Sternaspis wui, Wu, Xuwen & Xu, Kuidong, 2017

Wu, Xuwen & Xu, Kuidong, 2017, Diversity of Sternaspidae (Annelida: Terebellida) in the South China Sea, with descriptions of four new species, Zootaxa 4244 (3), pp. 403-415 : 411-413

Sternaspis wui sp. nov.

Figures 1 , 7

Type material. South China Sea. Holotype: MBM 020945 , R/V 220, Sta. 6163, 17°45’N, 110°30’E, 230 m, soft mud, coll. Shoupeng Shen , 9 Mar. 1960. Paratype: MBM 021253 (1 spec.), R/V 101, Sta. 6145, 18°15’N, 111°00’E, 173 m, soft mud, coll. Jixing Liu, 8 Apr. 1960. Body 18.0 mm long, 7.6 mm wide; abdomen 11.3 mm long; left shield plate 3.10 mm long, 3.39 mm wide.

Description. Holotype (MBM 020945) complete, 25.0 mm long, 10.7 mm wide; abdomen 16.4 mm long; left ventro-caudal shield plate 3.53 mm long, 4.23 mm wide. Body whitish to pale, introvert slightly shrunk, with similar pigmentation as abdomen, constriction or waist segments relaxed ( Fig. 7 A).

Prostomium hemispherical, translucent pale ( Fig. 7 B). Eyespots not seen. Boundary distinct in side and back of prostomium. Peristomium whitish, flat, with few papillae, barely extending laterally and ventrally to anterior margin of first chaetiger. Mouth circular, projected, wider than prostomium, covered by minute papillae ( Fig. 7 B).

First three chaetigers each with 15–17 light bronze hooks per side. Hooks tapering, sub-distally darker, becoming gradually shorter towards ventrolateral side ( Fig. 7 B–D). Introvert covered by minute papillae ( Fig. 7 B, C). Genital papillae conical, distally truncate, protruding ventro-laterally from inter-segmental groove between segments 7 and 8. Anterior abdomen with 7 segments, papillae minute, evenly distributed on ventral side ( Fig. 7 A, E). Capillaries not seen.

Ventro-caudal shield brick red, nearly rectangular, much wider than long (width-length ratio: 2.19–2.40) ( Fig. 7 G, H). Concentric lines well-defined from margin to center. Anterior margins angular to slightly rounded, anterior depression shallow; anterior keels covered by translucent integument layer. Suture extends throughout shield. Lateral margins straight, smooth. Main ribs distinct, forming a boundary between lateral plates and fan; fan slightly ribbed, truncate, not extending beyond posterolateral corners; fan margin smooth, with a median notch ( Fig. 7 G, H).

Marginal chaetae golden yellow, including 10 lateral fascicles and 6 posterior ones ( Fig. 7 G, H); lateral fascicles successively longer from anterior to posterior, last two bundles close together, chaetae arranged in shallow curve; posterior fascicles similar in length, chaetae in linear arrangement. Peg chaetae tapering, with stout base. A small fascicle of very long, delicate capillary chaetae located in upper edge of peg chaetae. A fascicle of shorter capillaries inserted between peg chaetae and outermost posterior fascicle, 2–3 times as long as posterior chaetae.

Branchiae abundant ( Fig. 7 A), inserted on two plates. Branchial filaments slender, spiraled or curled; interbranchial papillae long, curled, with fine sediment particles attached. Branchial plates short, oval, slightly divergent with round distal portion ( Fig. 7 F).

Variation. The shield pigmentation is brick red ( Fig. 7 H) or yellowish-brown ( Fig. 7 G). The median notch is deep in the holotype but indistinct in the other one, and this difference is probably due to the small body size of the latter ( Fig. 7 G, H).

Etymology. Sternaspis wui is named to honor the late Professor Baoling Wu (1925–1998), a pioneer in studying the polychaete taxonomy in China.

Distribution. Continental shelf to the margin of the continental slope in the northern South China Sea (water depth 173–230 m) ( Fig. 1 ).

Remarks. Sternaspis wui sp. nov. has a nearly rectangular ventro-caudal shield which is much wider than long (width-length ratio: 2.19–2.40). The new species is similar to the following recorded species in having straight posterior shield margins: S. africana Augener, 1918 , S. monroi Salazar-Vallejo, 2014 , S. princeps Selenka, 1885 , S. rietschi Caullery, 1944 , S. spinosa Sluiter, 1882 , S. thalassemoides Otto, 1882 , and S. thorsoni Sendall & Salazar- Vallejo, 2013. However, in S. princeps , S. thalassemoides and S. thorsoni the shield width is two times less than its length, while all the other species have relatively wider shields. Sternaspis africana , S. rietschi and S. spinosa have rounded lateral margins, while both S. wui sp. nov. and S. monroi have truncate lateral margins. Sternaspis wui sp.

nov. resembles S. monroi in both the lateral and posterior margins, but the main difference lies in the development of the concentric lines, which are well defined in S. wui but not visible in S. monroi .

Sternaspis wui sp. nov. strongly resembles the new species S. sunae sp. nov. described below in terms of the shield morphology. However, the two species differ in the shape of the introvert hooks (see below).

Figures

FIGURE 1. Distribution of four sternaspid species (except Sternaspis sunae sp. nov.) in the northern South China Sea based on the examined material. Note: The specimens of S. sunae were collected from the sea area of the Nansha Islands without information of exact co-ordinates.

FIGURE 7. Sternaspis wui sp. nov., holotype (A – G: MBM 020945) and paratype (H: MBM 021253). A. Complete specimen in ventral view, arrows pointing to genital papillae; B. Anterior end in frontal view; C. Introvert hooks of anterior three chaetigers; D. Introvert hooks close-up, showing the tapering end; E. Abdomen in lateral view; F. Branchial plates in rear end view, branchiae removed; G, H. Shield morphology. Scale bars: 5 mm (A), 1 mm (B, C, F – H), 0.2 mm (D) and 2 mm (E).