Didemnum aurantium, 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 : 383-386

Didemnum aurantium sp. nov. Rocha & Neves

( Figs 2 , 3 )

Examined material: Holotype: MZUSP 0 0 0 50 one colony, Quebramar Norte, Salvador, Bahia, 12°57’52” S, 38°30’57” W, 5 m, Col. R. M. Rocha, 11.12.2007. Paratypes: DZUP DID- 354 one colony, Canal Madre Deus, Salvador, Bahia, 12°45’48” S, 38°39’17” W, Col. R. M. Rocha, 07.06.2004; DZUP DID- 355 one colony, Quebramar Norte, Salvador, Bahia, 12°57’52” S, 38°30’57” W, Col. R. M. Rocha, 08.06.2004; DZUP DID- 356 one colony, Quebramar Sul, Salvador, Bahia, 12°58’22” S, 38°31’09” W, Col. R. M. Rocha, 10.06.2004; DZUP DID- 357 one colony, Naufrágio Germânia, Salvador, Bahia, 13°00'34” S, 38°31'59” W, 6.5 m, Col. R. M. Rocha, 10.12.2007; DZUP DID- 358 one colony, Iate Clube, Salvador, Bahia, 12°59’57” S, 38°31’52” W, 3 a 4 m, Col. R. M. Rocha, 13.12.2007; DZUP DID- 384 7 colonies, Quebramar Norte, Salvador, Bahia, 12°57’52” S, 38°30’57” W, 5 m, Col. R. M. Rocha, 11.12.2007.

Etymology. The name refers to the bright orange color of the colony under water.

The colonies are bright orange (ranging between darker and lighter oranges) with slightly darker cloacal cavities ( Fig. 2 A) and variable in size, ranging from 1.5 to 5.0 cm in length. When filled with water the large cloacal cavities give the colony surface a hilly appearance. When fixed in formalin, colonies are very thin (about 1 mm) and become white with some rose-colored spots. Clumps of orange pigment were found in the tunic during the dissection of some colonies. Spicules are abundant in the surface layer of the colony, giving them a firm, brittle consistency. Spicules are less abundant in the middle and lower layers of the tunic. Spicules which are smaller (30 mm) are stellate and have eight long or short conical rays in optical transverse section. Larger spicules (40 to 50 mm) tend to have longer and fewer rays ( Fig. 2 B). Zooids are about 1 mm long and are difficult to remove from the tunic. Oral siphons have six small lobes. The atrial aperture is wide and exposes most of the pharynx and the atrial languet is absent. The muscular process projects from the base of the thorax and is variable in length, but is usually shorter than the abdomen. Thoracic lateral organs protrude, with variable shape, 35 to 45 µm in maximum length, and they are located between the third and fourth row of pharyngeal stigmata. The pharynx has four rows of stigmata and 5 to 7 slits per row on each side ( Fig. 3 A).

The abdomen is slightly larger than the thorax and stolonic vessels were not observed. The stomach is rounded. The duodenum is shorter than the stomach. The intestinal loop forms a shallow secondary loop, that can pass beside the stomach or slightly overlay it. Gonads are within the intestinal loop. The testis has a unique and spherical follicle surrounded by 8 to 10 narrow and tightly packed turns of the sperm duct ( Fig. 3 B). The ovarium has a large (0.2 mm) and smaller oocyte. Budding in the esophageal region was observed in a few zooids.

Mature larvae were found in only one colony that was collected during the winter (June 2004) and immature larvae were found in a single colony during the summer (December 2007). Larvae are more elongate than wide (0.47 mm trunk length) and the tail winds three-quarters of the way around the trunk. Larvae are not pigmented, have three linearly arranged adhesive papillae on thin stalks, plus four pairs of finger-like ectodermal ampullae. The sensory vesicle (with otolith and ocellus) is in the mid-dorsal region of the larval trunk ( Figs. 2 C, 3C).

Remarks. Many Didemnum species have orange colonies, but all descriptions available are different from Didemnum aurantium n. sp. Didemnum ahu and D. inauratum Monniot, 1983 have spicules with rounded ray tips, which are pointed in D. aurantium ( Monniot 1983; Rocha et al. 2005). Didemnum drachi Lafargue, 1975 , D. peyrefittense Brément, 1913 , D. coriaceum Von Drasche, 1883 and D. ligulum have a greater number of ectodermal ampullae in the larvae than D. aurantium ( Lafargue 1975; Rocha & Monniot 1995). Didemnum granulatum differs by the presence of papillae filled with spicules on the tunic surface ( Tokioka, 1954).

Figures

FIGURE 2. Didemnum aurantium sp. nov. A, living colony. B, spicules. C, larva. Scale bar: C = 0.5 mm.

FIGURE 3. Didemnum aurantium sp. nov. A, thorax. B, abdomen. C, larva. Scale bar: 0.5 mm.