )

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.