Sternaspis sendalli, Salazar-Vallejo, Sergio I., 2014

Salazar-Vallejo, Sergio I., 2014, Three new polar species of Sternaspis Otto, 1821 (Polychaeta: Sternaspidae), Zootaxa 3861 (4), pp. 333-344 : 339-342

Sternaspis sendalli n. sp.

Figs 4 , 5

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. Holotype. Scotia Sea. South Orkneys. Holotype ( BMNH 1930.10.8.2372–2400), and five paratypes ( BMNH 1930.10.8.2372–2400p), damaged (12.0– 12.5 mm long, 5–6 mm wide, abdomen 7.0– 8.3 mm long; left shield plate 1.3–2.8 mm long, 2.0– 2.2 mm wide).

Additional material. Scotia Sea. Palmer Archipelago. Two specimens ( BMNH 1930.10.8.2316), R.V. Discovery, Sta. 190, 315 m, 24 Mar. 1927 (largest specimen with abdomen depressed, shield broken; 10–12 mm long, 4.5–5.5 mm wide, abdomen 6–7 mm long; left shield plate 1.5–1.7 mm long, 1.8– 1.8 mm wide). Ten specimens ( BMNH 1930.10.8.2319–2340), R.V. Discovery, Sta. 181, 160– 335 m, 3 Dec. 1927 (juveniles; one specimen with pharynx fully everted, scoop-shaped; 5.5–8.0 mm long, 2–3 mm wide, abdomen 2.5–5.0 mm long; left shield plate 0.7–1.3 mm long, 0.8–1.4 mm wide; suture wide, posterior notch well defined, even in smaller specimens). Ten specimens ( BMNH 1930.10.8.2353–2370), R.V. Discovery, Sta. 182, 278– 500 m, 14 Mar. 1927 (juveniles; 3.0– 7.5 mm long, 1–2 mm wide, abdomen 2–4 mm long; left shield plate 0.5–1.1 mm long, 0.6–1.1 mm wide). South Georgia. Three specimens ( BMNH 1930.10.8.2224-2225), juveniles, R.V. Discovery, Sta. 144, 155– 178 m, 5 Jan. 1927 (body 6.0– 6.5 mm long, 2–3 mm wide, abdomen 3.0– 3.5 mm long; left shield plate 1.1 mm long, 1.1 mm wide). Six specimens ( BMNH 1930.10.8.2301-2303), body wall broken, one broken into two pieces, four with pharynx everted in different stages, R.V. Discovery, Sta. 45, 238– 270 m, 6 Apr. 1927 (6.3–7.0 mm long, 2.0– 2.8 mm wide, abdomen 3.8–4.8 mm long; left shield plate 1.2–1.3 mm long, 1.0– 1.1 mm wide; mature females with oocytes 150–200 µm). South Orkneys. Nine specimens ( BMNH 1930.10.8.2482–2488), R.V. Discovery, Sta. 162, 320 m, 17 Feb. 1927 (body 10.5–11.0 mm long, 4–5 mm wide, abdomen 6–7 mm long; left shield plate 1.8–2.1 mm long, 1.8–2.1 mm wide; some with oocytes, each 200 µm). Palmer Peninsula. Four specimens ( USNM 56109), RV Eltanin, Sta. 418 (62°39 S, 56°10 W), 311–426 m, 2 Jan. 1963 (1.5–4.8 mm long, 1.0–4.0 mm wide; left shield plate 0.5–1.5 mm long, 0.5–1.6 mm wide. Scotia Sea. One specimen ( USNM 56107), distorted by label, partially dehydrated, RV Eltanin, Sta. 340 (53°08 S, 59°31 W), 578– 567 m, 3 Dec. 1962 (3.8 mm long, 2 mm wide; ventral shield distorted, bent posteriorly). Weddell Sea. Six specimens ( USNM 56108), RV Eltanin, Sta. 416 (62º40' S, 56º13' W), 494–507 m, 2 Jan. 1963 (2.3–7.0 mm long, 1.0–4.0 mm wide, abdomen 1.5–5.5 mm long; left ventro-caudal shield plate 0.5–1.0 mm long, 0.5–1.5 mm wide). One specimen ( USNM 56111), RV Eltanin, Sta. 498 (61°40 S, 45°09 W), 366 m, 20 Feb. 1963 (4.3 mm long, 2 mm wide, abdomen 2.8 mm long; left shield plate 1.1 mm long, 1 mm wide). One specimen ( USNM 56112), distorted, markedly contracted, ventral shield detached, RV Eltanin, Sta. 500 (62°06 S, 45°12 W), 489–490 m, 21 Feb. 1963.

Description. Holotype (BMNH 1930.10.8.2372–2400) complete ( Fig. 4 A). Body pale, introvert fully exposed, slightly paler than abdomen, constriction or waist segments relaxed; ventro-caudal shield pale red. Introvert finely papillose, abdomen finely papillose. Body 15 mm long, 5 mm wide, abdomen 8 mm long; left ventro-caudal shield plate 2.5 mm long, 2.5 mm wide.

Prostomium hemispherical, projected, paler than surrounding areas. Eyespots not seen. Peristomium round, with scarce papillae extended laterally over prostomium and ventrally to margin of first chaetiger.

Introvert chaetigers with 12–14 brassy falcate hooks, each with subdistal darker areas, tips mucronate ( Fig. 4 B). Genital papillae small, short, digitate, with same pigmentation than 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 and barely defined concentric lines ( Fig. 4 A, C). Anterior margins rounded; anterior depression shallow. Suture visible throughout shield. Lateral margins rounded, expanding posteriorly, smooth. Fan slightly projected beyond posterior corners level, notched medially, and with lateral notches, margin barely crenulated.

Marginal chaetal fascicles slightly damaged, mostly complete but some chaetae broken, 9 lateral ones, and 5–6 posterior fascicles, all chaetae arranged in oblique rows. Peg chaetae mostly lost, some remaining towards the right posterior corner.

Branchiae abundant, very thin and long, coiled, most lost; interbranchial papillae long, curled, often with fine sediment particles. Branchial plates bordering anal peduncle, anteriorly tapered to a blunt tip. One mature female (BMNH 1930.10.8.2301-2303, BMNH 1930.10.8.2482–2488) with oocytes 150–200 µm.

Variation. Ventro-caudal shield varies in pigmentation and on the relative fan’s ventral projection. It is usually orange in small specimens becoming darker or reddish in larger ones. Marginal chaetal fascicles were 9 lateral and 5-6 posteriorly. The suture is wide and the posterior notch well defined, even in smaller specimens. The fan varies regarding its projection; most have it distinct but some smaller specimens have it less pronounced. Fan is always notched medially and laterally; its margin is smooth only in very small specimens, becoming slightly crenulated with increasing body size. Adult or larger specimens have a thick integument layer over shield, more or less removable by brushing. Others with shields with wide suture, deep median notch, and posterior corners more pronounced than in small specimens. Additional material varied from 1.5–12.5 mm in length and 1–6 mm in width; left shield plate 0.5–2.8 mm long, 0.5–2.2 mm wide.

Etymology. This species is named after Kelly Sendall, in recognition of his studies on sternaspids, and because of his enthusiastic support of my research activities. The epithet is a noun in the genitive case.

Remarks. Sternaspis sendalli n. sp. resembles the Mediterranean S. scutata ( Ranzani, 1817) , and this explains why it has previously been confused ( Monro 1930, Augener 1932, Hartman 1953, 1966, 1967), because both have shields with fans projected with median and lateral notches. However, in S. sendalli n. sp. the shield is orange, its anterior depression is shallow or very shallow, the lateral margins are more markedly expanded laterally, and the fan is more projected with larger lateral notches. In contrast, the shields in S. scutata are reddish, their anterior depressions are deep, with their lateral margins less expanded laterally, and with shorter fans with shallower lateral notches.

On the other hand, S. sendalli n. sp. resembles S. costata von Marenzeller, 1879 from Japan because both species have shields with a distinct, deep median notch, ribs and concentric lines well developed, and their posterolateral corners are distinct in frontal view. These species differ because of the relative distinctness of ribs and concentric lines, and body colour; in S. sendalli n. sp. radial ribs and concentric lines are barely defined, and the body is brownish, whereas S. costata has ribs and concentric lines distinct, and with body whitish to grayish.

Distribution. Antarctic Ocean: Palmer Peninsula and Archipelago, South Georgia, South Orkneys, South Shetland Islands, Weddell Sea, in 160– 567 m.

Figures

FIGURE 1. Sternaspis buzhinskajae n. sp., holotype (CAS 9853). A. Complete specimen, ventral view (arrow points to genital papilla), B. Frontal view of anterior end, C. Close-up of ventro-caudal shield. Scale bars. A: 1.5 mm, B: 1.1 mm, C: 0.8 mm.

FIGURE 4. Sternaspis sendalli n. sp. A – C. Holotype (BMNH 1930.10.8.2372 – 2400), A. Complete specimen, ventral view, B. Anterior end, left side view, C. Same, ventro-caudal shield, frontal view, D – F. Smaller paratype (BMNH 1930.10.8.2372 – 2400 p), D. Ventro-caudal shield, frontal view, smaller one, E. Ventro-caudal shield, frontal view, medium one, F. Ventro-caudal shield, larger one. Scale bars. A: 1.7 mm, B, E: 1.1 mm, C: 0.8 mm, D: 0.9 mm, F: 1.2 mm.

FIGURE 5. Sternaspis sendalli n. sp., several juvenile specimens (USNM 56108), A. Smallest, ventral view, B. Two slightly larger specimens, ventral view, C. Ventro-caudal shield, frontal view, smaller specimen in B, D. Ventro-caudal shield, frontal view, larger specimen in B, E. Largest specimen, ventral view, F. Same, introvert hooks partly exposed, G. Same, ventro-caudal shield, frontal view. Scale bars. A: 0.7 mm, B: 1.3 mm, C: 0.2 mm, D: 0.4 mm, E: 1.7 mm, F: 0.3 mm, G: 0.5 mm.