Ascidia cf. munda Sluiter, 1897

Bonnet, Nadia Y. K. & Rocha, Rosana M., 2011, The family Ascidiidae Herdman (Tunicata: Ascidiacea) in Bocas del Toro, Panama. Description of six new species, Zootaxa 2864, pp. 1-33 : 19-21

Ascidia cf. munda Sluiter, 1897

( Fig. 12 )

Material examined. DZUP ASC 158—1 ind.; Garden; 7.0 m; coral reef; 10.viii.2008.

The only animal found was attached by its left side to a dead coral fragment on the sea bottom. The tunic is smooth with a few round projections connected by a thin stalk; it is thin and completely transparent. The body is elongate, oval, slightly flat on both sides, 3.6 cm long (including the oral siphon) by 1.4 cm, without tunic. The oral siphon is 0.5 cm long, the atrial siphon is 0.8 cm and displaced towards the oral siphon. Eight triangular lobes are on the oral siphon and 10 on the atrial, both with projections at the margins, and a yellow spot between the lobes. Siphons are lined by a delicate membrane which has small papillae on the posterior half of the oral siphon.

The body wall is colorless. On the right side, the body wall musculature is complex, comprising bands of parallel fibers along the dorsal and ventral margins; the dorsal band is larger posteriorly. There are also very few and thin longitudinal fibers in the anterior margin. On the left side, short transverse fibers are along the dorsal line. Musculature in the siphons is weak, but both siphons have circular and longitudinal musculature (not concentrated in bands).

The 80 oral tentacles are of three sizes, the largest is 2.5 mm long, thick along most of its length and slender at the tip. The tentacles project from a conspicuous but thin muscular ring. The peripharyngeal groove is double, the anterior lamina has long filiform projections; the line of tentacles is separated from the prepharyngeal groove by 0.7 mm, in which area are several large papillae. The peritubercular area is U-shaped; the dorsal tubercle aperture is U-shaped with enrolled ends. The neural ganglion is displaced toward the oral siphon, close to the dorsal tubercle. The dorsal lamina is double anteriorly and with small finger like projections formed by the ends of the left transverse vessels and additional small projections between them; there are also small papillae on the right side of the dorsal lamina before the esophageal aperture. The dorsal lamina is equally wide in all the extension and passes by the esophageal aperture on its left to the end of the pharynx, which extends beyond the stomach. The pharynx has 47 longitudinal vessels on the right, 40 on the left and 124 transverse vessels; it is not pleated and meshes have 5–7 stigmata. The primary papillae comprise one or two large lobes with a lateral expansion on each side; the lobes are long and have a large base connecting to the transverse vessels; pharynx lacks intermediate papillae. The parastigmatic vessels are very rare and when found are usually associated with incomplete transverse vessels.

The alimentary canal is large, occupying half of the left side of the body. The stomach is tubular and narrow, with few (~ 6) internal folds. The intestine forms two loops and the descending portion is dilated forming a sac-like pouch. The anus is located about 7.2 mm from the oral tentacles, is large and has an undulated rim. Large papillae cover the stomach wall and ascending portion of the intestine on the atrial side.

The cauliflower-shaped ovary is restricted to the extremity of the primary intestinal loop and best seen from the outside. The oviduct opens by a large slit on the same level of the anal aperture. The testis comprises large, oval or pyriform follicles, spread mainly on the descending intestine and base of the rectum, and almost not visible from the outside. The sperm duct aperture is beside the female aperture but smaller.

Remarks. Because of the external vesicles on the tunic, this species can be confused with A. interrupta . But, in A. munda the vesicles attached by a thin stalk, the body wall is colorless, the muscular pattern is different on the right side and fewer lobes are on the oral siphon.

Ascidia munda is known from the Pacific Ocean ( Kott 1985; Monniot 1987; Monniot 1990). The sample described here is very similar to specimens from New Caledonia ( Monniot 1987), differing by the projections at the border of the siphon lobes and the non-ramified ovary. According to Kott (1985), Australian specimens have projections in the siphons lobes, individuals can reach up to 8.0 cm total length, they have an irregular dorsal tubercle and up to 10 stigmata per mesh in the pharynx (no description of the ovary). Due to this variation, we decided to identify the present material as A. munda , probably with an incompletely developed ovary.

Figures

FIGURE 12. Ascidia cf. munda Sluiter, 1897. A. Animal in the field. B. Dorsal tubercle and anterior part of the dorsal lamina. C. Gut and gonads (internal). D. Right side of body (external), showing muscles. E. Left side of body (external), showing the gut and gonads. Scale bar: B = 1.0 mm; C, D, E = 0.5 cm.