Sternaspis thorsoni, Sendall, Kelly & Salazar-Vallejo, Sergio I., 2013

Sendall, Kelly & Salazar-Vallejo, Sergio I., 2013, Revision of Sternaspis Otto, 1821 (Polychaeta, Sternaspidae), ZooKeys 286, pp. 1-74 : 46-48

Sternaspis thorsoni sp. n. Figure 15

Sternaspis scutata : Wesenberg-Lund 1949: 345-346 (non Ranzani 1817), Fauvel 1932: 213 (non Ranzani 1817, partim).

Type material.

Arabian (Iranian or Persian) Gulf. Holotype (ZMUC 2221), 55.6 km NNW of buoy near Jask, Iran, Sta. 76 (25°45'N, 57°12'E), 110 m, loose, brown clay, 21-IV-1937, G. Thorson, coll. 6 paratypes: 1 (ZMUC 2222), juvenile, 4 km S Bushire outer Light-buoy, Sta. 28 (no coord.), 7 m, 18-III-1937, G. Thorson, coll. 1 (ZMUC 2223), juvenile, Henjom Island, Strait of Hormuz, Sta. 59 (26°36'N, 55°42'E), 31 m, 10-IV-1937, G. Thorson, coll. 1 (ZMUC 2224), adult, Patrick Steward Bank, Sta. 71B (26°41'N, 56°16'E), 69 m, gray mud, 19-IV-1937, G. Thorson, coll. 3 spec. (ZMUC 2225), juveniles, 17 km SSE off mountain Kuh-i-Namak Sar range, Sta. 114 (27°00'30N, 56°03'E), 13 m, sand with little clay, 4-IV-1938, G. Thorson, coll.

Additional material. Arabian (Iranian or Persian) Gulf. 1 spec. (ZMUC), juvenile, 3 km SSW off Kharg, Sta. 8 (29°14'N, 50°19'E), 40 m, soft, grey clay, 5-III-1937, G. Thorson, coll. 8 spec. (ZMUC), juveniles, partly dehydrated, 5.5 km SE Bushire outer Light-buoy, Sta. 28 (no coord.), 7 m, grey-brown clay, 18-III-1937, G. Thorson, coll. 3 spec. (ZMUC), juveniles, off road to Bender Abbas, Sta. 64B (no coord.), 3 m, soft clay, 16-IV-1937, G. Thorson, coll. 3 spec. (ZMUC), juveniles, off road to Bender Abbas, Sta. 64Bx, 3 m, soft clay, 16-IV-1937. 2 spec. (ZMUC), 11 km ENE from Quishim Light-buoy, Sta. 65 (27°01'N, 56°00'E), 18 m, dark sand with clay, 16-IV-1937, G. Thorson, coll. Andaman Sea. 5 spec. (MNHN 454), Andaman Islands, no further data.

Description.

Holotype with body whitish or grayish (Fig. 15A), introvert slightly darker, integument granulose; abdomen smooth. Papillae minute, abundant, short and longer, filiform, uniformly distributed especially on abdomen. Body 14 mm long, 5 mm wide, with about 30 segments.

Prostomium small, without eyespots. Peristomium rounded, depressed below mouth, without papillae (Fig. 15B). Mouth circular, completely covered with minute papillae, continued ventrally forming an arc.

First three chaetigers with 16-20 hooks, thin, pale with a subdistal barely darker band (Fig. 15B). Genital papillae protrude ventrally from intersegmental groove between segments 7 and 8. Pre-shield region with 7 segments, without fascicles of fine capillary chaetae.

Ventro-caudal shield previously sliced along posterior right corner, with radiating oblique ribs and concentric lines; suture restricted to anterior region (Fig. 15A, C). Anterior margins angular; anterior depression deep; anterior keels visible, but not exposed. Lateral margins slightly expanding posteriorly. Fan truncate, not extending beyond posterior corners, crenulated, not projected outwardly; median notch shallow or indistinct.

Marginal chaetal fascicles include 10 lateral ones, chaetae ovally arranged, and seven posterior fascicles, chaetae in a slightly curved arrangement. First two lateral fascicles emerge from ventral edge of shield. Lateral fascicle with long hirsute chaetae. Peg chaetae in posterior corner region.

Branchiae mostly removed, spirally arranged.

Type locality.

Off Jask, Iran.

Variation.

Smaller paratypes have better defined body papillae which are larger, especially on abdominal segments. Likewise, paratypes exhibit ventro-caudal shields which are rounded without surface features in smaller specimens (Fig. 15D), with a suture well defined but little definition of anterior margins and reduced development of posterior corners. Larger specimens show better definition of anterior margins and more developed posterior corners, together with crenulations of the fan margin, but concentric lines are not well-defined (Fig. 15E). Larger specimens have all surface ornamentation features, together with well defined acute anterior margins and posterior corners extended beyond the fan level, and more definite resolution of fan crenulations (Fig. 15F) than smaller specimens.

Etymology.

The species name is derived after the late Dr. Gunnar Thorson in recognition of his important contributions to benthic ecology, especially with regards to reproduction and larval development ( Thorson 1946, 1950), and comparative studies of benthic communities where he coined the concept of parallel communities ( Thorson 1957). He also made many collecting trips in temperate and tropical communities and the specimens used for this description were based on his collections. The epithet is a noun in the genitive case.

Remarks.

The shield of Sternaspis thorsoni sp. n.has a truncate posterior margin resembling Sternaspis princeps , Sternaspis rietschi , Sternaspis spinosa and S thalassemoides . As indicated above, Sternaspis spinosa is characterised by having a shield markedly wider than long and by having exposed its anterior keels. Further, Sternaspis thorsoni is unique as it has more abundant, pale delicate introvert hooks, whereas the other species have fewer, thicker, darker hooks.

Fauvel (1932: 213) indicated three shield colour variants. The only specimens available, collected in the Andaman Islands, are all conspecific and almost completely fit this new species description, although the larger specimen has a marked notch on the shield’s fan.

Distribution.

Arabian Sea, in muddy bottoms in shallow water (3-110 m). Probably reaching as far as the Andaman Sea.