Rhopalaea idoneta, Shenkar, Noa, 2013

Shenkar, Noa, 2013, A new species of the genus Rhopalaea (Class: Ascidiacea) from the Red Sea, Zootaxa 3599 (1), pp. 51-58 : 53-56

Rhopalaea idoneta n. sp.

Etymology: named after my children, Ido and Neta Shenkar.

Material examined: Israel, Gulf of Aqaba (Elat). 29°30' N, 34°56' E. Holotype: TAU-AS25430, sampled on March 7th, 2008 at 13m depth from the natural coral reef in front of the Inter University Institute. Paratype: TAU- AS 25228 (Oil port 20m, March 16th 2005), TAU-AS25258 (Oil port 14m, August 4th 2005), TAU-AS25501 (Oil port, 20m, March 15th 2005).

The National Collections of Natural History at Tel Aviv University, Israel.

External appearance

A solitary species with a cylindrical thorax 3–5cm long, which is often the only part of the animal that is visible. The tunic is smooth and free of epibionts. The body is divided into distinct abdominal and thoracic regions, connected by a narrow neck. The abdomen is often buried in cervices or coral branches with a firm attachment by the test that is ramified to branched root-like extensions ( Fig. 1 ). These well developed extensions of tough tunic are difficult to separate from the natural substrate, and often only the thorax part is available to observe. The 5–7 mm thick gelatinous tunic is completely uncolored and transparent allowing the branchial sac fine structure to be visible to divers even underwater ( Fig. 2). The siphons are simple round holes with six lobes in the branchial siphon, and eight lobes in the atrial siphon ( Fig. 3 a). In between the lobes there are 5–7 yellow (in live material) pigment spots ( Fig. 3 b).

Internal appearance

The body wall is thin and delicate. About 15–17 longitudinal muscle bundles stretch in parallel from both siphons to the ventral side, only few bundles are ramified toward the endostyle (figure Fig. 3 c). The oral siphon has about 12 circular muscles. There are 12 elongated oral tentacles, about 3 mm long. The tentacles are of one order size, and extend from the level of the third muscle band. No small tentacles were observed between the elongated tentacles. In a relaxed specimen with a 4 cm thoracic part, the opening of the branchial siphon measured about 0.7cm (specimen AS 25430). The atrial siphon too has about 12 bundles of circular muscles ( Fig. 3 a).

The perypharyngeal band has a single blade, slightly curved in a V-shape, with a protruding dorsal tubercle opening in a curved slit, about 1.3 mm in length ( Fig. 4 a). The large neural gland has a single pigment spot toward the dorsal side of the animal, is slightly branched, and lies below the dorsal tubercle ( Fig. 4 b). The dorsal lamina begins right after the first row of stigmata. It is constructed with numerous (about 40) triangle base pointy languets, as long as five rows of stigmata ( Fig. 4 c). The branchial sac is thin and flat with between 44–47 longitudinal vessels at each side, and 50–60 rows of stigmata. The holotype had 44 longitudinal vessels on each side, and 47 rows of stigmata. The stigmata are straight and There are about 4-5 stigmata per mesh ( Fig. 4 d). The rectum is long and goes side by side to the esophagus, with the anus and gonoduct opening posterior to the branchial sac toward the right side of the animal. The anus has two lips, each with about ten rounded small lobes ( Fig. 5 ). The genital papilla is constructed from four small lobes located at short distance under the anus ( Fig. 5 ).

The abdominal structures are not visible as the entire abdomen is embedded in an opaque pinkish tissue ( Fig. 1 ). However, it was possible to follow a white gonoduct on top of the stomach.

Figures

FIGURE 1. External appearance of Rhopalaea idoneta n. sp. Scale bar 1 cm. Paratype AS 25501

FIGURE 3. Rhopalaea idoneta n. sp. A. Atrial siphon, scale bar 1 mm B. Pigment dots in between the atrial siphonal lobes, scale bar 1 mm. C. Left side, scale bar 1 cm. Arrows pointing out to the longitudinal muscles.

FIGURE 4. Rhopalaea idoneta n. sp. A. Dorsal tubercle B. Neural ganglion C. Dorsal lamina D. Stigmata shape. Scale bar 1 mm. Photo: A. Gur

FIGURE 5. Rhopalaea idoneta n. sp. rectal region. Arrows pointing out to the genital papilla and anus.