Sternaspis spinosa Sluiter, 1882

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 : 409-411

Sternaspis spinosa Sluiter, 1882

Figures 1 , 5 , 6

Sternaspis spinosa: Sluiter, 1882: 277 , Pl. 1, fig. 1. Sendall & Salazar-Vallejo, 2013: 47 –50, fig. 14.

Material examined. South China Sea. MBM 020947 (1 spec.), R/V 101, Sta. 6181, 18°12’N, 109°45’E, 68 m, sandy mud, coll. Jixing Liu, 12 May 1960 . Body 28.2 mm long, 11.7 mm wide; abdomen 16.4 mm long; left shield plate 4.6 mm long, 5.4 mm wide. MBM 020948 (1 spec.), R/V 220, Sta. 6044, 18°12’N, 109°45’E, 43.6 m, soft mud, coll. Jingzuo Qu, 9 Apr. 1960 . Body 29.6 mm long, 9.1 mm wide; abdomen 16.5 mm long; left shield plate 3.4 mm long, 3.9 mm wide. MBM 020931 (1 spec.), R/ V Hanggong I, Sta. 6116, 21°00’N, 111°30’E, 44 m, soft mud, coll. Zhican Tang, 22 Feb. 1959 . MBM 020933 (1 spec.), R/V Hanggong I, Sta. 6062, 21°45’N, 113°30’E, 35 m, fine sand and mud, coll. Fuzeng Sun. 24 Apr. 1959. MBM 020965 (1 spec.), R/V 121, Sta. 6138, 20°30’N, 110°00’E, 31 m, sandy mud, coll. Zhican Tang, 29 Oct. 1959. MBM 020925 (1 spec.), R/V Hanggong, Sta. 6064, 21°15’N, 114°00’E, 52 m, sand, coll. Fengshan Xu, 18 Oct. 1959. MBM 020961 (1 spec.), SCS, R/V 171, Sta. 6138, 20°30’N, 111°00’E, 30 m, fine sand and soft mud, coll. Xiutong Ma, 26 Apr. 1959. MBM 020932 (1 spec.), SCS, R/V Hanggong I, Sta. 6062, 21°45’N, 113°30’E, 32 m, soft mud, coll. Jingzuo Qu, 16 Feb. 1960. MBM 020964 (2 spec.), SCS, 121, Sta. 6115, 21°15’N, 111°30’E, 28 m, sandy mud, coll. Zhican Tang, 17 Oct. 1959. MBM 020944 (1 spec.), SCS, R/V 101, Sta. 6135, 19°15’N, 111°15’E, 17 m, soft mud, coll. Jixing Liu, 10 Apr. 1960. MBM 020954 (7 spec.), SCS, R/V 220, Sta. 6034, 22°15’N, 115°00’E, 42 m, sand and soft mud, coll. Jingzuo Qu, 13 Jul. 1959. MBM 020928 (6 spec.), SCS, R/V Hanggong, Sta. 6061, 22°00’N, 113°30’E, soft mud, coll. Jingzuo Qu, 13 Jul. 1959. Two anterior ends retracted. Body 22.2–30.2 mm long, 8.4–13.4 mm wide; abdomen 12.2–20.9 mm long; left shield plate 3.1–4.6 mm long, 3.2–5.4 mm wide. MBM 020926 (23 spec. including 13 juv.), R/V Hanggong, Sta. 6061, 22°00’N, 113°30’E, 7 m, soft mud, coll. Yongliang Wang, 18 Oct. 1959. Three juveniles are imaged in Figure 6 . MBM 020927 (1 spec.), R/ V Hanggong, Sta. 6089, 21°15’N, 112°30’E, 41 m, muddy sand, coll. Zhican Tang, 7 Apr. 1960 . MBM 020974 (1 spec.), R/V 220, Sta. 6034, 22°15’N, 115°00’E, 42 m, sandy mud, coll. Weiquan Zhang, Song, 11 Dec. 1959. MBM 020963 (1 spec.), R/V 228, Sta. 6181, 18°12’N, 109°45’E, 68 m, sandy mud, coll. Zhican Tang, 23 Nov. 1959. MBM 020959 (1 spec.), R/V 171, Sta. 6117, 20°45’N, 111°30’E, 48.5 m, sand and soft mud, coll. Yongliang Wang, 12 Apr. 1959. MBM 020949 (3 spec.), R/V 220, Sta. 6033, 22°30’N, 115°00’E, 24.5 m, soft mud, coll. Jingzuo Qu, 9 Apr. 1960. MBM 020951 (2 spec.), R/V 220, Sta. 6019, 22°45’N, 116°00’E, 21 m, soft mud, coll. Mu Chen, Lingxin Lv, 14 Apr. 1960. MBM 021012 (2 spec.), R/V Hanggong I, Sta. 6075, 21°30’N, 113°00’E, 36 m, soft mud, coll. Xiutong Ma, 6 Jul. 1959. MBM 021007 (3 spec.), R/V 171, Sta. 6115, 21°15’N, 111°30’E, 29 m, soft mud, 24 Jan. 1959. Two anterior ends retracted. Body 43.3 mm long, 16.2–16.9 mm wide; abdomen 24.8–26.5 mm long; left shield plate 5.0– 5.6 mm long, 6.5–7.5 mm wide. MBM 020929 (2 spec.), R/ V Hanggong I, Sta. 6104, 21°15’N, 112°00’E, 34 m, soft mud, coll. Fuzeng Sun, 20 Feb. 1959 . MBM 021013 (4 spec.), R/V Hanggong I, Sta. 6061, 22°00’N, 113°30’E, 7 m, soft mud, coll. Xiutong Ma, 16 Jul. 1959, Including 2 juveniles. MBM 021245 (2 spec.), R/V S, Sta. 6044, 22°00’N, 114°30’E, 39.9 m, 9 Apr. 1959. MBM 021246 (1 spec.), R/V 101, Sta. 6228, 17°00’N, 108°30’E, 93 m, fine sand and mud, coll. Jixing Liu, 15 May 1960. MBM 021250 (1 spec.), R/V 121, Sta. 6137, 20°45’N, 111°00’E, 31 m, soft mud, coll. Zhican Tang, 30 Oct. 1959. MBM 020950 -1 (2 spec.), R/V 220, Sta. 6034, 22°15’N, 115°00’E, 41 m, soft mud, coll. Jingzuo Qu, 12 Apr. 1960. MBM 283396 (1 spec.), Xinying , Hainan Island, HBR- 3, approximate co-ordinate: 19°54’N, 109°30’E, 15 Dec. 2010 .

Description. Largest specimen 43.3 mm long, 16.9 mm wide; left shield plate 5.58 long and 7.46 wide. Body pale or yellowish, introvert with similar pigmentation as abdomen, constriction or waist segments relaxed ( Figs 5 A; 6A).

Prostomium hemispherical, projected, translucent pale ( Figs 5 B; 6D). Eyespots not seen. Boundary distinct in side and back of prostomium. Peristomium whitish, flat, barely extending laterally and ventrally to anterior margin of first chaetiger. Mouth circular, projected, wider than prostomium, covered by minute papillae ( Figs 5 B; 6D).

First three chaetigers each with 18–25 bronze hooks per side. Hooks tapering to sharp points, sub-distally darker, gradually shortened towards ventrolateral side ( Figs 5 B, C; 6D). Introvert covered by minute papillae ( Figs 5 C; 6D). Genital papillae conical, distally truncate, protruding ventro-laterally from inter-segmental groove between segments 7 and 8 ( Fig. 5 A). Anterior abdomen with 7 segments; papillae minute, evenly distributed ( Fig. 6 A), eroded in larger specimens ( Fig. 5 A). Capillaries not seen.

Ventro-caudal shield brick red, darker in central area; at least twice wider than long. Concentric lines welldefined ( Fig. 5 E–H). Anterior margins angular, anterior depression deep; anterior keels covered by translucent integument layer. Suture only visible in anterior region, fused posteriorly into a shallow furrow. Lateral margins rounded, smooth, expanded laterally, reduced posteriorly. Fan slightly ribbed, truncate, not extending beyond posterolateral corners; margin crenulated, without a median notch ( Fig. 5 E–H).

Marginal chaetae including 10 lateral fascicles and 5 posterior ones ( Fig. 5 E–H); lateral fascicles successively longer from anterior to posterior, last three bundles close together, chaetae 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, inserted in edge of peg chaetae, 2–3 times as long as posteriormost lateral fascicle.

A fascicle of shorter capillary chaetae located between peg chaetae and outermost lateral fascicle, 3 times as long as posterior chaetae.

Branchiae abundant, inserted on two plates. Branchial filaments slender, spiraled or curled; inter-branchial papillae long, curled, with fine sediment particles. Branchial plates long, widely divergent, distal portion narrow ( Figs 5 D; 6E).

Variation. The ventro-caudal shield varies in two aspects. First, the shields in most individuals are laterally expanded with rounded lateral margins ( Fig. 5 F–H), while in a few other individuals the lateral margins are straight with relatively better developed anterolateral and posterolateral corners ( Fig. 5 E). Second, the radial ribs are usually present in the fan and form a slightly crenulated posterior margin ( Fig. 5 E–G), but may also be indistinct forming a smooth margin ( Fig. 5 H).

Juvenile shield. Immature specimens illustrated in Figure 6 were collected together with the adults of S. spinosa . They have morphologically similar ventro-caudal shields and branchial plates ( Fig. 6 B, C, E), and are thus regarded as juveniles of S. spinosa . Their shields are mainly reddish-orange, with one or two annulated concentric bands near the margin. The shield width is not significantly greater than its length ( Fig. 6 B, C). The radial ribs are poorly defined especially in the smaller body ( Fig. 6 B). The suture extends throughout the shield. The marginal regions of the shield are covered by whitish filamentous papillae. As the body size increases, the radial stripes appear on the lateral plates, and the main ribs also become visible ( Fig. 6 C).

Distribution. Sternaspis spinosa is widely distributed in the tropical Western Pacific, ranging from the South China Sea (water depth 7–93 m, Fig. 1 ) southwards to the Coral Sea off Australia. It is the most common and abundant sternaspid in the northern South China Sea. According to our material examined, the distribution of this species is generally not beyond 23 degrees North.

Remarks. Sternaspis spinosa had long been a confusing species because its original description was brief and its type material was unknown until Sendall & Salazar-Vallejo (2013) designated a neotype collected from the Bay of Batavia, Java. Our specimens agree well with the neotype in general morphology. The differences include that the anterior keels are exposed and the suture is visible throughout the shield in the neotype, while in our material the anterior keels are covered by translucent integument and the suture is only visible in the anterior region and fused posteriorly. A possible reason is that the integument layer covering the shield was partly corroded in the old specimen which was collected in 1889 and designated as the neotype.

The species can be identified by a combination of characters as follows: the shield width is twice larger than its length; the concentric lines are conspicuous and the ribs are slightly developed; and the posterior margin is truncate without a median notch.

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 5. Sternaspis spinosa Sluiter, 1882. A. Complete specimen (MBM 020948) in ventral view, branchiae removed, arrows pointing to genital papillae; B, C. Anterior end (MBM 020947) in ventral and left-lateral view; D. Branchial plates (MBM 198745) in rear end view, branchiae removed; E – H. Shield morphology of four specimens (E: MBM 020948; F: MBM 020947; G: MBM 198745; H: MBM 020932). Scale bars: 5 mm (A), 0.5 mm (B) and 1 mm (C – H).

FIGURE 6. Juveniles of Sternaspis spinosa Sluiter, 1882. A. Three specimens (A 1 – A 3: MBM 020926); B. Shield morphology of specimen A 1; C. Shield morphology of specimen A 3; D. Anterior end of specimen A 3 in ventral view; E. Branchial plates of specimen A 3 in rear end view, branchiae removed. Scale bars: 2 mm (A) and 0.5 mm (B – E).