Sternaspis liui, Wu, Xuwen, Salazar-Vallejo, Sergio I. & Xu, Kuidong, 2015

Wu, Xuwen, Salazar-Vallejo, Sergio I. & Xu, Kuidong, 2015, Two new species of Sternaspis Otto, 1821 (Polychaeta: Sternaspidae) from China seas, Zootaxa 4052 (3), pp. 373-382 : 379-382

Sternaspis liui sp. nov.

Figs 1 , 4 , 5

Type material. Holotype: MBM283058, YS, R/V Kexue III, Sta. 3600-4B, 35°59’N, 122°00’E, 43.3 m, mud, coll. Junlong Zhang, Ping Ning and Yang Li, 17 Nov. 2011. Paratypes: MBM283059 (20 spec.), same collecting information as holotype. 23.8–35 mm long, 8.4–12.9 mm wide; abdomen 12.8–23.6 mm long; left shield plate 3.2– 5.2 mm long, 3.1–5.1 mm wide. MBM 020934 (1 spec.), YS, R/V Handan, Sta. 3016, 36°30’N, 121°45’E, 28 m, brown mud, coll. Gongyi Hu, 23 Apr. 1959. 25.7 mm long, 8.2 mm wide; abdomen 14.8 mm long; left shield plate 3.5 mm long, 3.4 mm wide.

Additional material. MBM 020920 (1 spec.), YS, R/V Yancheng, Sta. 3047, 36°30’N, 121°00’E, 34 m, silt and gravel, coll. Mu Chen, 26 Oct. 1959. 27.1 mm long, 8.6 mm wide; abdomen 21.0 mm long; left shield plate 3.1 mm long, 3.1 mm wide. MBM 020921 (1 spec.), YS, R/V Yancheng, Sta. 3015, 36°30’N, 121°30’E, 28 m, brown mud, coll. Gongyi Hu, 12 Jul. 1959. 33.3 mm long, 10.7 mm wide; abdomen 20.3 mm long; left shield plate 4.6 mm long, 4.6 mm wide. MBM 020922 (3 spec.), YS, R/V Yancheng, Sta. 3071, 34°30’N, 121°00’E, 21 m, brown silt, coll. Zongguo Huang, 22 Jul. 1959. 16.2–23.4 mm long, 7.8–8.2 mm wide; abdomen 7.7–10.6 mm long; left shield plate 2.7–3.4 mm long, 2.5–3.1 mm wide. MBM 020986 (2 spec.), YS, R/V Yuzheng III, Sta. 3015, 36°30’N, 121°30’E, 29 m, brown mud, 28 Oct. 1958. MBM 021000 (1 juv.), YS, R/V Yancheng, Sta. 3061, 35°00’N, 121°30’E, 30.4 m, muddy sand, coll. Lingxin Lv, 25 Oct. 1958.

Description. Holotype (MBM283058) complete ( Fig. 4 A). Body pale to yellowish, introvert fully exposed, with similar pigmentation as abdomen, constriction or waist segments relaxed. Introvert covered by minute papillae, abdomen with clusters of cuticular papillae in rows on posterior abdomen. Body 33.5 mm long, 11.0 mm wide; abdomen 20.6 mm long; left ventro-caudal shield plate 4.3 mm long, 3.4 mm wide.

Prostomium hemispherical, projected, translucent pale. Eyespots not seen. Boundary area behind prostomium distinct, with lateral rounded ridges ( Fig. 4 B). Peristomium whitish, flat, barely extended laterally and ventrally to margin of first chaetiger; covered by minute papillae (papillae eroded in some specimens) ( Fig. 4 B). Mouth circular, projected, slightly wider than prostomium, covered by minute papillae ( Fig. 4 B).

First three chaetigers with 14–17 translucent yellow, falcate hooks; hooks gradually smaller from dorsum to ventrum; tapered with mucronate or blunt tips, without subdistal darker areas ( Fig. 4 C). Genital papillae tapered with truncate tips, protruding ventrolaterally from intersegmental groove between segments 7 and 8. Anterior abdomen with 7 segments ( Fig. 4 A), with minute papillae evenly distributed on the ventral side. Well defined clusters of papillae arranged in row, encircling each segment from lateral side to dorsum. Capillaries not seen.

Ventro-caudal shield slightly sclerotized, slightly soft, with a thick layer of firmly adhered sediment particles, looking dusty; yellow to orange, with concentric lines and radial ribs ( Fig. 4 E–I). Anterior margins angular or slightly rounded, anterior depression deep, anterior keels covered by white integument layer. Suture restricted to anterior region. Lateral margins rounded or barely straight, smooth, with distinct posterolateral corners in larger specimens. Main ribs prominent, concentric lines raised near margin ( Fig. 4 E–H). Fan reaching or slightly expanded beyond posterolateral corners, margin continuous, smooth, without distinct median notch ( Fig. 4 E–I).

Marginal chaetae including 10 lateral fascicles and 5 posterior ones ( Fig. 4 F, I). Lateral fascicles gradually becoming longer posteriorly, last two bundles closer to each other, chaetae arranged in shallow curve. Posterior fascicles similar in length, chaetae in linear arrangement. Peg chaetae tapered, with stout base in cross section. A small fascicle of very delicate capillary chaetae, 2–3 times longer than those present in posterior-most bundle, between peg chaetae and last fascicle of lateral chaetae. Another fascicle of short delicate capillary between peg chaetae and first posterior fascicle, three times longer than posterior chaetae.

Branchiae abundant ( Fig. 4 A), protruding from two divergent plates. Branchial filaments long, slender, curled or spiraled; interbranchial papillae long, white, more slender than branchial filaments, often with fine sediment particles. Branchial plates short, distally expanded, rounded ( Figs 4 D, 5E).

Variation. Ventro-caudal shield varies in three aspects. First, the concentric lines are usually prominent near the shield margin ( Fig. 4 E–H), but they can be faint in some smaller specimens ( Fig. 4 I). Second, the lateral margins can be variably developed, rounded and expanding laterally in small individuals ( Fig. 4 I), and barely straight with distinct posterior corners in the larger ones ( Fig. 4 F, G). Third, the fan margins are usually truncate and at the same level as the posterior corners, but can also be slightly expanded posteriorly with a shallow, irregular median depression ( Fig. 4 E, G, H).

Juvenile shields. The specimens illustrated in figure 5 have a relatively small body size and a morphologically different shield, and are regarded as juveniles. The ventro-caudal shields are less sclerotized, softer than those of adults, and thus their sediment cover is harder to be brushed off ( Fig. 5 F). The lateral margins are rounded and expanded laterally. The posterior margins are truncate without a median notch. The main radial ribs are obvious in most juveniles but the concentric lines are not so distinct. When the body size increases, annulated concentric bands appear ( Fig. 5 G) and even protrude in the fan ( Fig. 5 F).

Etymology. Sternaspis liui is named to honor the late Professor Ruiyu Liu, in recognition of his great contributions to benthic taxonomy, and in appreciation of his mentoring and guidance to the first author.

Distribution. The Yellow Sea (21–43.3 m) ( Fig. 1 ).

Remarks. The ventro-caudal shield of Sternaspis liui sp. nov. is slightly sclerotized, with a more or less soft consistency, and carries firmly adhered sediment particles, especially in smaller specimens. These features give the species a superficial resemblance to members of Caulleryaspis Sendall & Salazar-Vallejo, 2013 . However, Caulleryaspis species have very soft shields with sediment cover that cannot be brushed off, and the shield features are so poorly developed that there are no ribs or concentric lines. By contrast, the shield of Sternaspis liui sp. nov. is slightly soft with sediment cover that can be removed with the aid of fine-pointed forceps, and both the ribs and concentric lines are well defined. These characters indicate the new species should be classified into the genus Sternaspis , although members of Sternaspis usually have stiff shields with a sediment cover easily brushed off.

Like Sternaspis chinensis described above, S. liui sp. nov. is a species that has also been misidentified as S. scutata ( Ranzani, 1817) in China since the 1950s. This is largely due to underestimation of shield morphology in the taxonomy of Sternaspis . Actually, Sternaspis liui sp. nov. is readily distinguished from S. scutata and S. chinensis by their shield features. The former has a slightly soft shield with firmly adhered sediment, and the main ribs prominent and concentric lines raised near the margin, while shields of the latter two are stiff with sediment easily brushed off, and their main ribs and concentric lines are not prominent.

Sternaspis liui sp. nov. resembles S. maior Chamberlin, 1919 , a species originally described from the Eastern Pacific, in having prominent main radial ribs. The new species can be distinguished by possessing the concentric lines which are barely visible in S. maior . They also differ in their distribution, since S. maior is found in the Gulf of California, off the west coast of the Baja California Peninsula and Guerrero off the west coast of Mexico ( Sendall & Salazar-Vallejo 2013; Méndez & Yáñez-Rivera, in press), while S. liui sp. nov. is only known from the Yellow Sea.

Further, S. liui sp. nov. is unique in the genus by a combination of characters as follows: the shields are slightly sclerotized and firmly adhered by sediment, appearing dusty in frontal view; the main radial ribs are distinct, forming an obvious boundary between the lateral shield plates and the fan; and the concentric lines are welldefined and even prominent near the margin.

Figures

FIGURE 1. Distribution of Sternaspis chinensis sp. nov. and S. liui sp. nov. in the sea areas of China based on the examined material.

FIGURE 4. Sternaspis liui sp. nov. A, B, G: Holotype (MBM 283058); C – F, H – I: Five paratypes from MBM 283059. A. Complete specimen in ventral view; B. Anterior end in frontal view; C. Introvert hooks of first three chaetigers; D. Branchial plates, branchiae removed; E – I. Ventro-caudal shield in frontal view. Scale bars. A: 5 mm, B: 2 mm, C – H: 1 mm.

FIGURE 5. Juveniles of Sternaspis liui sp. nov. A. Five paratypes (A 1 – A 5) from MBM 283059; Ventro-caudal shield: B. from specimen A 1; C. from specimen A 2; D. from Specimen A 3; F. from MBM 020934, sediment cover not removed; G. from specimen A 4; E. Branchial plates, branchiae removed. Scale bars. A: 5 mm, B – G: 1 mm.