Sternaspis thalassemoides Otto, 1821, reinstated

Sendall, Kelly & Salazar-Vallejo, Sergio I., 2013, Revision of Sternaspis Otto, 1821 (Polychaeta, Sternaspidae), ZooKeys 286, pp. 1-74 : 18-20

Sternaspis thalassemoides Otto, 1821, reinstated Figures 1B4

Sternaspis thalassemoides Otto, 1821: 619-627, Pl. 50, figs 1-5; delle Chiaje 1822:Pl. 62, fig. 18 (upside down; no details of shield or chaetae), 1831: 204 (legend for plate 62, figure 18), 1841 (3): 76-79, Pl. 43 (legend for plate 62, figure 4), Pl. 94 (for plate 84), Pl. 106 (for plate 62, figure 18); Krohn 1842: 426-432; de Quatrefages 1866: 590-591; Goodrich 1897: 233-245, Pls. 15-16, figs 1-24.

Sternaspis scutata : Vejdovský 1882: 33-90, Pls. 1-10; von Marenzeller 1890: 5-8, Pl. 1, fig. 6 (non Ranzani 1817).

Sternaspis assimilis Malmgren, 1867: 195-196.

Type material.

Italy, Tyrrhenian Sea, Naples. Neotype (ZMUC POL-2159) and 3 paraneotypes (ZMUC POL-2160), 1928, no further data.

Additional material.

Italy. Tyrrhenian Sea, Bay of Naples. 3 spec. (ANSP 1880). 1 spec. (SMNH 50759). Adriatic Sea. 2 spec. (ECOSUR 2642), Sta. 167 (no coord.), 1-VIII-1966. 1 spec. (ECOSUR 2644), Sta. 151 (no coord.), 1966.

Description.

Body colour off-white or grey in alcohol (Fig. 4 A–D); papillae minute, especially behind segment 7 and near shield on dorsal side, or smooth, apparently without papillae. Anterior region often swollen and bulbous, sometimes wider than posterior region, with a constriction at septum between segments 7 and 8 (Fig. 4D). Neotype 14.6 mm long (paraneotypes 11.9-17.0 mm long), 12 mm wide, with about 30 segments.

Prostomium small, without eyespots. Peristomium rounded, flattening at position of the mouth and devoid of any papillae. Mouth circular, completely covered with minute papillae, extends from prostomium to the edge of segment 2 (Fig. 4D).

First three chaetigers with more than 12-14 hooks, bronze with subdistal dark band (Fig. 4E). Genital papillae between segments 7-8 (Fig. 4 B–D). Pre-shield region with 7 segments, sometimes bearing small fascicles of fine capillary chaetae.

Ventro-caudal shield with radiating oblique ribs and concentric lines; suture restricted to anterior region (Figs 1B, 4B, C, F). Anterior margins rounded; anterior depression deep; anterior keels not exposed. Lateral margins slightly expanding posteriorly. Fan truncate, not extending beyond posterior corners, crenulated, slightly projected outwardly, especially in larger individuals; median notch shallow.

Marginal chaetal fascicles include 10 lateral ones, chaetae ovally arranged, and six posterior fascicles, chaetae in a slightly curved arrangement. First two lateral fascicles emerge from ventral edge of shield. Lateral fascicles with long hirsute chaetae. Peg chaetae not seen.

Branchiae spirally twisted, abundant, variably eroded (Fig. 4A, B, C, F).

Neotype locality.

Italy. Naples, Tyrrhenian Sea.

Remarks.

Sternaspis thalassemoides Otto, 1821 has not been recorded since the late 1800's and because it is currently regarded as a junior synonym of Sternaspis scutata Ranzani, 1817, the type species name disappeared from the literature around the turn of the twentieth century. However, Sternaspis thalassemoides is reinstated because it differs from Sternaspis scutata , especially regarding the development of the fan; in Sternaspis thalassemoides the fan is truncate, entire, reaching the level of the posterolateral corners, whereas it is notched and expanded beyond the posterolateral margins in Sternaspis scutata . On the other hand, Sternaspis assimilis has been regarded as a junior synonym of Sternaspis scutata , but their shields are very different, and Sternaspis assimilis shield is more similar to the one of Sternaspis thalassemoides because their fan is slightly projected. It would be useful to evaluate the size variation among topotype specimens from the English Channel to ratify or correct this synonymy. Although Otto described the shield as blue-black, the colour varies among most sternaspid species intraspecifically and a few of the 8 individuals had a more typical rust-red coloured shield.

A neotype for Sternaspis thalassemoides Otto, 1821 is proposed because this is the type species for Sternaspis Otto, 1821 and there are two species in the Mediterranean Sea which have been poorly defined. Further, the lack of type materials and of an adequate description has resulted in confusion such that the species has been regarded as a junior synonym for the other regional species, Sternaspis scutata (Ranzani, 1817); the neotype and its description will clarify the taxonomic status of the species ( ICZN 1999, Art. 75.3.1-75.3.3). The original material was either not deposited or destroyed, and our queries to collection managers in major European museums concluded that this species has no type material ( ICZN 1999, Art. 75.3.4). The original description was brief but the illustrations show a ventro-caudal shield with a straight posterior margin ( Otto 1821, fig. 1), which is consistent with the specimen selected as neotype ( ICZN 1999, Art. 75.3.5). The proposed neotype was collected in the type locality, Naples ( ICZN 1999, Art. 75.3.6), and it has been deposited in the Zoological Museum of the Copenhagen University ( ICZN 1999, Art. 75.3.7).

The shield of Sternaspis thalassemoides has a posterior margin straight, equal in posterior extension to posterolateral corners resembling Sternaspis princeps , Sternaspis rietschi , Sternaspis spinosa and Sternaspis thorsoni sp. n.; however, Sternaspis spinosa can be separated from the others because its shield is much wider than long and by having its anterior keels exposed. Further, Sternaspis thorsoni can be separated from the others by having more abundant, straw-coloured, delicate introvert hooks, whereas the remaining species have fewer, thicker, darker hooks. Because there are no concentric lines in their shield, Sternaspis princeps can be distinguished from Sternaspis thalassemoides and Sternaspis rietschi . These two species differ because in Sternaspis thalassemoides the shield lateral margins are almost straight, not markedly expanded medially, whereas in Sternaspis rietschi they are rounded, markedly expanded medially.