Platevindex aptei Goulding & Bourke & Comendador & Khalil & Quang & Tan & Tan & Dayrat 2021, sp. nov.

Platevindex aptei Goulding & Dayrat sp. nov.

urn:lsid:zoobank.org:act: 25DECF9A-226F-40A8-BC49-99815E6B2B9D

Figs 59–63

Platevindex aptei sp. nov. is named for Deepak Apte, a great naturalist and the Executive Director of the Bombay Natural History Society, Mumbai, India. Deepak Apte provided great help in the organization of our fieldwork in India as well as with molecular lab work at the National Centre for Cell Science in Pune. We would not have been able to explore the mangroves of India without his assistance.

Holotype

INDIA • holotype (45/20 [1112] mm); Andaman Islands, Shantipur, Kadamtala; 12°19.844′ N, 92°46.377′ E; 12 Jan. 2011; station 58, mangrove creek, open forest, lots of dead logs and trees; BNHS 3-1112.

Other material

INDIA – Andaman Islands • 1 spec. (35/20 [1092] mm); Shamkund, near Rangat; 12°29.448′ N, 92°50.620′ E; 11 Jan. 2011; station 57; ditches by road to the mangroves with high trees down to the mud on side of river; BNHS 8-1092 • 1 spec. (35/20 [1093] mm); same collection data as for preceding; BNHS 8-1093 • 3 specs (55/35 [#1], 50/35 [#2] and 25/18 [#3] mm); same collection data as for preceding; BNHS 8 • 1 spec. (25/20 [1111] mm); Shantipur, Kadamtala; 12°19.844′ N, 92°46.377′ E; 12 Jan. 2011; station 58; mangrove creek, open forest, lots of dead logs and trees; BNHS 3-1111 • 1 spec. (38/22 [1121] mm); Shoal Bay, by Bamboo Flat; 11°47.531′ N, 92°42.576′ E; 13 Jan. 2011; station 59; ditches and mud along the road; BNHS 14-1121.

MALAYSIA – Peninsular Malaysia • 1 spec. (28/17 [no DNA] mm); Penang; 05°23.782′ N, 100°11.469′ E; 8 Jul. 2011; station 12; open Avicennia mangrove with many dead logs; USMMC 00035 • 2 specs (50/39 [#1] and 35/23 [932] mm); Merbok; 05°39.035′ N, 100°25.782′ E; 14 Jul. 2011; station 21; deep Rhizophora forest with old, tall trees, hard mud, many small creeks and dead logs; USMMC 00036 • 1 spec. (31/24 [917] mm); Matang; 04°50.154′ N, 100°36.868′ E; 20 Jul. 2011; station 29; old Rhizophora mangrove with hard mud and open space between trees; USMMC 00037 • 3 specs (42/25 [5967], 37/21 [5968] and 35/22 [5955] mm); Matang; 04°50.217′ N, 100°36.826′ E; 26 Jul. 2016; station 256; old Rhizophora mangrove with hard mud and open space between trees; USMMC 00078.

Color and morphology of live animals (Fig. 59) Live animals are not usually covered with mud, and their natural color is usually visible without washing. The dorsal notum is brown, sometimes with darker markings. The notum bears low, elongated (longitudinal) ridges. The foot is black (Malaysia) or dark brown (India). The background of the hyponotum is bright yellow (Malaysia) to light yellow or beige (India) with a varying number of spots that range from light brown (India) to dark brown or black (Malaysia). Spots tend to be more concentrated around the margin of the hyponotum, but their density is highly variable (from only around the margin to the entire hyponotum). Exceptionally, the hyponotum can be homogenously dark brown with only a small yellow band around the foot. Small or juvenile specimens tend to have fewer or no spots on the hyponotum. Papillae with dorsal eyes are present. Their exact number is variable (between 35 and 50). Each papilla bears one dorsal eye. The dorsal eyes are distributed across the notum, with numerous eyes at the margin of the notum (i.e., many eyes are <2 mm from the notum edge).

Digestive system (Figs 2F, 60, 61 A–B)

Radulae measure up to 6.4 mm long. Examples of radular formulae are presented in Table 5. The intestinal loops are of type II, with a transitional loop oriented between 7 and 9 o’clock (Figs 2F, 61 A–B).

Reproductive system (Figs 61C, 62)

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 and is sharply bent (U-shaped). The deferent duct is slightly longer than the oviduct, not attached to it, and loosely to highly convoluted (Fig. 61C). The penial sheath is very thick but the penis inside is extremely thin. The vestibule is cylindrical and attached to the anterior, dorsal wall of the visceral cavity by many short muscle fibers. The distal, flexible region of the penis with hooks is approximately 2.5 to 5 mm long and is very narrow, approximately 80 µm wide. Penial hooks are large, approximately 30 to 40 µm long, and can be seen inside the semi-transparent penis. The retractor muscle of the penis inserts at the posterior end of the visceral cavity, near the rectum. The retractor muscle varies from much shorter than the penial sheath (one-fifth its length) to approximately as long as the penial sheath. In the penial complex, the deferent duct is convoluted in small loops (Fig. 62D).

Distinctive diagnostic features (Table 4)

Externally, Platevindex aptei sp. nov. can be easily distinguished from all other known species of Platevindex by its strikingly distinctive black or dark brown foot. The bright yellow or beige hyponotum distinguishes it from most other species of Platevindex, but this also occurs in P. martensi. Low, elongated (longitudinal) ridges on the dorsal notum are diagnostic of P. aptei sp. nov. as well as P. martensi. Internally, the thick penial sheath with a very narrow penis is a distinctive characteristic of P. aptei sp. nov., and the flexible region of the penis bearing spines is longer in P. aptei sp. nov. (2.5–5 mm) than in P. martensi (2–2.5 mm long).

Distribution (Fig. 10C)

India: Andaman Islands. Malaysia: Peninsular Malaysia.

Habitat (Fig. 63)

Platevindex aptei sp. nov. is found in mangroves, typically on large, dead logs, as well as on tree trunks and roots, and cement ditches adjacent to mangroves, but is not found directly on mud. It is usually found in the high intertidal. It does not live on rocky shores.

Platevindex aptei sp. nov. may also be present in Singapore, although it was not found there during our recent visit. Many onchidiid species present in the Bay of Bengal and Peninsular Malaysia are also present in Singapore, such as Platevindex coriaceus, P. tigrinus, P. martensi, Peronina tenera (Goulding et al. 2018c), Onchidium typhae (Dayrat et al. 2016), Melayonchis siongkiati and M. eloisae (Dayrat et al. 2017). However, there are other instances of onchidiid species which have not recently been found in Singapore even though they should be there based on their known geographic distribution, such as Onchidium stuxbergi (Dayrat et al. 2016) and Melayonchis aileenae Dayrat & Goulding, 2017 (Dayrat et al. 2017).A photo of a slug erroneously identified as Onchidium griseum, but which actually illustrates Platevindex aptei sp. nov., was found online, posted on the website WildSingapore.com with photos of P. martensi. The locality listed with the photo online is Sungei Buloh Wetland Reserve, Singapore, suggesting that P. aptei sp. nov. is present there. However, if P. aptei sp. nov. is present in Singapore, it may be at low abundance.