Sternaspis costata von Marenzeller, 1879, emended

Sendall, Kelly & Salazar-Vallejo, Sergio I., 2013, Revision of Sternaspis Otto, 1821 (Polychaeta, Sternaspidae), ZooKeys 286, pp. 1-74 : 28-31

Sternaspis costata von Marenzeller, 1879, emended Figures 1B8

Sternaspis costata von Marenzeller, 1879: 142-143, Tab. 6, fig. 4; 1890: 5-8, Pl. 1, fig. 5; Sluiter 1890: 108-110;

Sternaspis scutata : Okuda 1936: 151-152, fig. 5; Takahashi 1938: 211, Textfig. 13; Imajima 1961: 94-95, Textfig. 10 a–c; Imajima and Hartman 1964: 310-311 (non Ranzani 1817).

Type material.

Japan. Neotype (CMNH ZW-120), Honshu Island, Chiba, Boso Peninsula, 25-V-1995.

Additional material.

Japan. 2 spec. (ANSP 1051), and 1 spec. (ANSP 1062), off Honshu, 1900. 18 spec. (CMNH ZW-502), Kyushu, Kumamota, Amakusa, Sakitu, 22-VII-1964. 1 spec. (CMNH ZW-514), Honshu Island, Sagami Bay, off Manazuru, 40-70 m. 1 spec. (CMNH ZW-515), Honshu Island, Sagami Bay, off Manazuru, 40-70 m. One spec. (CMNH ZW-617), Kyushu, Kumamota, Amakusa. 1 spec. (CMNH ZW-996), Honshu Island, Sagami Bay, Shimoda, 34°38'53"S, 138°57'07"E, 40 m. 8 spec. (NHMW 1568), Honshu Island, Nagoya Bay, 1877. Sakhalin Island, Russia. 5 spec. (ZIRAS 43188), Aniva Bay, RV Toporok, Sta. 47, 46°20.8'N, 142°34.8'E, 48 m, 21 Sep. 1947. Philippines. 1 spec. (AM W 27162), west coast of Marinduque Island, 13°30'00"S, 121°30'00"E.

Description.

Neotype (CMNH ZW-120) with body colour creamy white to yellow-white, sometimes more grey, with first six segments lighter, becoming darker when dried out (Fig. 8A). Cuticle mostly with short filamentous papillae, somewhat longer on segments seven and eight. Rows of clustered filamentous papillae usually in two loosely arranged, lateral rows per segment, more noticeable on posterior segments dorsal to ventro-caudal shield. Body up to 22 mm long, 10 mm wide, about 29 segments.

Prostomium small, hemispherical, slightly opalescent. Peristomium rounded, raised at mouth, with some papillae between mouth and prostomium. Mouth densely papillate, slightly oval, positioned halfway between prostomium and anterior edge of segment 2.

First three chaetigers with 10 bronze, slightly falcate, introvert hooks with about another five smaller hooks ventral to larger hooks. Hooks widely separated (widely apposed), with subdistal dark areas. One pair of genital papillae protrude ventrally from intersegmental furrow between segments 7 and 8. Pre-shield region with 7 segments, with small fascicles of fine short capillary chaetae laterally in some specimens.

Ventro-caudal shield dark orange, often covered with sediment; ribs and concentric lines visible; suture extended throughout the shield (Figs 1B, 8 B–E). Anterior margins rounded; anterior depression shallow; anterior keels not exposed. Lateral margins rounded, expanded posteriorly. Fan slightly projected posteriorly, markedly notched medially.

Marginal chaetal fascicles include 10 lateral ones, chaetae in a narrow oval arrangement, and five posterior fascicles in an offset linear arrangement; chaetae curving towards midline. Peg chaetae long, with a narrow base in cross section, emerge from cuticle almost at same level as margin of shield. Two additional groups of delicate chaetae between peg chaetae and first bundle of posterior shield chaetae.

Branchiae numerous, coiled and protrude from two plates widely separated dorsally.

Variation.

The specimens from the Sakhalin Island (Fig. 8 C–E) show that the posterior median notch is always wide, but there are some changes with size. For example, from smaller to larger specimens, the anterior corners become less prominent whereas the diagonal rib and the fan ribs become more prominent. The relative posterior extension of the fan tends to become reduced and in even larger specimens, it may disappear completely.

Neotype locality.

Honshu Island, Chiba, Boso Peninsula, Japan.

Remarks.

Sternaspis costata von Marenzeller, 1879 has a rather peculiar nomenclatural history because it was the same author who proposed the species who later concluded ( von Marenzeller 1890) it was a junior synonym of another species, Sternaspis scutata (Ranzani, 1817) originally described from the Mediterranean Sea. As stated below, these two species are different and the Japanese species must be clarified; consequently we propose and describe a neotype and provide illustrations for its diagnostic features ( ICZN 1999, Art. 75.3.1-75.3.3). Emil von Marenzeller worked in the Vienna Museum and was in charge of several invertebrate groups, including polychaetes; however, because he changed his mind about his own species, he might have sent away the apparently discarded type materials or destroyed them during dissection because Dr. Helmut Sattmann has informed us that there is no type material for this species ( ICZN 1999, Art. 75.3.4). Von Marenzeller made only two figures and a detailed description to emphasize that his new species differed by the relative rib development, and his illustration shows that the fan is truncate with a deep median notch and that the posterior shield corners are well-developed; these same features are shown by the neotype such that we regard it as consistent with the original description and illustrations ( ICZN 1999, Art. 75.3.5). The original type locality was Miya Bay, south of Nagoya, Honshu Islands, Eastern Japan and the neotype locality is the Boso Peninsula, Chiba, Eastern Japan, about 300 km away but along the same coast. Despite the fact that these two localities are not contiguous, they are very close to each other ( ICZN 1999, Art. 75.3.6), although there was no indication about depth or habitat for the original materials. The neotype has been deposited in the Coastal Branch of Natural History Museum and Insitute, Chiba, Japan ( ICZN 1999, Art. 75.3.7).

Despite von Marenzeller’s detailed description of the ventro-caudal shield of Sternaspis costata , and especially because he later regarded it as a junior synonym of Sternaspis scutata , it was not recorded under the original name. There is no close resemblance between these two species because they markedly differ in their shields. In Sternaspis costata the anterior margins are rounded, the lateral margins expanded medially, the posterior corners are angular, well-defined, and the fan is markedly notched medially. On the contrary, in Sternaspis scutata the anterior margins are truncate, the lateral margins are straight, barely expanded, the posterior corners are rounded, poorly defined, and the fan is barely notched medially, and projected beyond the posterior corners. Sternaspis costata is unique among the species in the genus because its shield fan is reduced along its median line, especially in larger specimens, such that the lateral fan portions are longer, reaching the posterior corners, but the median portion is very short, as if having a wide, deep median notch.

Distribution.

Southern Sakhalin Island (Russia), Japan, and the Philippines, 20-70 m depth. The record for estuarine environments in India (Southern 1921: 649-651, Pl. 20, fig. 5a, b) is questionable; the illustration resembles the species but there are some subtle differences. Therefore, we are doubtful about the distribution extending to estuarine waters in the Bay of Bengal.