Eudistoma illotum ( Sluiter, 1898 )

Monniot, Françoise, 2012, Some ascidians from the southern coast of Madagascar collected during the “ AtimoVatae ” survey, Zootaxa 3197, pp. 1-42 : 27-28

Eudistoma illotum ( Sluiter, 1898)

( Figure 22 A,B,C,D)

Distoma illotum Sluiter, 1898: 16 ;

Eudistoma illotum: Millar 1962: 160 fig; 24. Monniot et al 2001 and synonymy, South Africa.

Station. TR 6 (MNHN A3 EUD 354)

The largest of the 3 colonies is 6.5cm in length and 4cm thick. The colour in formalin is dull grey, and the consistency gelatinous without sand. The zooids open independently at the smooth surface of the colony, without systems ( Fig. 22 A). The less contracted zooids are 11mm long but most of them are shorter ( Fig. 22 C). Both siphons are short. The body wall is clear except some brown pigment cells located on the siphons and the transverse vessels. About 25 stigmata are in the first branchial row which is slightly curved dorsally. The gut loop is straight with well delimited segments ( Fig. 22 B,C). The gonads lie inside the gut loop. The heart is easily seen behind the gut loop. One or 2 brown larvae distend the atrial cavity. The trunk is 1mm long. The 3 adhesive papillae are well separated. A vesicle separates the dorsal and the median adhesive papillae and a bi-lobed vesicle separates the median and the ventral papillae. A vesicle is also present dorsally and ventrally to the adhesive papillae ( Fig. 22 D). In addition some irregular protrusions are located of the base of the papillae on each side. Ocellus and otolith are present, other organs of the trunk are not yet differentiated.

E. illotum was only recorded from South Africa.

Eudistoma pustulosum n. sp. ( Figure 22 E,F,G,H)

Etymology. In Latin pustulosus = with pustules

Station. TA 56 (MNHN A3 EUD 353 Holotype)

The single colony is a sheet 7x 5.5cm large and 0.8mm thick, completely embedded with sand. The surface is erected in small round protrusions as pimples ( Fig. 22 E), each of them containing the siphons of one zooid. The tunic is glassy, colourless and resistant. The zooids ( Fig. 22 F) occupy the whole thickness of the colony, perpendicular to the surface. The siphons are short with 6 lobes. The body wall is opaque and colourless. The thorax, always contracted, counts about 25 stigmata on each side in the median row. The abdomen narrow at its beginning is enlarged at the gonad level. The stomach is short, smooth walled, at 2/3 of the abdomen length. The intestinal loop is straight without individualised compartments. The gonads occupy a large part of the gut loop behind the stomach with very numerous testis vesicles in a bush and a central ovary. Small irregular shining crystals are scattered upon the gonad mass. Post-abdominal vascular processes are present. Two or three embryos are incubated in the atrial cavity distended even in less contracted zooids but which does not form a pedunculate pouch. The mature larva is 0.8mm long, colourless, with a tail in ¾ of a turn. The 3 adhesive papillae are divergent, sided by 4 large vesicles; the median ones are bi-dentate on each side or only one of them is bi-dentate on a side ( Fig. 22 G,H).

Among the sandy Eudistoma species of the Indian Ocean, this new species differs by the shape of the colony with both siphons of each zooid grouped in a surface protrusion of the tunic.

Figures

FIGURE 22. Eudistoma illotum: A, colony surface in formalin, B, abdomen; C, zooid; D, larva. Scale bars C = 2 mm; D = 0.5 mm. Eudistoma pustulosum: E, colony surface; F, zooid; G, H, larva. Scale bars; F = 2 mm; G, H = 0.5 mm.