Diplosoma citrinum, Rocha, Rosana Moreira Da, Neves, Isabela Monteiro & Gamba, Gustavo Antunes, 2015

Rocha, Rosana Moreira Da, Neves, Isabela Monteiro & Gamba, Gustavo Antunes, 2015, New species of Didemnidae (Tunicata: Ascidiacea) from the tropical coast of Brazil, Zootaxa 3905 (3), pp. 381-396 : 391-394

Diplosoma citrinum sp. nov. Rocha & Gamba

( Figs 10 , 11 )

Examined material: Holotype: MZUSP 0 0 0 93 one colony, Ilha Escalvada, Guarapari, Espírito Santo, 20°42'00”S, 40°24'30”W, 1 m, col. R. M. Rocha, 12.02.2011. Paratypes: DZUP DIPL- 37 one colony, Ilha Escalvada, Guarapari, Espírito Santo, 20°42'00”S, 40°24'30”W, 12 m, Col. R. M. Rocha, 26.01.2012; DZUP DIPL- 38 one colony, Ilha Escalvada, Guarapari, Espírito Santo, 20°42'00”S, 40°24'30”W, 10 m, Col. R. M. Rocha, 27.01.2012; DZUP DIPL- 39 3 colonies, Boião da Barra, Salvador, Bahia, 13°00'32” S, 38°32'19” W, 10–13.5 m, Col. R. M. Rocha, 12.12.2007; DZUP DIPL- 40 one colony, Ondina, Salvador, Bahia, 13o00’33” S, 38o31’41” W, Col. R. M. Rocha, 0 6.06.2004.

Etymology. The name of the species refers to the yellow color of the living colony.

Colonies are encrusting 2–6 cm long, and very thin and delicate (1 mm thick). Living colonies have extensive cloacal cavities filled with water, which makes them appear thicker than they really are. The tunic is transparent and the yellow zooids are responsible for the colony color. When preserved in formalin zooids turn light brown. Zooids are arranged randomly without forming systems. Cloacal openings are circular, large and randomly distributed on the surface of the colony ( Fig. 10 A).

Zooids are embedded in a thin test and connected in pairs by thin projections of the test that extend to the basal layer of the colony, where the larvae are. Zooids are between 0.6 and 1.2 mm long. The oral siphon is tubular and short, with six rounded small lobes. The atrial opening exposes the second and third rows of stigmata. The muscular process projects from the base of the thorax and it is shorter than the abdomen. In the pharynx, the first row contains 8–10 stigmata, while the second and third have 7–9 and the fourth has 6–9 slits in each side ( Figs. 10 C, 11A).

The abdomen is larger than and perpendicular to the thorax. The esophageal-rectal peduncle is long. The stomach is large with an invagination in the region where it is penetrated by the esophagus, assuming a cordiform shape. The duodenum is shorter than the stomach and ends in a strong constriction. The anus has a smooth margin at the level between the third and fourth rows of stigmata ( Figs 10 C, 11D). There are two or three stolonic vessels.

Gonads are inside the intestinal loop, which means they appear underneath the abdomen, because the intestine is horizontally oriented. The testis has one spherical follicle. There is a large (0.3 mm) and another smaller oocyte. Budding was observed in many zooids ( Fig. 10 C).

Larvae were found only in colonies collected in Espírito Santo. They are gemmiparous with the trunk 0.6 mm long; the tail winds a little more than halfway around the trunk. Three adhesive papillae are present with long stalks, positioned a distance from each other, with three pairs of short, finger-like ampullae. The oozooid pharynx has four rows of stigmata with 7−8 slits in the first and second rows and 4−6 in the third and fourth rows ( Figs. 10 B, 11C).

Remarks. Of the species of Diplosoma found in the Atlantic, only D. singulare Lafargue, 1968 has one follicle in the testis. However, in that species, the abdomen is vertical with gonads on the right side, with non gemmiparous larva having four pairs of ampullae ( Lafargue 1968). In other waters, among species with one follicle in the testis, D. ata Monniot & Monniot, 1987 has the oral siphon with six very long leaf-like lobes and pigmented cells, the pharynx has at least 10 slits in each half row, and the larva has a larger number of ampullae ( Monniot & Monniot 1987). Diplosoma pannosum Monniot & Monniot, 2001 differs from D. citrina by the color of the colony and number of ectodermal ampullae in the larva. Diplosoma unitestis Monniot & Monniot, 2001 has a unique ovary isolated within a pouch and D. redika Monniot, 1994 has uncolored colonies and larvae with four pairs of ectodermal ampullae and three embryos ( Monniot & Monniot 2001).

Figures

FIGURE 10. Diplosoma citrinum sp. nov. A, living colony (yellow bar = 5 cm). B, larva. C, zooid without tunic. Scale bars: B, C = 0.5 mm.

FIGURE 11. Diplosoma citrinum sp. nov. A, thorax. B, abdomen (posterior view). C, larva. D, zooid. Scale bar: 0.5 mm.