Petersenaspis pakbaraensis, Plathong & Plathong & Salazar-Vallejo, 2021

Plathong, Jintana, Plathong, Sakanan & Salazar-Vallejo, Sergio I., 2021, Three new species of Sternaspidae (Annelida: Sedentaria) from Thailand, Zootaxa 5081 (3), pp. 373-388 : 382-385

Petersenaspis pakbaraensis sp. nov.

LSID urn:lsid:zoobank.org:act:3930540A-9BFA-483F-A008-54BB11DDDDFE

Figs 6 – 7

Material examined. 28 specimens, all collected from Pak Bara , Mu Ko Phetra National Park, in the Andaman Sea, Satun Province, Thailand; muddy sediments mixed with sand; coll. Marine Ecosearch Management Company ( MEM) Holotype: PSUZC-POL-0296 (1 spec.), PAK-C3-B1 (6°51’6.6”N, 99°43’36.8”E), 16 Nov 2019, 1.5 m . Paratypes: PAK-S2 (6°51’9.3”N, 99°43’33.7”E), 4 Jul 2019; PSUZC-POL-0297 (3 specs., 1 spec. on SEM stub), PAK-S2-B1; PSUZC-POL-0298 (2 specs.); PAK-S3 (6°51’7.5”N, 99°43’33.2”E), 4 Jul 2019; PSUZC-POL-0299 (3 specs.), PAK-S3-B1; PSUZC-POL-0300 (3 specs., 1 spec. on SEM stub), PAK-S3-B3; PSUZC-POL-0301 (1 spec.), PAK-S1-B1 (6°51’10.8”N, 99°43’34”E), 16 Nov 2019; PAK-C1 (6°51’9.3”N, 99°43’38.3”E), 16 Nov 2019; PSUZC-POL-0302 (4 specs., 2 specs. on SEM stubs), PAK-C1-B1; PSUZC-POL-0303 (2 specs.), PAK-C1-B2; PSUZC-POL-0304 (2 specs.), PAK-C2-B1 (6°51’7.9”N, 99°43’37.9”E), 16 Nov 2019; PSUZC-POL-0305 (2 spec., 1 spec. on SEM stub), PAK-C3-B2 (6°51’6.6”N, 99°43’36.8”E), 16 Nov 2019; PSUZC-POL-0306 (2 specs.), PAK- S6 (6°51’8”N, 99°43’3”E), 16 Feb 2018; PSUZC-POL-0307 (1 spec.), PAK-S7-B1 (6°51’14”N, 99°43’25”E), 17 Feb 2018; PSUZC-POL-0308 (1 spec.), PAK-S7-B2 (6°51’14”N, 99°43’25”E), 17 Feb 2018; AM W.52924 (1 spec.), PAK-S2 (6°51’9.1”N, 99°43’36.7”E), 4 Jul 2019 .

Description. Holotype complete with sediment particles; body papillose, 7.0 mm long, 2.9 mm wide, abdomen 4.6 mm long ( Fig. 6A ), grayish to whitish in alcohol; body wall thin, transparent ( Fig. 6A, B ). Paratypes: eight specimens complete with exposed anterior region, 3.7–8.0 mm long, 2.2–2.6 mm wide, and abdomen 4.3–5.2 mm long; 13 specimens with introvert invaginated; body 3.3–6.2 mm long, 1.9–4.4 mm wide. Live specimens showed movement by extending and retracing the anterior part of the body (the prostomium and chaetiger 1–7) to the posterior part or abdomen. When retracted, the prostomium and first three chaetigers were not exposed.

Prostomium rounded, rugose; peristomium surrounds prostomium, including mouth. Mouth circular with small papillae, extending from base of prostomium to anterior edge of first chaetiger ( Fig. 7A, D ).

First three chaetigers with 8–13 large golden spatulate hooks, and 5–6 smaller thin golden spatulate hooks, without subdistal dark areas; hook numbers similar along chaetigers 1–3. Genital papillae, small, short, thin digitiform, protrude ventrally from body wall between segments 7 and 8.

Pre-shield region with 8 segments, single lateral bundles of 2–3 capillary chaetae protruding from body wall along segments 8–15 ( Figs 6A–C , 7A–C, F ). Paratypes with capillaries along chaetigers 8 – 13. Dorsal and ventral body papillae are small, minute, lateral body papillae long and thin.

Ventro-caudal shield heart- or kidney-shaped, dark red to dark purplish, almost black. Surface with abundant long papillae, integument with ciliary clumps and suture extended throughout shield ( Figs 6A, B, F–I , 7A ). Ribs distinct, concentric lines indistinct. Anterior margins angular, anterior depression shallow. Anterior keels not exposed. Lateral margins strongly curved, lobate, expanded anteriorly, reduced posteriorly. Fan with median notch and two lateral notches, posterior notch longer, median notch deep ( Fig. 5F, H, I ).

Marginal shield chaetal fascicles include 9 lateral fascicles with chaetae, fascicles in oval arrangement, and 12 posterior fascicles, 7 at the posterior and 5 laterals (posterior chaetae mostly in bundles of three).

Branchiae abundant, emerging from a pair of branchial plates, with abundant sediment particles ( Figs 6B, D–F , 7B, C, H ). Branchial filaments include two types: coiled, whitish filaments and long straight, golden or brownish filaments, filament tips stout and smooth ( Figs 6A, B, E, F , 7B, C, H ). These two parts are connected by a small ring at the end of the branchial body (whitish) and the base of the filament (brownish); the ring can only be observed by SEM.

Variation. The ventro-caudal shield varies in large and small specimens. In larger specimens, shields are darker purple and the lateral margin of the posterior shield is expanded. In smaller specimens, shields are dark red and the lateral margin of the posterior shield is either not expanded or only slightly expanded. Ciliary clumps and papillae on the shield surface are long and more abundant in larger specimens. Genital papillae are short in paratypes and additional specimens; they are long only in the holotype, which suggests that they are retractable.

Etymology. This species named is after Pak Bara, the locality where the specimens were collected.

Habitat. The intertidal zone at Pak Bara, Mu Ko Phetra National Park, Southern of Thailand.

Distribution. Only known from the type locality, Pak Bara, Andaman Coast, Southern Thailand ( Figs 1 , 2 ).

Remarks. Petersenaspis pakbaraensis sp. nov. Resembles P. palpallatoci Sendall & Salazar-Vallejo, 2013 and P. apinyae sp. nov., in having homogenously pigmented shields, and the presence of both a median notch and two lateral notches. However, P. pakbaraensis sp. nov. differs from P. palpallatoci in having a dark purple, almost black, shield with a fan about half as wide as the anterior shield margins whereas P. palpallatoci has a reddish shield with a fan about as wide as the anterior margins ( Sendall & Salazar-Vallejo 2013).

Petersenaspis pakbaraensis sp. nov. differs from P. apinyae sp. nov. in having sediment particles on the body surface and branchial plates. Also, the papillae on the shield surface are longer and more abundant, and the integument has ciliary clumps. In P. apinyae sp. nov., the body surface and branchial plates are without sediment particles, the papillae on the shield surface are short and the integument is without ciliary clumps. Moreover, the shield of P. pakbaraensis sp. nov. is dark red to purple, the posterior shield longer and the lateral posterior shield more expanded than in P. apinyae sp. nov., which has a deeper reddish shield, the posterior shield margins are wider than they are long and the lateral posterior shield is not expanded.

Figures

FIGURE 1. Type localities of the accepted species of Petersenaspis Sendall & Salazar-Vallejo, 2013.

FIGURE 2. Sampling sites in the Gulf of Thailand and Andaman Sea where specimens of P. apinyae sp. nov. (triangles), P. narisarae sp. nov. (stars), and P. pakbaraensis sp. nov. (circles) were collected.

FIGURE 5. Petersenaspis narisarae sp. nov. Light photographs (A–B, H. Holotype, PSUZC-POL-0291; C, G. PSUZC-POL- 0292; D. PSUZC-POL-0295; E, F. AM W.52925). A. Complete specimen, dorsal view; B. Same, lateral view; C. Complete specimens with introvert invaginated, dorsal view; D. Golden hooks inside the body wall, lateral view; E. Branchial filaments, ventral view; F. Branchial plate after removal of branchiae and longer interbranchial filaments, ventral view; G–H. Ventro-caudal shield, dorsal view. Abbreviations: inner shield 1, medial shield 2, outer shield 3, interbranchial filaments ibf, branchiae br, genital papilla gp, straight filament hd, suture st.

FIGURE 6. Petersenaspis pakbaraensis sp. nov. Light photographs (A, C. Holotype PSUZC-POL-0296; B. PSUZC-POL- 0297; D. PSUZC-POL-0301; E–F. PSUZC-POL-0299; G. PSUZC-POL-0303; H. PSUZC-POL-0298; I. PSUZC-POL-0305). A. Complete specimen, dorsal view; B. Complete specimens with introvert invaginated, dorsal and lateral view; C. Genital papillae, dorsal view; D. Branchial plate after removal of branchial and interbranchial filaments, ventral view; E. Branchiae, arrow points to the connection area between branchia and filament, ventral view; F. Branchial region and ventro-caudal shield, arrow points to the connection area between branchia and filament, dorsal view; G–I. Ventro-caudal shields, dorsal view. Abbreviations: branchiae br, genital papilla gp, sand particles sp, straight filament hd, suture st.

FIGURE 7. Petersenaspis pakbaraensis sp. nov. (A, E–G. PSUZC-POL-0297; B, I. PSUZC-POL-0299; C, H. PSUZC-POL- 0305; D, G. PSUZC-POL-0302). A. Complete specimen, ventral view; B. Another complete specimen, introvert invaginated, ventral view; C. Same, lateral view; D. Anterior end, frontal view; E. Spatulate neurohooks of chaetiger 1, frontal view; F. Genital papillae, frontal view; G. Ventro-caudal shield, frontal view; H. Branchial region, tip of posterior filament in circle, ventral view; I. Tip of straight filament associated with branchia, lateral view. Abbreviations: branchiae br, capillary chaeta cc, genital papilla gp, straight filament hd, mouth mo, papilla pa, peristomium pe, prostomium pr.