Styela changa Monniot & Andrade, 1983

Turon, Xavier, Cañete, Juan I., Sellanes, Javier, Rocha, Rosana M. & López-Legentil, Susanna, 2016, Ascidian fauna (Tunicata, Ascidiacea) of subantarctic and temperate regions of Chile, Zootaxa 4093 (2), pp. 151-180 : 172

Styela changa Monniot & Andrade, 1983

Fig. 13 A–C

References and synonymy: Styela changa Monniot & Andrade (1983) p. 134; Millar (1988) p. 233.

Localities: 4N, 5N.

The body is globular or dorso-ventrally flattened, up to 12 mm in maximal dimension, fixed by the ventral side. The tunic is tough, brownish, and with tubercles and wrinkles. The mantle wall is very thin, particularly in the ventral region. It is very hard to extract an unbroken individual from the tunic.

Oral tentacles are simple, up to 30. The aperture of the neural gland is in the shape of a vertical slit and the dorsal lamina is smooth and low. There is an atrial velum with a circle of filiform tentacles extending anteriorly in a double row. The branchial sac has 4 folds on each side, with up to 8 stigmata per mesh, often crossed by parastigmatic vessels.

The digestive system is distinctive. It is formed by a cylindrical stomach with folds, and a prominent hepatic gland formed by branched diverticula that originate from two main stems in the anterior part of the stomach and smaller ones located more posteriorly. The pyloric end of the stomach has a well-developed and coiled caecum. The isodiametric intestine forms a primary loop that can be more or less closed depending on the individual. The intestine is not flat against the mantle wall. Rather, it is quite unattached and is twisted in three dimensions. The secondary loop is little marked, except for a final bend of the rectum.

There are two gonads per side, each formed by an elongated and convoluted ovary and, ventrally, ramified male follicles. The male and female openings are close together at the distal end. The gonads, and particularly the male follicles, are unattached and become easily separated from the mantle. The posterior left gonad is partially under the intestine. Small endocarps are present at both sides.

Remarks. this species was described from Chile, off Coquimbo at 450 m depth (Monniot & Andrade 1983), and was later reported from the northern coast of Peru (05º S) between 200 and 300 m (Millar 1988). We have found it at ca. 100 m depth, thus enlarging its known bathymetric range. This is the third finding of this species, well characterized by its hepatic gland, of unique morphology among the Styelidae .

Figures

FIGURE 13. Styela changa. A, whole individual; B, C, dissected digestive system as seen from the branchial side (B) and from the mantle side (C); D, Specimens of Styela paessleri partially overgrown by Didemnum studeri; E, dissected mantle of an immature individual, branchial sac removed (stained material); F, anterior part of a larva. Scale bars: A, 2 mm, B, C, 0.5 mm, D, E, 1 cm, F, 50 µm.