Didemnum flammacolor Rocha, Neves & Gamba, 2015, sp. nov.

Didemnum flammacolor sp. nov. Rocha & Neves

(Figs 4, 5)

Examined material: Holotype: MZUSP 0 0 0 90 one colony, Ondina, Salvador, Bahia, 13o00’33” S, 38o31’41” W, Col. R. M. Rocha, 0 6.06.2004.

Etymology. The name refers to the red color of the living colony.

The encrusting colony is approximately 3 cm long and 1 mm thick. Colony surface is red and the rim of cloacal cavities is white due to the presence of spicules (Fig. 4 A); when fixed in formaldehyde, the color fades to pinkish. Spicules are abundant throughout the surface, giving the colony a firm and brittle consistency; spicules are less abundant in the middle and lower layers of the tunic. Spicules are stellate, approximately 30 Μm in diameter with eight tapered rays in cross section; some spicules are approximately 20 Μm in diameter and have 7–10 conical and truncated rays in optical transverse section (Fig. 4 B).

Zooids are about 1 mm long. The oral siphon has six small triangular lobes. The atrial aperture is wide open, exposing most of the pharynx and an atrial languet is absent. The muscular process projects from the esophagealrectal peduncle and is variable in length and may be absent in some zooids, and tends to be shorter than the abdomen. Thoracic organs are circular, 80 µm in length, protruding, at the level of the fourth row of pharyngeal slits. There are between 6 and 7 stigmata per row on each side of the pharynx (Fig. 5 A).

The abdomen is larger than the thorax. One small stolonic vessel was observed in some zooids. The esophagus is short. The location and shape of the stomach are typical; the duodenum is shorter than the stomach; the intestinal loop forms a deep secondary loop, covering the stomach. The single testis is spherical and surrounded by nine coils of the sperm duct (Fig. 5 B). No oocytes were found.

Larvae are oval, trunk is approximately 0.4 mm in length, around which the tail winds three-quarters of the way. Larvae are non-pigmented, have three linearly arranged adhesive papillae that are close together on short stalks, plus four pairs of rounded ectodermal ampullae. The sensory vesicle (including ocellus and otolith) is in the mid-dorsal region of the larval trunk (Figs. 4 C, 5C).

Remarks. The known Didemnum species with reddish colonies differ from D. flammacolor in many ways. Didemnum moseleyi (Herdman, 1886) and D. pseudofulgens Médioni, 1970 have spicules with a greater number of short, conical rays (Kott 2001; Médioni 1970). Didemnum rodriguesi colonies have a reticulate pattern on the surface of the tunic and a different number of larval ampullae (Rocha & Monniot 1993; Monniot 2010). Didemnum membranaceum Sluiter, 1909 has larger spicules (0.1 mm) with 4–6 conical rays in transverse optical section (Monniot & Monniot 2008). Didemnum madeleinae Monniot & Monniot, 2001 have larvae with 12 or more pairs of ampullae and the trunk is longer (Monniot & Monniot 2001). Didemnum coccineum Von Drasche, 1883 and D. amourouxi Lafargue, 1976 also have a greater number of ampullae but only two adhesive papillae (Lafargue & Wahl 1987). Some other species of Didemnum have 9 turns of sperm duct and larvae with 3 adhesive papillae and 4 pairs of ampullae. Didemnum crescente Kott, 2001 has larger spicules (70 µm), longer retractor muscles and 0.6 mm long larval trunk (Kott 2001). Didemnum cuculiferum (Sluiter, 1909) has longer retractor muscle and larger larvae (0.57 mm). Didemnum fragilis Sluite 1909, has a fragile colony with circular spicules and larger larvae (0.78 mm) (Monniot & Monniot 1987). Didemnum hiopaa Monniot & Monniot, 1987 form small and transparent colonies and has spicules with larger number of rays. Didemnum incantum (Herdman, 1899) has longer retractor muscle, fewer pharyngeal stigmata in each row (4–6), and the spicules rays have a tetrahedral basis. Didemnum vulgare Kott, 2001 has larger spicules (60 µm) with more rays and longer retractor muscle (Kott, 2001).