Sternaspis sunae, 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 : 413

Sternaspis sunae sp. nov.

Figure 8

Type material. South China Sea. Holotype: MBM 198787 , R/V sy3, Nansha Islands , Sta. 59, 224 m, 22 Sep. 1994 . Paratype: MBM238398 (1 spec.), same collection information as the holotype. Body partly shrinks, 30 mm long, 10.9 mm wide; abdomen 16.2 mm long; left shield plate 4.84 mm long, 5.65 mm wide.

Description. Holotype (MBM198787) complete, 38 mm long, 17 mm wide; abdomen 25 mm long; left shield plate 5.23 mm long, 6.21 mm wide. Body pale to yellowish, introvert fully exposed, with similar pigmentation as abdomen, constriction or waist segments relaxed ( Fig. 8 A).

Prostomium hemispherical, translucent pale ( Fig. 8 B). Eyespots not seen. Boundary distinct on side and back of prostomium. Peristomium projected, covered with sediment particles, barely extending laterally and ventrally to anterior margin of first chaetiger. Mouth circular, projected, wider than prostomium, covered by minute papillae ( Fig. 8 B).

First three chaetigers each with 14–17 light brown hooks per side. Hooks slightly expanded sub-distally, spearhead-like with a medial furrow; hooks gradually shortened towards ventrolateral side ( Fig. 8 B–D). Introvert covered by minute papillae. Genital papillae conical, with indistinct annular rings, protruding ventro-laterally from inter-segmental groove between segments 7 and 8. Anterior abdomen with 7 segments, partly covered by sediment; papillae minute, evenly distributed ( Fig. 8 A, E). Capillaries not seen.

Ventro-caudal shield brick red, with distinct concentric lines near margin; shield nearly rectangular, much wider than long (width-length ratio: 2.33–2.37) ( Fig. 8 G, H). Anterior margins angular, anterior depression shallow; anterior keels covered by translucent integument layer. Suture restricted to anterior region, fused posteriorly into a furrow. Lateral margins straight, smooth, expanded posteriorly. Main ribs distinct, forming a shallow groove between lateral plates and fan; fan slightly ribbed, truncate, not extending beyond posterolateral corners; margin smooth or slightly crenulated, without a distinct median notch ( Fig. 8 G, H).

Marginal chaetae golden yellow, including 10 lateral fascicles and 6 posterior ones ( Fig. 8 G, H); lateral fascicles successively longer from anterior to posterior, chaetae arranged in semi-closed oval; 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 capillary chaetae inserted between peg chaetae and outermost posterior fascicle, at least 3 times as long as posterior chaetae.

Branchiae abundant, inserted on two plates. Branchial filaments slender, spiraled or curled; inter-branchial papillae long, curled, covered with fine sediment particles. Branchial plates oval, nearly parallel, with unclear boundaries ( Fig. 8 F).

Variations. The lateral margins of the shield are nearly straight ( Fig. 8 G) or slightly expanded posteriorly ( Fig. 8 H). The branchial plates are almost parallel in the holotype ( Fig. 8 F) but divergent in the paratype.

Etymology. Sternaspis sunae is named to honor Professor Ruiping Sun, in recognition of her contribution to the polychaete taxonomy in China, and in appreciation of her mentoring to the first author during the graduate student period.

Distribution. South China Sea off the Nansha Islands (water depth 224 m).

Remarks. The introvert hooks of Sternaspis sunae sp. nov. are spearhead-like with a median longitudinal furrow in the end portion, resembling those present in the genus Petersenaspis ( Figs 2 F; 8D). However, all species of Petersenaspis have 8 segments in the pre-shield abdomen, and their shields have feebly developed ribs and no concentric lines. By contrast, S. sunae sp. nov. has seven segments in the pre-shield region and both radial ribs and concentric lines are well developed in the shield, like members of Sternaspis . These distinct features indicate the new species should be classified into the genus Sternaspis , though most species of Sternaspis have tapering introvert hooks.

Sternaspis sunae sp. nov. is most similar to the new species S. wui sp. nov. described above because they have nearly rectangular ventro-caudal shields, six posterior chaetal fascicles, and similar color and arrangement of the chaetal fascicles. The two species differ clearly in the shape of the introvert hooks, which are spearhead-like with a median longitudinal furrow in S. sunae sp. nov., but are tapering in S. wui sp. nov. ( Figs 7 D; 8D). Besides, the two species can also be distinguished by the features of the shield. Sternaspis sunae sp. nov. has the shield suture restricted only in the anterior region and the concentric lines only visible near the margin, while in S. wui sp. nov. the suture extends throughout the shield and the concentric lines are distinct from the margin to the center.

Figures

FIGURE 2. Petersenaspis salazari sp. nov., holotype (A, B, E – G: MBM 020924) and paratype (C, D: MBM 020958). A. Complete specimen in ventral view, arrows pointing to genital papillae; B. Introvert hooks and four bands of numerous dark papillae in the anterior segments; C. Branchial plates in rear end view, branchiae removed; D, E. Shield morphology; F. Introvert hooks close-up, showing the sub-distally expanded and obliquely truncate pattern, arrows pointing to the median furrows; G. Abdomen in lateral view, showing clusters of papillae arranged in rows. Scale bars: 5 mm (A), 1 mm (B – E), 0.2 mm (F) and 2 mm (G).

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).

FIGURE 8. Sternaspis sunae sp. nov., holotype (A – G: MBM 198787) and paratype (H: MBM 283398). A. Complete specimen in ventral view, branchiae removed, 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 spearhead-like pattern, arrows pointing to the median longitudinal furrows; 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).