Styela squamosa Herdman 1881

Styela squamosa Herdman, 1881

References and synonymy: Styela squamosa Herdman 1881: 66; Sanamyan & Sanamyan 2006: 321, figs. 7–9 (synonymy); 2012: 67, fig. 3.

Material examined: One individual; trawl; -37.9651 lat. -54.5320 long. (station 10); 1144 m; 11 August 2012 (Figure 12).

The specimen measures 1.9 cm high and 1.2 cm wide. It was found completely covered by a thick and tough layer of sediment, with rests of sand and pebbles (Fig. 12). There are 18 oral tentacles disposed on the margin of an oral velum. The muscle fibers are densely packed and equally distributed on both sides. The branchial sac has four well developed folds on each side. Thin parastigmatic vessels are present. The stomach presents 24 well-marked folds and bears a small straight pyloric caecum. The border of the anus is triangular and ends near the atrial opening. There is one sinuously curved gonad on each side. The ovary is long and narrow. The small testicular follicles are placed around the distal part of each ovary. Numerous endocarps are distributed on both sides of the body.

Remarks. Styela squamosa has been described from most ocean basins in the world, except from the North Atlantic and Indian Oceans, at depths ranging from 165 to 5000 m. This data permits to classify S. squamosa as an eurybathic and cosmopolitan deep-sea species (Monniot C. 1993). There is, though, some degree of character variation that falls into the range of standard intra-specific variability. Our specimen encountered off La Plata River (SW Atlantic), is closest to the description made by Sanamyan (1992) of a few individuals from the Sea of Okhotsk (NW Pacific) in relation to the shape of the border of the anus. While previous descriptions state that the border of the anus is bilobed, Sanamyan´s specimens as well as ours, present a triangular border. The only difference between our specimen and all the rest resides in the number of oral tentacles: 18 in ours and around 30 in the rest.