Sternaspis uschakovi, 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 : 15-18

Sternaspis uschakovi sp. n. Figures 7, 8

Sternaspis scutata : Uschakov 1950: 215, 1953: 154 (distr., non Ranzani 1817, partim).

Sternaspis fossor : Fauchald 1972: 238-239 (partim, non Stimpson 1853); Méndez 2007: 609, 613-616 (lists) (partim, non Stimpson 1853).

Type material.

Northwestern Pacific Ocean. Holotype (ZIRAS 50604) and 15 paratypes (ZIRAS 50605), Okhotsk Sea, R.V. Gagara, Sta. 251 (55°13'N, 146°52'E), 592 m, 12 Sep. 1932 (four complete paratypes exposing their introvert 5-8 mm long, 4.0-5.5 mm wide, abdomen 3.5-5.0 mm long, left ventro-caudal shield plate 1.0-1.6 mm long, 1.5-2.0 mm wide).

Additional material.

Northwestern Pacific Ocean. 12 specimens (ZIRAS 50606) Okhotsk Sea, R.V. Gagara, Sta. 215 (49°25'N, 152°00'E), 1366 m, 8 Aug. 1932 (10 specimens with exposed introvert 10.0-13.0 mm long,4.0 mm wide (waist), abdomen 4.0-5.5 mm long, left ventro-caudal shield plate 2.0-2.5 mm long, 2.0-2.8 mm wide). Three specimens (ZIRAS 50607) juveniles, Okhotsk Sea, R.V. Gagara, Sta. 214 (49°23'N, 148°46'E), 1076 m, 6 Aug. 1932 (juveniles with a very thin shield; abdomen 4.5 mm long, one with introvert partially exposed 7 mm long). Northeastern Pacific Ocean. Oregon. Three specimens (CAS 149923) previously dried out, BMT-554 (47°49.9'N, 127°2.9'W), 2510 m, 8 Sep. 1971, A. Carey, coll. (8.0-10.5 mm long, 3-5 mm wide; left shield plate 2.2-2.5 mm long, 2.9-3.0 mm wide). California. Nine specimens (SIORAS 4214), R.V. Vityaz, Cruise 29, Sta. 4214 (35°01.5'N, 121°42.5'W), 1585 m, 6 Dec. 1958 (best preserved specimen 12 mm long, 3.4 mm wide (waist), abdomen 8.6 mm long). Gulf of California. One specimen (UNAM 7879), introvert broken, off Ensenada del Pabellón, Sinaloa, RV El Puma, Cruise Talud IV, Sta. 19 (24°15'18"N, 108°24'06"W), 1245 m, 25 Aug. 2000 (5 mm long, abdomen 2.8 mm wide; ventro-caudal shield reddish, bent dorsally, wider than abdomen; fan projected medially, posterior margin dentate, last lateral chaetal bundles about 3 mm long). One specimen (UNAM 7880), introvert broken, RV El Puma, Cruise Talud IV, Sta. 26 (24°56'24"N, 109°05'36"W), 1200-1274 m, 26 Aug. 2000 (5.5 mm long, abdomen 2 mm wide; ventro-caudal shield broken, reddish, bent dorsally, wider than abdomen; fan projected medially, posterior margin dentate; last lateral chaetal bundles about 3 mm long). Three specimens (UNAM 7884), two complete, introvert exposed; off Lechugilla Island, Sinaloa, RV El Puma, Cruise Talud IV, Sta. 34 (25°43'50"N, 109°53'59"W), 1240-1270 m, 17 Mar. 2001 (6.3-11.0 mm long, abdomen 3.0-4.5 mm wide; ventro-caudal shield reddish, bent dorsally, wider than abdomen in one specimen; fan projected medially, posterior margin dentate; last lateral chaetal bundles about 3.5 mm long). Western Mexico. Eight specimens (LACM 5347), juveniles, most with introvert invaginated or damaged, some with body wall broken, S off Cabo Corrientes, Jalisco, R.V. Velero IV, Sta. 13755 (19°51'30"N, 105 °50'00"W), 2548 m, mud, Campbell grab, 18 Jan. 1970 (4.0-5.0 mm long, 2.0 mm wide; left shield plate 0.8-1.3 mm long, 1.5-1.8 mm wide).

Description.

Holotype (ZIRAS 50604) with body anteriorly swollen, slightly darker than posterior region; introvert fully exposed, pale, abdomen creamy (Fig. 7A), ventro-caudal shield dirty reddish, with orange central areas (Fig. 7B, D). Body 14 mm long, 5 mm wide (mid body constriction), abdomen 9 mm long, left ventro-caudal shield plate 2.2 mm long, 2.7 mm wide. Introvert mostly smooth, barely papillose, abdomen papillae mostly eroded, some retained in folds or around branchial region.

Prostomium hemispherical (Fig. 7C); projected, with same pigmentation as introvert. Eyespots not seen. Peristomium round with abundant papillae restricted to peripheral areas around the mouth, barely reaching margin of first chaetiger.

Introvert chaetigers with 9-11 golden, barely falcate hooks, each with subdistal dark areas but tips mostly eroded (Fig. 7C). Genital papillae small, thin, blunt, with same pigmentation than introvert, in intersegmental groove between segments 7 and 8.

Anterior abdomen with 7 segments, lateral lobes well-defined by contraction, dorsal area bare, converging posteriorly, ventral area bare, more or less parallel; papil lae mostly eroded, some remaining in branchial region, but not arranged in series or groups. Capillaries not seen.

Ventro-caudal shield with lateral plates slightly bent dorsally, making them look quadrate in frontal view (Fig. 7D) but each plate wider than long (Fig. 7B); suture visible throughout shield. Ribs barely developed, concentric lines poorly developed but present. Anterior margins barely rounded, midventral depression shallow. Lateral margins gently rounded, expanded posteriorly. Fan projected medially beyond posterior corners, margin denticulate.

Marginal chaetal fascicles mostly broken off (Fig. 7A, B, D), 9 lateral ones with chaetae along an oblique series, and 6 posterior fascicles with chaetae in linear arrangement. Peg chaetae not visible (some paratypes have them).

Branchiae still attached, abundant, spirally bent filaments; interbranchial papillae long, spirally bent, with fine sediment particles. Branchial plates observed in some paratypes, wide, progressively wider towards anterior margin, with 7-8 filaments per series.

Etymology.

This species is being named after the late Dr. Pavel V. Uschakov as a modest homage to his monographic publications, especially those regarding the Okhotsk Sea fauna, and by his other numerous publications on polychaetes. The epithet is a noun in the genitive case.

Variation.

The introvert is markedly swollen, like in the holotype, in one paratype and in some non-type specimens. Introvert chaetigers with 9-10 hooks per bundle. The ventro-caudal shield is dirty orange to pale brick red, ribs and concentric lines are always visible but variably developed; anterior margins rounded to barely acute (Fig. 7 E–G); fan markedly projected medially, with shallow lateral notches, margin denticulate rarely reaching the level of the posterior corners. The inner margins of each lateral shield plate are fused along most of its length. The shield chaetal bundles are difficult to count but there are 9 lateral and 7 posterior bundles in better preserved paratypes. On the other hand, the specimens from the Northeastern Pacific have bodies with larger, more abundant papillae (Fig. 8A), and they are also evident in the mouth region (Fig. 8B); the ventro-caudal shield (Fig. 8C), however, is very similar to the specimens from the Northwestern Pacific. We regard the apparent difference in integument papillation as a result of different sampling and sorting procedures and not as a significant, diagnostic difference. Therefore, we conclude they are conspecifics.

Remarks.

Sternaspis uschakovi sp. n. differs from other deep-sea Sternaspis species because its ventro-caudal shield is medially projected, but resembles two other species having a ventro-caudal shield with denticulated posterior margin: Sternaspis africana Augener, 1918, and Sternaspis andamanensis Sendall & Salazar-Vallejo, 2013. However, these two species have been found in shallow water (5-70 m), whereas Sternaspis uschakovi was found in water depths of 592-2548 m. There are two other differences when this new species is compared to the other two; first, the midventral depression is shallow in the new species, resembling Sternaspis africana , whereas it is deep in Sternaspis andamensis ; and second, the fan posterior margin has two lateral deep notches in Sternaspis andamanensis whereas in Sternaspis uschakovi and in Sternaspis africana the fan is not so markedly notched laterally. Further, as indicated in the key below, Sternaspis uschakovi is more similar to Sternaspis andamanensis but they can be easily separated because in Sternaspis uschakovi there are about 10 dark introvert hooks per bundle, whereas in Sternaspis andamanensis there are about 15 pale introvert hooks per bundle.

Distribution.

Okhotsk Sea in 592-1366 m, California in 1585 m, Gulf of California in 1200-1274 m, and off Western Mexico in 2548 m, in mud or muddy sands.