Distaplia naufragii, Lagger, Cristian & Tatián, Marcos, 2013

Lagger, Cristian & Tatián, Marcos, 2013, Two new species of Distaplia (Tunicata: Ascidiacea) from the SW Atlantic, Argentina, Zootaxa 3620 (2), pp. 192-200 : 194-196

Distaplia naufragii sp. nov.

( Figures 2A , B, C; 3A, B)

Material examined. Las Grutas (Río Negro), Argentina. Holotype: MZUC T00005, one colony ( Fig. 2 B) sampled on 30/X/2011 at 20 m depth from the shipwreck “Don Félix” (40° 51.784 S; 65° 0 3.802 W). Paratypes: MZUC T00006, six colonies: 40° 51.784 S; 65° 0 3.802 W; 30/X/2011, 20 m.

Etymology. From naufragii , the genitive of the latin noun naufragium (= shipwreck).

Description. Small colonies consist of several mushroom-shaped lobes joined by short yellowish peduncles. Large colonies are composed of a cushion shaped lobe, which may reach 6.5 cm long by 4.5 cm high, attached to the substratum by a pale yellow small area. The basal portions of the colonies are burgundy colour while the upper layer of the tunic is semi-transparent allowing the observation of white pigment granules on the oral siphons of each zooid. The test is soft and free of epibionts. The zooids are perpendicular to the colony surface and organized in circular or elongated systems containing up to 25 zooids which converge into common cloacal aperture. The thoraces of the zooids are prominent and located in the uppermost layer of the tunic. Living colonies are easily recognizable underwater by the contrast between of burgundy basal area of the tunic and the white prominent zooids ( Fig. 2A ).

The zooids are large, reaching 5 mm or more in length when well expanded. The oral siphon, surrounded by abundant circular muscles, is smooth-edged or forming six sinuate lobes. The atrial aperture is wide, exposing much of the pharynx, and has a dorsal languet with plain edge.

The thorax bears about 40 thin oblique muscles (many of these are branched) on each side, most of which are concentrated around the opening of the atrial aperture. There are 15 to 21 thread-like oral tentacles of two sizes, arranged regularly in a single circle. The dorsal tubercle is small and circular, with an aperture of similar form. The four rows of long stigmata are crossed by well-developed parastigmatic vessels. There are about 18 to 21 stigmata in each half row. Three dorsal languets are displaced to the left side of the thoracic midline.

The slightly curved oesophagus connects to the stomach laterally. The oval stomach has conspicuous internal longitudinal ridges. Ridges are often curved, somewhat irregular or interrupted, giving a stretch-marked external appearance to the stomach wall. A pyloric gland extends between the stomach and the intestine. The intestine has a constriction situated at a short distance beyond the stomach. The bi-lobed anus opens at the level of the third row of stigmata.

The zooids are hermaphroditic. Gonads occupy the right side of the gut loop and consist of 8 to 15 male follicles and an ovary containing 7 to 9 oocytes of different sizes (one or two of them are large), situated mainly below the testis. The fine vas deferens ends at the same level as the anus.

The brood pouch projecting from the thorax, at the level of the fourth stigmata row, contains up to 6 developing larvae. The oval larval trunk may be up to 1.4 mm long. The larvae possess three adhesive papillae triangularly arranged; ampullae and epidermal vesicles were not observed. The tail is on the same level of the adhesive papillae and involves half or less of the larva. Each sensory vesicle contains both an otolith and an ocellus.

Figures

FIGURE 2. A, Distaplia naufragii sp. nov. at the shipwreck “ Don Félix ” (photo by R. Sahade). B, Large colony. C, Small colonies. D, Colony of Distaplia fortuita sp. nov. Scales: 2 cm.