Sternaspis monroi Salazar-Vallejo, 2014, n. sp.

Sternaspis monroi n. sp.

Fig. 3

Sternaspis scutata: Monro, 1930: 178 –179; Augener, 1932: 56; Hartman, 1953: 10; 1966: 55, Pl. 18, Fig. 1; 1967: 141 (partim, non Ranzani, 1817).

Type material. Scotia Sea. South Orkneys. Holotype (BMNH 1930.10.8.2372–2400R), and three paratypes (BMNH 1930.10.8.2372–2400 Rp), R.V. Discovery, Sta. 167, 244– 344 m, 20 Feb. 1927 (paratypes 11–15 mm long, 5–6 mm wide, abdomen 7–8 mm long; left ventro-caudal shield plate 2.0– 2.5 mm long, 2.2–2.6 mm wide).

Additional material. Scotia Sea. South Orkneys. Three specimens (BMNH 1930.10.8.2482–2488R), R.V. Discovery, Sta. 162, 320 m, 17 Feb. 1927 (14 mm long, 5.0– 5.5 mm wide, abdomen 8 mm long; left shield plate 2.1– 2.2 mm long, 2.3–2.4 mm wide). South Georgia. Two specimens (BMNH 1930.10.8.2301-2303R), body wall well-preserved, pharynx not exposed, R.V. Discovery, Sta. 45, 238– 270 m, 6 Apr. 1927 (shields without concentric lines, banded, one with a deep median notch belongs to S. sendalli n. sp., see below, 7 mm long, 3 mm wide, abdomen 4 mm long).

Description. Holotype (BMNH 1930.10.8.2372–2400R) complete (Fig. 3 A). Body pale, introvert fully exposed, with similar pigmentation as abdomen, constriction or waist segments relaxed; ventro-caudal shield brick red with paler submarginal band (Fig. 3 A, B). Introvert mostly smooth, abdomen finely papillose. Body 14 mm long, 4.8 mm wide, abdomen 7 mm long; left ventro-caudal shield plate 2.1 mm long, 2.5 mm wide.

Prostomium hemispherical, projected, whitish. Eyespots not seen. Peristomium round, slightly damaged, with few papillae, barely extended laterally and ventrally to margin of first chaetiger.

Introvert chaetigers with 12–14 brassy, falcate hooks, each with subdistal darker areas, tips mucronate (Fig. 3 A, C, E). Genital papillae small, short, digitate, with same pigmentation as introvert, visible in intersegmental area between segments 7 and 8. Anterior abdomen with 7 segments, papillae evenly distributed, not arranged in series or groups. Capillaries not seen.

Ventro-caudal shield surface with ribs, concentric lines not visible (Fig. 3 B, D). Anterior margins rounded, anterior depression shallow. Suture visible throughout shield. Lateral margins rounded, expanded posteriorly, smooth. Fan truncate, not projecting beyond posterior corners level, median notch narrow, short, without lateral notches, margin markedly crenulated.

Marginal chaetal fascicles slightly damaged, mostly complete but some chaetae broken, 9 lateral ones, and 6 posterior fascicles all with chaetae arranged in oblique rows. Peg chaetae mostly lost, a few remaining towards posterior corners.

Branchiae abundant, very thin, long, coiled, most lost; interbranchial papillae long, curled, often with fine sediment particles. Branchial plates bordering anal peduncle, anteriorly expanded, rounded.

Variation. Larger specimens with shields with fan truncate, median notch indistinct. In two specimens (Fig. 3 F, G), the posterior margin is denticulate, and in one of them (Fig. 3 F) even the anterior margin is very different from the typical shield shape. Body was 7–15 mm long, 3–6 mm wide; left shield plate 2.0– 2.5 mm long, 2.2–2.6 mm wide

Etymology. This species name is to honor C.C.A. Monro, in recognition of his many publications of polychaetes, and especially because he studied the specimens included in this description, and these were the first record of sternaspids from Antarctic waters. The epithet is a noun in the genitive case.

Remarks. Sternaspis monroi n. sp. resembles S. princeps Selenka, 1885 from New Zealand because both have shields with continuous fans, with margin crenulated, not projecting posteriorly, and although ribs are distinct, concentric lines are hardly visible. These two species differ in the relative shape of each plate and in the distinctness of larger, diagonal ribs; in S. monroi n. sp. plates are wider than long and diagonal rib is indistinct, whereas in S. princeps plates are as long as wide, and diagonal rib is distinct. Two specimens with some modifications on their shield outline, having markedly reduced anterior margin or with denticulate posterior margins and a rather thin shield, are regarded as ontogenetic aberrations and not intraspecific variation, and are not included in the paratype series.

Distribution. South Orkneys and South Georgia islands, in 238–344 m depth.