Sternaspis chinensis, 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 : 374-379

Sternaspis chinensis sp. nov.

Figs 1–3

Sternaspis scutata: Kao et al., 1959: 164 , Pl. 17, Fig. 2 ; Yang & Sun, 1988: 251, Fig. 117 (non Ranzani, 1817).

Type material. Holotype: MBM 020940, BS, R/V Handan, Sta. 1054, 38°38’N, 120°23’E, 39 m, brown silt, coll. Jinxiang Jiang, 25 Oct. 1959. Paratypes: MBM283055 (5 spec.), same collecting information as the holotype. Three anterior ends retracted, 20.3–25.5 mm long, 7.1–12.2 mm wide; abdomen 11.6–20.5 mm long; left shield plate 3.4–5.0 mm long, 3.1–4.5 mm wide. MBM283056 (7 spec.), YS, R/V Kexue III, Sta. 124-4B, 33°00’N, 124°00’E, 50 m, hard mud, 13 Jul. 2011. 21.8–24.3 mm long, 9.2–11.0 mm wide; abdomen 14.0– 16.1 mm long; left shield plate 3.5–4.0 mm long, 3.7–4.1 mm wide. MBM283057 (1 spec.), YS, R/V Kexue III, Sta. B-7A, 37°40’N, 122°27’E, 27 m, mud, 22 Nov. 2010. Anterior end retracted, 5.4 mm wide; abdomen 9.1 mm long; left shield plate 2.5 mm long, 2.1 mm wide. MBM283068 (11 spec.), YS, R/V Kexue III, Sta. 3700B, 37°00’N, 122°59’E, 29.8 m, 16 Jul. 2011. MBM 020711 (1 spec.), R/V Handan, Sta. 2018, 37°37’N, 122°06’E, 31 m, brown mud, coll. Mu Chen, 14 Jul. 1959.

Additional material. Bohai Sea. MBM 020988 (2 spec.), R/V Handan, Sta. 1084, 37°45’N, 120°15’E, 13 m, brown mud. MBM 020973 (1 spec.), R/V Jinxing, Sta. 1045, 38°53’N, 117°53’E, 56 m, brown fine sand, coll. Yuheng Cui, 2 Nov. 1958. MBM 020923 (1 juv.), R/V Yancheng, Sta. 1084, 38°45’N, 120°15’E, 15 m, brown sandy mud, 28 Jan. 1959. MBM 020939 (1 spec.), R/V Handan, Sta. 1077, 37°48’N, 119°45’E, 18.6 m, brown sandy mud, coll. Mu Chen, 24 Jul. 1959. MBM 020982 (5 juv.), R/V Yancheng, Sta. 1046, 38°53’N, 117°53’E, 8 m, brown mud, 30 Apr. 1959. MBM 020983 (3 juv.), R/V Yancheng, Sta. 1082, 37°45’N, 119°54’ E, 17 m, brown mud, 4 May 1959. MBM 020984 (4 juv.), R/V Yancheng, Sta. 1084, 37°45’N, 120°15’E, 15 m, brown mud, 3 May 1959. MBM 020985 (3 juv.), R/V Yancheng, Sta. 1077, 37°48’N, 119°45’E, 20 m, yellow sandy mud, coll. Mu Chen, 4 May 1959. MBM 020987 (1 spec.), R/V Handan, Sta. 1082, 37°45’N, 119°45’E, 15.8 m, brown sandy mud, coll.

Jinxiang Jiang. MBM 021011 (1 juv.), R/V Yancheng, Sta. 1027, 39°6’N, 121°21’E, 10 m, yellow sandy mud, coll. Zongguo Huang, 27 Apr. 1959. Yellow Sea. MBM 020938 (2 spec.), R/V Handan, Sta. 2040, 38°29’N, 122°36’E, 37 m, brown silt, coll. Jinxiang Jiang, 19 Oct. 1959. MBM 020981 (2 spec.), R/V Yancheng, Sta. 3002, 37°15’N, 123°00’E, 30 m, brown mud, coll. Gongyi Hu, 20 Oct. 1959. MBM 020989 (17 spec.), R/V Handan, Sta. 2016, 37°34’N, 121°41’E, 23 m, brown sandy mud, coll. Jinxiang Jiang, 14 Jul. 1959. MBM 020919 (1 spec.), R/V Yancheng, Sta. 2033, 38°43’N, 122°12’E, 23.7 m, brown mud, coll. Mu Chen, 22 Apr. 1959. MBM 020935 (6 spec.), R/V Handan, Sta. 2058, 38°00’N, 123°30’E, 23 m, fine sand, 9 Jul. 1959. MBM 020936 (11 spec.), R/V Handan, Sta. 2062, 37°30’N, 123°00’E, 47.8 m, brown sandy mud, coll. Jinxiang Jiang, 12 Jul. 1959. MBM 020937 (1 spec.), R/V Handan, Sta. 2016, 37°34’N, 121°41’E, 23 m, brown fine sandy mud, coll. Jinxiang Jiang, 14 Jul. 1959. MBM 020918 (2 spec.), R/V Yancheng, Sta. 2012, 37°48’N, 121°43’E, 31 m, brown mud, coll. Mu Chen, 23 Apr. 1959. MBM 020996 (5 juv.), R/V Jinxing, Sta. 2033, 38°43’N, 122°12’E, 25 m, mud, coll. Guangyu Lin, 19 Oct. 1958. MBM 020997 (1 juv.), R/V Yuzheng III, Sta. 3004, 37°00’N, 122°45’E, 29 m, brown mud, 29 Oct. 1958. MBM 020998 (11 juv.), R/V Jinxing, Sta. 2043, 39°15’N, 123°13’E, 15 m, brown fine sand, coll. Yongliang Wang, 14 Sep. 1958. MBM 020999 (1 juv.), R/V Jinxing, Sta. 2016, 37°34’N, 121°41’E, 28 m, hard sandy mud, coll. Yuheng Cui, 18 Oct. 1958. MBM283060 (12 spec.), R/V Kexue III, Sta. 1098B, 38°41’N, 121°17’E, 63 m, gravel, 12 Jul. 2010. MBM283061 (3 spec.), R/V Kexue III, Sta. 3700B, 36°56’N, 123°00’E, 28.5 m, mud, 21 Nov. 2010. 30.6 mm long, 7.5–8.9 mm wide; abdomen 12.1–18.8 mm long; left shield plate 3.0– 4.1 mm long, 3.1–3.8 mm wide. MBM283062 (1 spec.), R/V Kexue III, Sta. 3500-4B, 35°00’ N, 121°08’E, 48 m, find sand and gravel, 30 Nov. 2010. Anterior end retracted, 10.6 mm wide; abdomen 16.0 mm long; left shield plate 3.7 mm long, 3.7 mm wide. MBM283063 (3 juv.), R/V Kexue III, Sta. 3600-1A, 36°00’ N, 120°30’E, 35.7 m, silt, 20 Nov. 2010. All anterior ends retracted, 2.8–3.0 mm wide; abdomen 3.5–4.1 mm long; left shield plate 0.9–1.1 mm long, 1.8–1.9 mm wide. MBM283064 (1 juv.), R/V Kexue III, Sta. CJ-5A, 32°12’ N, 124°06’E, 43.1 m, mud, 27 Nov. 2010. MBM283065 (1 juv.), R/V Kexue III, Sta. CJ-5A, 32°11’N, 124°00’E, 42.3 m, mud, 13 Jul. 2011. 4.8 mm long, 2.2 mm wide; abdomen 3.2 mm long; left shield plate 0.8 mm long, 0.8 mm wide. MBM283066 (3 spec.), R/V Kexue III, Sta. CJ-5B, 32°10’N, 124°00’E, 42.9 m, mud, 13 Jul. 2011. 10.0–20.0 mm long. MBM283067 (1 juv.), R/V Kexue III, Sta. 3700A, 37°00’N, 123°00’E, 29.7 m, 16 Jul. 2011. Anterior end retracted, 4.0 mm wide; abdomen 6.0 mm long; left shield plate 1.2 mm long, 1.2 mm wide. MBM283069 (3 spec.), R/V Kexue III, Sta. 3875-3A, 38°45’N, 122°59’E, 56.3 m, sandy mud, 15 Jul. 2011. MBM283070 (4 spec.), R/V Kexue III, Sta. 3875-3B, 38°45’N, 123°00’E, 56.7 m, 15 Jul. 2011. MBM283071 (2 spec.), R/V Kexue III, Sta. B-7A, 37°40’N, 122°27’E, 28.3 m, mud, 16 Jul. 2011. MBM283072 (1 spec.), R/V Kexue III, Sta. 3300-2B, 33°00’ N, 123°01’E, 34.2 m, 13 Nov. 2011. Anterior end retracted, 7.0 mm wide; abdomen 12.8 mm long; left shield plate 3.2 mm long, 3.2 mm wide. MBM283073 (1 spec.), R/V Kexue III, Sta. 1098-1B, 38°41’ N, 121°18’E, 63.7 m, 16 Nov. 2011. Anterior end retracted, 5.4 mm wide; abdomen 10.1 mm long; left shield plate 2.3 mm long, 2.3 mm wide. MBM283074 (1 juv.), R/V Kexue III, Sta. CJ-5A, 32°10’N, 123°59’E, 42.5 m, hard mud, 13 Nov. 2011. Anterior end retracted, 2.8 mm wide; abdomen 4.9 mm long; left shield plate 1.0 mm long, 1.0 mm wide. MBM283075 (1 juv.), R/V Kexue III, Sta. 3875-3A, 38°45’N, 123°00’E, 55.3 m, slit, 16 Nov. 2011. MBM283076 (2 spec.), R/V Kexue III, Sta. B- 7A, 37°40’N, 122°27’E, 28.1 m, mud, 16 Nov. 2011. MBM283077 (2 spec.), R/V Kexue III, Sta. 3600-2B, 35°59’N, 121°00’E, 34.8 m, silt, 17 Nov. 2011. MBM283078 (1 spec.), R/V Kexue III, Sta. 3500-2A, 34°59’N, 120°01’E, 27.4 m, mud, 11 Nov. 2011. 35.1 mm long, 11.0 mm wide; abdomen 21.1 mm long; left shield plate 4.0 mm long, 3.7 mm wide. MBM283079 (12 spec.), R/V Kexue III, Sta. 3700B, 37°00’N, 123°00’E, 29.8 m, 17 Nov. 2011. East China Sea. MBM 020977 (2 spec.), R/V 625, Sta. 4115, 31°45’N, 122°45’E, 30 m, mud, coll. Guangyu Lin, 21 Jul. 1959. 14.1 mm long, 7.8 mm wide; abdomen 8.8–12.0 mm long; left shield plate 2.9–3.1 mm long, 2.6–3.0 mm wide. MBM 020980 (1 spec.), R/V D, Sta. 4111, 31°00’N, 122°45’E, 28 m, brown mud, 13 Apr. 1959. MBM 020941 (2 spec.), R/V Handan, Sta. 4111, 31°00’N, 122°45’E, 26.6 m, mud, coll. Liren Cheng and Jingzuo Qu, 10 Dec. 1959. MBM 020975 (1 spec.), R/V C, Sta. 4024, 32°30’N, 122°15’E, 25.5 m, brown fine sand, coll. Jinzhao Zhu and Jieshan Xu, 22 Oct. 1959. MBM 020943 (3 spec.), R/V Handan, Sta. 4115, 31°45’N, 122°45’E, 27 m, mud, coll. Liren Cheng and Jingzuo Qu, 6 Dec. 1959. MBM 020967 (3 spec.), R/V 401, Sta. 4133, 29°30’N, 122°45’E, 54 m, sandy mud, coll. Liren Cheng, 10 Jul. 1959. MBM 020968 (1 spec.), R/V 401, Sta. 4059, 29°15’N, 122°30’E, 46 m, mud, 12 Jul. 1959. MBM 020970 (1 spec.), R/V 401, Sta. 4124, 30°15’N, 122°30’E, 28 m, mud, 8 Apr. 1959. MBM 020976 (2 spec.), R/V 828, Sta. 4133, 29°30’N, 122°45’E, 50 m, sandy mud, 26 Oct. 1959. MBM 020969 (2 spec.), R/V 401, Sta. 4115, 31°45’N, 122°45’E, 29 m, mud, 5 Apr. 1959. MBM 020966 (2 juv.), R/ V 401, Sta. 4123, 30°15’N, 122°00’E, 10 m, yellow mud, coll. Yuheng Cui, 9 Apr. 1959. MBM 020972 (2 spec.), R/V Jinxing, Sta. 4122, 31°30’N, 123°00’E, 59 m, brown sandy mud, coll. Yuheng Cui, 4 Feb. 1959. MBM 020979 (4 spec.), R/V D, Sta. 4121, 31°30’N, 122°45’E, 43 m, mud, coll. Yuheng Cui, 8 Apr. 1959. MBM 021002 (1 spec.), R/V Jinxing, Sta. 4111, 31°00’N, 122°45’E, 28 m, brown mud, coll. Liren Cheng, 2 Feb. 1959. MBM 021010 (1 spec.), R/V 401, Sta. 4116, 31°30’N, 121°30’E, mud, coll. Jixing Liu, 9 Apr. 1959. MBM 021001 (19 spec.), R/V Handan, Sta. 4111, 31°00’N, 122°45’E, 26.6 m, mud, coll. Liren Cheng and Jingzuo Qu, 10 Dec. 1959.

Description. Holotype (MBM 020940) complete. Body pale to yellowish, introvert fully exposed, with similar pigmentation as abdomen, constriction or waist segments relaxed ( Fig. 2 A). Introvert mostly smooth, abdomen finely papillose. Body 25.5 mm long, 9.2 mm wide, abdomen 15.5 mm long; left ventro-caudal shield plate 3.9 mm long, 3.8 mm wide.

Prostomium hemispherical, projected, whitish. Eyespots not seen. Inverted U-shaped boundary behind prostomium ( Fig. 2 B). Peristomium round, with few papillae, barely extended laterally and ventrally to margin of first chaetiger. Mouth circular, projected, wider than prostomium, covered by minute papillae (papillae eroded in some specimens) ( Fig. 2 A, B).

First three chaetigers with 14–16 light yellow to yellow, falcate hooks. Hooks tapered with mucronate tips, becoming very small in ventral side, without subdistal darker areas ( Fig. 2 B, C). Genital papillae digitate, protruding ventrolaterally from intersegmental groove between segments 7 and 8. Anterior abdomen with 7 segments ( Fig. 2 A), papillae minute, evenly distributed on the ventral side. Well defined clusters of papillae arranged in a row, encircling each segment from lateral side to dorsum. Capillaries not seen.

Ventro-caudal shield reddish-orange or brick red, usually darker in central areas; concentric bands markedly annulated, ribs distinct ( Fig. 2 E–H). Anterior margins angular or slightly rounded, anterior depression deep, anterior keels covered by translucent integument layer. Suture visible throughout shield or fused in posterior region. Lateral margins slightly rounded, smooth, with distinct posterolateral corners. Fan reaching or slightly expanded beyond posterolateral corners, margin crenulated; median notch wide and shallow ( Fig. 2 E–H).

Marginal chaetae including 10 lateral fascicles and 5 posterior ones ( Fig. 2 E–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 tapered, with stout base in cross section. A small fascicle of delicate capillary chaetae, 2–3 times longer than those present in posterior-most bundle, between peg chaetae and last fascicle of lateral chaetae.

Branchiae abundant ( Fig. 2 A), protruding from two divergent plates. Branchial filaments long, slender, curled or spiraled; interbranchial papillae long, curled, often with fine sediment particles. Branchial plates long, V-shaped, distal portion rounded, expanded laterally ( Fig. 2 D).

Variation. There are several variations in the pigmentation and shape of the ventro-caudal shield. The pigmentation is mainly reddish-orange in small specimens ( Fig. 2 F, H), and becomes brick red or red-brownish in larger ones ( Fig. 2 E, G). The shape of the shield is generally stable with three variations. First, most individuals have a wide and shallow depression in the fan margin, while some smaller ones have a relatively deep notch ( Fig. 2 F, H), and some larger ones have an almost straight margin without a distinct depression ( Fig. 2 E). Second, the posterior margins usually reach or are slightly expanded beyond the posterolateral corners, but in rare cases they are clearly expanded beyond the posterolateral corners ( Fig. 2 F). Third, most individuals have a visible suture throughout the shield, but the suture is fused in the posterior region in some larger specimens.

Juvenile shields. The specimens ( Fig. 3 ) with a smaller body size (generally less than 5 mm in width) and a relatively thin shield are herein regarded as juveniles. Their shields show a reddish-orange pigmentation and the concentric bands are poorly defined ( Fig. 3 B–F). The lateral margins are slightly rounded without distinct posterolateral corners, and the sutures are distinct throughout the shield. The smallest specimens, being 2–3 mm wide, have a rounded anterior margin with a shallow anterior depression and an exposed anterior keel, and the posterior margin is medially projected ( Fig. 3 B). With increasing body size, the shields change in three aspects: the anterior depression becomes deeper and the keel increases to up to half as long as the depression ( Fig. 3 D–F); the radial stripes appear and the main ribs become distinct; and the median notch in the fan margin gradually becomes distinct ( Fig. 3 E–F).

Etymology. The species name is an adjective in the nominative singular, derived from China, with the Latin suffix - ensis to indicate the Chinese seas, where the species is widely distributed.

Distribution. The Bohai Sea (8–56 m), Yellow Sea (23–63.7 m) and East China Sea (10–54 m) ( Fig. 1 ).

Remarks. Since the 1950s, all specimens of Sternaspis chinensis sp. nov. collected from the sea areas of China have been identified as S. scutata ( Ranzani, 1817) , a species originally described from the Mediterranean Sea. Both species have a shield with distinct radial ribs and concentric lines, deep anterior depression, rounded lateral margins and shallow median notch. However, S. chinensis differs from S. scutata by possessing concentric bands on the shield (vs. absent) and the crenulated posterior margin reaching or slightly expanded beyond the posterolateral corners (vs. posterior margin smooth and markedly expanded beyond the posterolateral corners). Besides, reliable records of S. scutata are only those from the Mediterranean Sea to the English Channel, and the specimens from non-Mediterranean or Northeastern Atlantic need to be re-evaluated ( Sendall & Salazar-Vallejo 2013). Our examination on all sternaspid specimens demonstrates the absence of the species in China seas. Thus, the record of S. scutata in China seas is a misidentification.

Sternaspis chinensis sp. nov. resembles S. affinis Stimpson, 1864 , originally described from the NE Pacific Ocean, in having distinct radial ribs and concentric bands on the ventro-caudal shield, a shallow median notch and posterior margin reaching or slightly expanded beyond the posterolateral corners. However, the two species differ in three features of the shield. First, S. chinensis sp. nov has a reddish-orange or brick red shield with markedly concentric bands from margin to center, whereas in S. affinis the shield is reddish-brown with concentric bands mainly found in the marginal and submarginal area. Second, the radial ribs are well-developed and the fan margin is crenulated in S. chinensis sp. nov., whereas in S. affinis the shield is slightly ribbed and the fan margin is usually smooth. Third, the anterior margin is angular in S. chinensis sp. nov. but rounded in S. affinis .

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 2. Sternaspis chinensis sp. nov. A. Holotype (MBM 020940) in ventral view; B. Anterior end of paratype (MBM 020711) in frontal view; C. Introvert hooks of first three chaetigers of paratype (MBM 020711); D. Branchial plates of a paratype (MBM 283055), branchiae removed; E – H. Ventro-caudal shield of the holotype (E) and paratypes (F-H, MBM 283068, MBM 283056 and MBM 283057, respectively). A. Scale bars. A: 5 mm, B – G: 1 mm, H: 0.5 mm.

FIGURE 3. Juveniles of Sternaspis chinensis sp. nov. A. Four specimens (A 1 – A 4) showing size differences from MBM 020989; Ventro-caudal shield: B. from MBM 283063; C. from specimen A 1; D. from specimen A 2; E. from specimen A 3; F. from specimen A 4. Scale bars. A: 2 mm, B, C: 0.2 mm, D, E: 0.5 mm, F: 1 mm.