Sternaspis annenkovae, Salazar-Vallejo, Sergio I. & Buzhinskaja, Galina, 2013

Salazar-Vallejo, Sergio I. & Buzhinskaja, Galina, 2013, Six new deep-water sternaspid species (Annelida, Sternaspidae) from the Pacific Ocean, ZooKeys 348, pp. 1-27 : 8-10

Sternaspis annenkovae sp. n. Figure 4

Sternaspis scutata : Levenstein 1961: 167, 1966: 59 (non Ranzani 1817, partim)

Type material.

Northwestern Pacific Ocean. Holotype (ZIRAS 50602) and 11 paratypes (ZIRAS 50603), variably damaged, most with broken body wall and some broken by half, R.V. Vityaz, Sta. 2209 (49°46'01"N, 157°48'06"E), 3980-4070 m, grab Ocean, 1953 (five paratypes with introvert variably exposed and damaged, 6.0-11.0 mm long, 4.0-6.0 mm wide, ventral shield left plate 2.0-2.8 mm long, 2.1-3.0 mm wide; oocytes yellowish, still in ovary, about 200 µm; paratypes without introvert but abdomen well preserved, 6-12 mm long, 4.0-8.0 mm wide, ventral shield left plate 2.0-2.8 mm long, 2.3-3.5 mm wide; oocytes in ovary about 200 µm).

Description.

Holotype (ZIRAS 50602) with body bi-colored; introvert not fully exposed, pale brown, abdomen whitish (Fig. 4A), ventro-caudal shield pale brick red (Fig. 4B, D). Introvert finely papillose, abdomen papillae mostly eroded, some retained in folds or around branchial region. Body 10 mm long, 7 mm wide, abdomen 8 mm long, left ventro-caudal shield plate 2.0 mm long, 2.7 mm wide.

Prostomium hemispherical (Fig. 4C), (similar in paratypes; slightly acute in one paratype), projected, slightly larger than mouth, with same pigmentation as introvert. Eyespots not seen. Peristomium rounded with abundant papillae, extended laterally over prostomium and ventrally to margin of first chaetiger.

Introvert chaetigers with 10-11 golden barely falcate hooks, each with subdistal dark areas but tips mostly eroded (Fig. 4C). Genital papillae small, digitate, with same pigmentation than introvert, barely visible in intersegmental groove between segments 7 and 8.

Anterior abdomen with 7 segments, papillae mostly eroded, some remaining in body depressions or around branchial region, but not arranged in series or groups. Capillaries not seen (two paratypes with capillaries in first two segments, two per bundle).

Ventro-caudal shield with lateral plates divergent, surface with ribs and concentric lines, the latter less pronounced, barely banded; suture visible throughout shield. Anterior margins rounded, midventral depression shallow (Fig. 4C). Lateral margins gently rounded, not expanded posteriorly. Fan markedly notched, barely projected beyond poorly developed posterior corners, margin barely crenulated.

Marginal chaetal fascicles mostly broken off (Fig. 4B, C), 10 lateral ones with chaetae along an oblique series, and 7 posterior fascicles with chaetae in linear arrangement. Peg chaetae not visible.

Branchiae mostly lost (few remaining in paratypes, spirally bent); interbranchial papillae long, straight, often with fine sediment particles. Branchial plates observed in some paratypes, narrow, anteriorly rounded, wider than rest of branchial plate, with 8-9 filaments per series.

Etymology.

This species name is after the late Dr. Nadezhda P. Annenkova, in recognition of her many publications on polychaetes, and for her efforts to build a strong taxonomic tradition in the early to mid XX century in Russia. The epithet is a noun in the genitive case.

Variation.

The introvert is always pale brown, darker than the abdomen. Introvert chaetigers have 11-13 hooks per bundle. The ventro-caudal shield is pale brick red or dirty orange, ribs and concentric lines are always visible but variably developed; anterior margins are rounded to barely acute (Fig. 4 E–G); fan markedly notched, margin barely crenulated to markedly crenulated, barely projected beyond the posterior corners. The inner margins of each lateral shield plate are fused along 1/2 to 1/3 of its length, resulting in a divergent or markedly notched fan. The shield chaetal bundles are difficult to count in holotype; paratypes with 9 lateral, and 6-7 posterior bundles.

Remarks.

Sternaspis annenkovae sp. n. is unique among the species in the genus and two features separate it. First, the body is bi-colored having a darker introvert and a pale abdomen, whereas in all other species the introvert is usually of the same color than the abdomen, slightly paler or even transparent. It is true that sometimes the sediment-filled gut can be displaced towards the introvert, making it look darker than the posterior region, but this can be noticed by transparency of the introvert’s body wall, whereas in Sternaspis annenkovae the pigmentation is widespread and homogeneous in the introvert. Second, the lateral shield plates are divergent and separated throughout its posterior region such that the fan is markedly notched. Some Sternapsis species can have a more eroded shield in older specimens, whereas the younger specimens are less eroded; however, in Sternaspis annenkovae the markedly notched fan is evident even in small specimens, rendering it a consistent feature, not significantly modified during growth. The other three deep-water species ( Sternaspis maior , Sternaspis princeps , and Sternaspis rietschi ) do not have a median notch or, if present, as in Sternaspis maior , it is rather shallow. Further, there are two species that have shields with deeply notched fans, especially in larger specimens as shown elsewhere ( Sendall and Salazar-Vallejo 2013): Sternaspis costata von Marenzeller, 1879 and Sternaspis islandica Malmgren, 1867. These species differ by having a wider fan such that the larger ribs form an angle of 100-120° whereas in Sternaspis annenkovae the fan is narrower and the larger ribs form an angle of 85-90°. However, as indicated in the key below Sternaspis annenkovae resembles Sternaspis fossor Stimpson, 1853 because their shields have radial ribs and concentric lines, fans with a deep, median notch, and poorly defined posterior corners. They differ because in Sternaspis annenkovae the introvert is darker than the rest of the body and its shield is wider anteriorly, whereas in Sternaspis fossor the introvert is paler or with similar pigmentation than the rest of the body, and the shield is wider medially.

On the other hand, Sternaspis annenkovae resembles Sternaspis williamsae sp. n. (described below) because in the ventro-caudal shields of both species the fan is narrower than the corresponding anterior margins. They differ because in Sternaspis annenkovae concentric lines are better developed, the fan is medially discontinuous, and the prostomium is larger than the mouth, whereas in Sternaspis williamsae the concentric lines are poorly developed, the fan is medially continuous, and the prostomium is smaller than the mouth.

Distribution.

Only known from the type locality in the Northwestern Pacific Ocean, east off northern Kurile Islands, in 3980-4070 m depth. Levenstein (1961, 1966) deep water records from the Bering Sea could belong to this species but her materials were not found.