Protoholozoa incrustans, Monniot, 2021

Monniot, Francoise, 2021, New records of deep-sea ascidians (Tunicata, Ascidiacea) from the New Caledonia region, Zootaxa 4996 (3), pp. 443-468 : 447-448

Protoholozoa incrustans sp. nov.

Figures 4 , 5

Station: Kanadeep 12-743-04. Two colonies (Syntypes MNHN A3 . PRO 8 – slides A3. 1494-1498) .

Both colonies form soft transparent crusts on sponges or didemnids. The largest colony ( Fig. 4 ) is 3 cm in extent and 1.5 mm in thickness. The glassy tunic contains sparse sand. The zooids do not show a particular design in their arrangement and their oral apertures could not be seen at the surface of the contracted colonies. The zooids are not perpendicular to the colony surface, the oral apertures being superficial but the atrial siphon is located deeper inside the colony thickness nevertheless no common atrial cavities obviously appear in the soft tunic. The thorax reaches 2.2 mm in maximum length and is followed without constriction by the abdomen 0.6 mm long ( Fig. 5A–C ). The oral siphon is short with 6 pointed lobes. The atrial siphon in posterior position is enlarged in an ampulla narrowed at its extremity with a dented rim ( Fig. 5A, C ). The body wall is thin and transparent; no muscles are present on the thorax except two long transverse fibres on each side at the base of the thorax which extend from the endostyle along the sides of the atrial siphon. Four to six short oral tentacles are present just below the oral rim. A prepharyngeal band encircles the base of the siphon. The pharynx contains 3 thick transverse branchial bars on each side attached ventrally to a long endostyle and which are dorsally linked to triangular rapheal papillae. The abdomen in continuity with the thorax contains a closed digestive loop. In less contracted zooids the stomach seems square-shaped with 4 low longitudinal crests. The hermaphrodite gonad forms a round mass inside and partly protruding out of the gut loop. No postabdominal process was detected. A single tadpole is often present inside the dilated atrial siphon ( Fig. 5A, C ). The larval body is 0.55 mm in diameter surrounded by a tail with one and a half turn ( Fig. 5D, E ). Three well spaced adhesive papillae are placed in a line between an arc of round vesicles on each side. An otolith is present.

According to the larval structure and its mode of incubation this new species belongs to the genus Protoholozoa Kott, 1969 as redefined in Monniot & Tatian (2020). Protoholozoa incrustans sp. nov. has common characters with Protoholozoa pigra Monniot F., 1974 collected from the Açores at 1000 m depth which possesses a flat encrusting colony and 3 transverse branchial bands. Protoholozoa incrustans differs from the Atlantic species by the thoracic musculature and the shape of the long inflated atrial siphon in which larvae are incubated. The larva of P. pigra and its incubation mode are unknown.

Protoholozoa pedunculata Kott 1969 has a cone-like colony on a peduncle; its larva is incubated in the thorax and has 3 adhesive papillae in a line.

Figures

FIGURE 5. Protoholozoa incrustans sp. nov. A, B, C, three zooids, scale bar = 0.5 mm; D, E, larvae, scale bar = 0.2 mm.

FIGURE. 4. Protoholozoa incrustans sp. nov. colony, scale bar = 1cm.