Petersenaspis apinyae Plathong & Plathong & Salazar-Vallejo 2021, sp. nov.

Petersenaspis apinyae sp. nov.

LSID urn:lsid:zoobank.org:act: 5083A547-AD34-4A1E-8328-1B49765744F8

Figs 3–4

Material examined. 43 specimens, all collected from 50–80 m deep in the offshore Petroleum Production Area, the Gulf of Thailand, Western Pacific; mud mixed with sand and shells; coll. Marine Ecosearch Management Company (MEM). Holotype: PSUZC-POL-0268 (1 spec.), GT-W ( 8°37’16”N, 101°46’27”E), 23 Mar 2010, 72 m. Paratypes: PSUZC-POL-0269 (1 spec.), GT-SB (9°42’35”N, 101°19’09”E), 8 Mar 2009, 60 m; PSUZC-POL-0270 (1 spec.), GT-PL (9°40’43”N, 101°23’09”E), 11 Mar 2009, 60 m; PSUZC-POL-0271 (1 spec.), GT-H (9°38’23”N, 101°13’21”E), 14 Mar 2009, 60 m; PSUZC-POL-0272 (1 spec.), GT-MK (8°33’48”N, 101°47’22”E), 20 Mar 2009, 80 m; PSUZC-POL-0273 (1 spec. on SEM stub), GT-U (8°23’02”N, 101°43’39”E), 21 Mar 2009, 80 m; PSUZC- POL-0274 (1 spec.), GT-R (8°53’01”N, 101°31’56”E), 20 Mar 2010, 70 m; PSUZC-POL-0275 (1 spec.), GT-T2-2 (8°54’16”N, 101°28’52”E), 26 Apr 2011, 72 m; PSUZC-POL-0276 (1 spec.), GT-T2-1 (8°54’06”N, 101°29’01”E), 27 Apr 2011, 72 m; PSUZC-POL-0277 (1 spec.), GT-T3 (8°33’52”N, 101°37’02”E), 28 Apr 2011, 72 m; PSUZC- POL-0278 (2 specs., 1 juvenile), GT-UP (8°37’16”N, 101°46’27”E), 1 Apr 2012, 76 m; PSUZC-POL-0279 (1 spec.), GT-L (9°06’15”N, 101°14’05”E), 10 Jun 2015, 50 m; PSUZC-POL-0280 (1 spec.), GT-SG (9°23’13”N, 101°21’35”E), 12 Jun 2015, 50 m; PSUZC-POL-0281 (1 spec.), GT-SF (9°25’09”N, 101°19’18”E), 11 Jun 2015, 50 m; PSUZC-POL-0282 (1 spec.), GT-SA (9°17’37”N, 101°25’27”E), 12 Jun 2015, 50 m; PSUZC-POL-0283 (1 spec., on SEM stub), GT-L-7 (9°06’43”N, 101°07’40”E), 9 Sep 2015, 64 m; PSUZC-POL-0284 (1 spec.), GT-W2-19 (8°29’48”N, 101°42’46”E), 9 Sep 2015, 71 m; PSUZC-POL-0285 (1 spec.), GT-W2-3 (8°29’39”N, 101°42’55”E), 9 Sep 2015, 71 m; PSUZC-POL-0286 (1 spec.), GT-W2-11 (8°30’02”N, 101°42’32”E) 10 Sep 2015, 71 m; PSUZC- POL-0287 (1 spec.), GT-R (8°53’04”N, 101°31’59”E), 25 Jun 2016, 69 m; PSUZC-POL-0288 (1 spec., on SEM stub), GT-SF (9°25’18”N, 101°19’09”E), 22 Jun 2018, 69 m; PSUZC-POL-0289 (1 spec., juvenile), GT-PG-23 (9°43’17”N, 101°22’26”E), 3 Jul 2018, 60 m; PSUZC-POL-0290 (1 spec.), GT-PG-44 (9°42’48”N, 101°22’43”E), 5 Jul 2018, 60 m; AM W.52923 (1 spec.), G4/43 REF (10°33’26”N, 100°48’03”E), 15 Apr 2011, 60 m.

Additional material: The offshore Petroleum Production Area, the Gulf of Thailand: 2 specs., GT-T2-3 (8°54’06”N, 101°29’01”E), 23 Apr 2011, 60 m; 1 spec., GT-UB (8°28’24”N, 101°52’42”E), 30 Mar 2012, 76 m; 2 specs., GT-W (8°29’50”N, 101°42’43”E), 30 Mar 2014, 71.0 m; 2 specs., GT-UB (8°28’24”N, 101°52’42”E), 9 Sep 2015, 70 m; 1 spec., GT-I (9°38’54”N, 101°12’55”E), 11 Sep 2015, 68 m; 1 spec., GT-PM-23 (9°45’28”N, 101°17’59”E), 3 Jul 2018, 73 m; 1 spec., GT-R (8°53’02”N, 101°31’56”E), 28 Mar 2019, 70 m; 4 specs., GT-Q, 30 Mar 2019,70 m; 1 spec., GT-Q-38 (8°55’59”N, 101°35’26”E); 1 spec., GT-Q-50 (8°56’00”N, 101°35’17”E); 1 spec., GT-Q-6 (8°56’09”N, 101°35’19”E); 1 spec., GT-Q-8 (8°56’10”N, 101°35’13”E).

Type locality. Gulf of Thailand, offshore petroleum concession area (Fig. 2).

Description. Holotype complete without sediment particles; body 9.2 mm long, 3.7 mm wide, abdomen 7.0 mm long, about 20 segments, whitish in alcohol (Fig. 3A–B). Abdominal papillae thin, long. Paratypes, 13 specimens complete with exposed anterior region: 11 specimens mature, body 4.0– 12.6 mm long, 1.8–3.5 mm wide, abdomen 2.7–4.2 mm long, about 20 segments: 2 specimens juvenile, body 2.0– 2.3 mm long, 0.8 mm wide, abdomen 1.5–1.6 mm long. Eight specimens with introvert invaginated; body 5.4–8.3 mm long, 2.7–4.2 mm wide, and abdomen 5.2–6.7 mm long.

Prostomium rounded (not completely exposed in holotype but fully exposed in some paratypes); peristomium rounded, with short papillae extended behind prostomium. Mouth circular with papillae extending from base of prostomium to anterior edge of first chaetiger (Figs 3C, 4A–B).

First three chaetigers with 11–16 large golden spatulate hooks and small golden spatulate hooks with up to 11 hooks, without subdistal dark areas (Figs 3A–C, 4A–D). Genital papillae short, conical, protrude ventrally from body wall between segments 7 and 8 (Figs 3A–B, 4A–D).

Pre-shield region of eight segments (Fig. 3A–B), with single lateral bundles of 2–4 (mostly 3) short thin capillary chaetae (Fig. 4E) protruding from body wall along segments 8–14. Paratype with capillaries along chaetigers 8–15. Body papillae along dorsal and ventral surfaces small, minute; lateral papillae long, thin (Fig. 4F–G).

Ventro-caudal shield with sediment particles and abundant, fine, long papillae; shield wider than long, butterfly wing-shaped, orange to reddish, integument without ciliary clumps; suture extended throughout shield. Shield without well-developed ribs and concentric lines. Anterior margins angular, anterior depression shallow. Anterior keels exposed. Lateral margins strongly curved, expanded anteriorly, reduced medially to posterior. Posterior shield wide and slightly curved. Fan with a median notch and two lateral notches. Median notch shallow (Figs 3A, E–J, 4D, G–H). Juvenile ventro-caudal shield yellowish with anterior and lateral margins rounded, fan with a median notch and smooth margin. Peg chaetae absent.

Chaetal fascicles on marginal shield include 10 lateral fascicles, chaetae of each fascicle in offset and parallel arrangement, no concentric lines, and 12 posterior fascicles, 7 with 3–4 chaetae each (1–2 fine capillary chaetae) and 5 in lateral notch with about 3 delicate and very long capillary chaetae. The long fine chaetae are located at both sides of the lateral notch, near lateral chaetae, longer than abdomen region, or about 3 times as long as posterior chaetae. These chaetae are fragile, some broken in every specimen, about 3–5 intact chaetae instead of 15.

Branchial filaments abundant (Figs 3A–B, E, 4F, H), consisting of two parts; the first part is the branchial body, coiled, the second a long filament with bloated posterior (Figs 3A–B, 4H, F, I), the base of branchial body connected to branchial plate. Branchial plates with long papillae and sediment particles (Fig. 3D). The anterior branchial body can retract leaving the long filament exposed. The branchia and filament are connected by a small ring (Fig. 4K). Branchiae are whitish, neither smooth nor covered with cilia (Fig. 4L), and the filament holder is golden or brownish, smoother than the branchia and composed of small rings (Fig. 4M), the posterior end is bloated with larger rings. The outer surface of each posterior ring is embossed with a row of ovoid shapes and tips roughly resembling the pads of a gecko’s feet. Their tips are often swollen and have a tapered end (Fig. 4J). They might possibly help by sucking or sticking to adjacent sediment particles to support the body.

Variation. Juveniles with body wall and ventro-caudal shield very thin, transparent; shield light yellow to light brown. Adults with thicker body wall and harder shields.

Etymology. The species name is in recognition of Mrs. Apinya Sukolra of the SEM section, Office of Scientific Instrument and Testing (OSIT), Prince of Songkla University, for her assistance with SEM photographs of polychaetes during the last 4 years.

Habitat. Found at 50–80 m depth, in muddy sediments mixed with sand and shells, offshore Gulf of Thailand.

Distribution. Only known in the offshore Petroleum Production Area, Gulf of Thailand (Figs 1, 2).

Remarks. Petersenaspis apinyae sp. nov. resembles P. palpallatoci Sendall & Salazar-Vallejo, 2013, P. narisarae sp. nov., and P. pakbaraensis sp. nov. in having homogenously pigmented shields and both a median notch and two lateral notches. However, P. apinyae sp. nov. has more introvert hooks and posterior chaetae than P. palpallatoci with 20–22 introvert hooks per fascicle and 12 fascicles of posterior shield chaetae. P. palpallatoci has about 12–14 introvert hooks and 10 fascicles of posterior shield chaetae (Sendall & Salazar-Vallejo 2013). Moreover, P. apinyae sp. nov. has a butterfly wing-shaped shield with lateral margins strongly curved and expanding anteriorly; and more lateral abdomen chaetae than P. palpallatoci, with up to 3 simple chaetae per bundle from segment 8–15. In P. palpallatoci, lateral shield margins are rounded, and there are only 2 simple lateral abdominal chaetae per bundle from segment 9–10 (Sendall & Salazar-Vallejo 2013).

Petersenaspis apinyae sp. nov. differs from P. pakbaraensis sp. nov. by having 20–22 spatulate hooks per fascicle whereas P. pakbaraensis sp. nov. has 13–19. P. apinyae sp. nov., unlike P. pakbaraensis sp. nov., does not have ciliary clumps, and the median notch is narrower and shallower than in P. pakbaraensis. The posterior shield is wide and slightly curved, whereas the posterior shield of P. pakbaraensis sp. nov. is narrow, protruding and strongly curved.

Petersenaspis apinyae sp. nov. differs from P. narisarae sp. nov. by having a homogenously pigmented shield whereas P. narisarae has colored bands on its shield. Also, the abdomen of P. apinyae sp. nov. is not expanded.