Sternaspis fossor Stimpson, 1853, restricted

Sendall, Kelly & Salazar-Vallejo, Sergio I., 2013, Revision of Sternaspis Otto, 1821 (Polychaeta, Sternaspidae), ZooKeys 286, pp. 1-74 : 31-33

Sternaspis fossor Stimpson, 1853, restricted Figures 1B9

Sternaspis fossor Stimpson, 1853: 29, fig. 19; Verrill 1873: 606, Pl. 14, fig. 74; Webster and Benedict 1884: 725, 1887: 132; von Marenzeller 1890: 5-8, Pl. 1, fig. 4 A–B; Moore 1909: 144; Hartman 1944: 82, Pl. 33, fig. 15; Hartman 1965: 192.

Sternaspis scutata : Pettibone 1954: 309-310, fig. 35 a, b (partim, non Ranzani 1817)

Type material.

Northwestern Atlantic Ocean, Canada. Neotype (USNM 15543), 88 km E Cape Sable, Nova Scotia, 153 m, mud, 6 Oct. 1909, O. Bryant, coll.

Additional material.

Canada, Brunswick. 1 spec. (HMCS 9953670), Bocabec Bay, 45°10'N, 67°02'W, 22 m, 20-XII-1976. 1 spec. (HMCS 9953671), L’Etang Estuary, 45°04'30"N, 66°47'39"W, 20-VIII-1975. 37 spec. (HMCS 9953672), Letite Passage, 45°03'N, 66°55'W, 73 m (in codfish stomach), 7-V-1976. 5 spec. (HMCS 9953673), Passamaquoddy Bay, Loring Cove, 45°06'N, 66°59'W, 27-34 m, 22-V-1973. 12 spec. (HMCS 9953676), Bocabec Bay, 45°10'N, 67°02'W, 3-III-1977. 1 spec. (HMCS 9953677), Passamaquoddy Bay (Wolves-Lepreau), 1966. 4 spec. (USNM 7872), East of Grand Manan, 108 m, mud, 1872. U.S.A. Three spec. (ANSP 1247), off Newport, Rhode Island.

Description.

Neotype (USNM 15543) complete, most body papillae eroded but transverse rows still noticeable; introvert exposed (Fig. 9C); 9.7 mm long, 3.5 mm wide, 31 segments. Body colour in alcohol often tan to light brown, sometimes ashen or cinereous (Fig. 9A, C). Cuticular papillae evenly distributed over most of the body especially posteriorly, starting at segment 8. Single transverse dorsal rows of clusters of papillae per segment, especially towards posterior end. First seven segments usually much cleaner and translucent, especially in smaller individuals. Body up to 15 mm long, 8 mm wide, about 31 segments.

Prostomium hemispherical, opalescent, without eyespots, minutely granular in appearance. Peristomium rounded, without papillae, slightly raised near mouth. Mouth slightly oval, completely covered by papillae, extends from prostomium almost to edge of segment 2.

First three chaetigers with 6-12 bronze, widely separated, slightly falcate hooks per ramus, with subdistal dark areas, transparent in juveniles, opaque in larger specimens (Fig. 9C). Genital papillae protrude ventrally from intersegmental groove between segments 7 and 8. Pre-shield region with 7 segments, with small, short fascicles of fine capillary chaetae protruding laterally from body wall in some small specimens.

Ventro-caudal shield ribbed; juveniles with few concentric lines darker than the background shield colour, often covered by sediment (Fig. 9B), concentric bands better defined in larger specimens (Fig. 9D); suture extended throughout shield. Anterior margins rounded; anterior depression deep; anterior keels not exposed. Lateral margins straight in smaller specimens, curved in larger specimens, expanding posteriorly. Fan slightly projected beyond posterior corners, smooth in juveniles, crenulated in larger specimens, with a median shallow notch (Figs 1B, 9B).

Marginal chaetal fascicles include 10 lateral ones, chaetae in an oval arrangement, and 6-7 posterior fascicles, chaetae arranged in an approximately ventro-dorsal line. Lateral chaetae light bronze proximally along the shafts, grading to almost clear at the distal ends. Peg chaetae short, often obscured by adhered sediment or filamentous papillae among bases of chaetae. Additional short delicate capillary chaetae between peg chaetae and first posterior fascicle of shield chaetae.

Branchiae stout, coiled, protruding from two oval, obliquely set plates, one on either side of anus. Many long filamentous interbranchial papillae with sediment particles attached.

Variation.

The ventro-caudal shield is covered with sediment which is adhered to thin papillae in smaller specimens. Larger specimens have sediment particles less firmly adhered and can be brushed off. The pigmentation pattern is banded with concentric lines well-defined but ribs barely prominent; the fan is slightly projected and markedly cleft (Fig. 9 E–F, G), and the posterior margin is smooth in smaller specimens becoming slightly crenulated in larger specimens.

Remarks.

The taxonomic status of Sternaspis fossor Stimpson, 1853 requires clarification because it has been regarded as a widely distributed species, or has been taken either as a senior synonym of the Northwestern Pacific species, Sternaspis affinis Stimpson, 1864, or as junior synonym for the Mediterranean species, Sternaspis scutata (Ranzani, 1817). In order to clarify this situation, a neotype has been proposed together with the above description and illustrations ( ICZN 1999, Art. 75.3.1-75.3.3). As for Sternaspis affinis (see above), Stimpson’s original material was destroyed during the great Chicago fire in 1871. Despite the fact that the original description was brief, Sternaspis fossor is apparently the only species living in the type locality region, and we are confident that the neotype corresponds to the species ( ICZN 1999, Art. 75.3.5). The above proposed neotype was collected nearby the type locality, Grand Manan Channel ( ICZN 1999, Art. 75.3.6), although there were no details about depth or sediment type. The neotype has been deposited in National Museum of Natural History ( ICZN 1999, Art. 75.3.7).

Sternaspis fossor resembles Sternaspis affinis , Sternaspis islandica and Sternaspis maior because their shields are provided with rounded anterior margins, the lateral margins are slightly rounded, and the posterior margins are slightly expanded beyond the posterolateral corners. However, Sternaspis islandica differs by having a very shallow anterior depression, whereas the two other species have a deeper anterior depression. The three other species differ especially in the ornamentation of the shield surface because in Sternaspis fossor the radiating ribs and posterolateral corners are poorly developed, barely visible, whereas in Sternaspis affinis and Sternaspis maior they are often distinct.

Distribution.

Northwestern Atlantic Ocean, from Canada to the northeastern United States coast, in 20-153 m. Other records ( Augener 1906: 191, Wesenberg-Lund 1962: 142) need confirmation. The distribution of the true Sternaspis fossor is probably much less extensive than previously thought, and may be confined to the east coast of Canada and northeastern coast of the United States.