Didemnum lambertae, 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 : 388-389

Didemnum lambertae sp. nov. Rocha & Neves

( Figs 6 , 7 )

Examined material: Holotype: MZUSP 0 0 0 91 one colony, Porto da Barra, Salvador, Bahia, 13°00'14” S, 38°32'01” W, 3 m, Col. R. M. Rocha, 0 9.12.2007. Paratypes: DZUP DID- 351 one colony, Germânia wreck, Salvador, Bahia, 13°00'34” S, 38°31'59” W, 6 m, Col. R. M. Rocha, 10.12.2007; DZUP DID- 352 one colony, Quebramar Norte, Salvador, Bahia, 12°57’52” S, 38°30’57” W, 5 m, Col. R. M. Rocha, 11.12.2007; DZUP DID- 353 one colony, Boião da Barra, Salvador, Bahia, 13°00'32” S, 38°32'19” W, 15 m, Col. R. M. Rocha, 12.12.2007; DZUP DID- 366 one colony, Quebramar Sul, Salvador, Bahia, 12°58’22” S, 38°31’09” W, Col. R. M. Rocha, 0 7.08.1999.

Etymology. Name given to honor Gretchen Lambert because of her many contributions to the knowledge of ascidian biodiversity.

Encrusting colonies are 5 to 20 cm long and about 3 mm thick. Colonies are red, some having cloacal apertures whit a white rim due to the presence of spicules but others uniformly colored ( Fig. 6 A). After preservation in formalin they turn white. Spicules are dense on the surface of the firm and brittle colony, and are less dense in the middle and basal layers of the tunic. Spicules are small and stellate, less than 25 µm in diameter, with long and cylindrical rays, rounded at the tip. There are six rays in optical transverse section ( Fig. 6 B).

Zooids are between 1.0 and 1.8 mm long, thorax and abdomen are equal in size. The oral siphon has six small triangular lobes. The atrial aperture is wide exposing the second and third rows of pharyngeal slits. The atrial languet is absent. The muscular process projects from the esophageal-rectal peduncle and it is shorter than the abdomen. Lateral organs are protruding between the third and fourth rows of stigmata, but shape varies among zooids: some are oval and other are z-shaped. Between 6 and 9 stigmata per row are on each side of the pharynx ( Fig. 6 D, 7A).

The esophagus is short; the stomach location and shape are typical, the duodenum is shorter than the stomach; the intestinal loop (with 2–3 constrictions) forms a deep secondary loop, covering the stomach. There are two small stolonic vessels. Gonads are located in the intestinal loop, one beside the other. The testis is single, spherical and surrounded by 7 coils of the sperm duct ( Fig. 6 C, 7B).The ovarium has one oocyte (0.3 mm). A few zooids were budding.

Larval trunk is oval, about 0.4 mm long, around which the tail winds half way. Larvae have three linearly arranged adhesive papillae with long stalks, plus five pairs of ectodermal ampullae. The sensory vesicle (including ocellus and otolith) is in the mid-dorsal region of the larval trunk ( Fig. 6 E, 7C).

Remarks. Colonies of Didemnum lambertae and D. flammacolor are similar in external appearance, but notable differences are in spicules (number and shape of rays), zooids (number of pharyngeal stigmata, size of lateral organs, shape of intestine and number of sperm duct coils), and larvae (number and shape of ampullae). Few species of Didemnum have larvae with 5 pairs of ampullae. Didemnum nekozita Tokioka, 1967 is found at greater depths (20–30 m), has posterior stomach and fewer stigmata in each half-row of the pharynx (five). Didemnum mutabile Monniot Monniot, 1987 has smaller larvae (0.28 mm) and larger spicules with short rays (35–40 µm) ( Monniot & Monniot 1987). Didemnum fuscum Sluiter, 1909 has larger spicules (60–90 µm), fewer stigmata in the pharynx (4–6 per half row) and 9 turns of the sperm duct. Didemnum pecten Kott, 2001 has larger spicules (56 µm) and 9 turns of the sperm duct. Didemnum poecilomorpha Monniot & Monniot, 1996 has larger spicules (60 µm), 8 turns of the sperm duct and larvae with symbiont algae. Didemnum sordidum Kott, 2001 has larger spicules (65 µm), smaller zooids (0.6 mm), and many granule brown cells in zooids and larvae ( Kott 2001). Didemnum domesticum Kott, 2004 has only six turns of the sperm duct ( Kott 2004).

Figures

FIGURE 6. Didemnum lambertae sp. nov. A, living colony. B, spicules. C, abdomen. D, thorax. E, larva. Scale bars: C – E = 0.5 mm.

FIGURE 7. Didemnum lambertae sp. nov. A, thorax. B, abdomen. C, larva. Scale bar: 0.5 mm.