Eudistoma repens Millar 1977

Monniot, Françoise, 2016, Ascidians (Tunicata) of the French Guiana Expedition, Zootaxa 4114 (3), pp. 201-245 : 213

Eudistoma repens Millar 1977

Figure 8 .

Stations. SS1; SS3; SS4; SS10; SS12; SC13; SD8; CP4386; CP4408.

The colonies are large with many short cylindrical lobes erect on a thick basal crust ( Fig. 8 A). The tunic is entirely incrusted with sand. The oral siphons are slightly protruding from the flat upper colony surface ( Fig. 8 B) The zooids are all contracted ( Fig. 8 E) with 5mm in total length and lie at the top of the colony lobes. Both siphons have 6 pointed lobes ( Fig. 8 F). The thoracic wall is thick and opaque. The numerous oral tentacles in 2 orders of size are placed on 2 rings. In the branchial sac the first row of stigmata curves dorsally 20 stigmata were counted in the second row on the right side. The round stomach is followed by an annular widening. The rectum begins with a caecum and then forms a deep curve perhaps a result of contraction. An average of 20 testis vesicles occupies the gut loop. Two or 3 larvae are enclosed into the atrial cavity. Their trunk is 0.65mm long with a tail in a half turn ( Fig. 8 C). Lateral to the 3 medial adhesive papillae 8 to 10 bifid ampullae make a thick coating. The above description corresponds to that of Millar (1977).

E. repens and E. carolinense were found together in several dives and even sometimes fixed on each other. The difference between them is difficult to see at first sight when the colony lobes are small. In E. repens the top surface of the lobes appears granular due to the protrusion of the siphons; the tunic is softer and the zooids have a strong longitudinal musculature. The size of the larva is very different in both species.

Rocha & Moreno (2000) recorded colonies of E. carolinense from Brazil but without description. Oliveira et al (2014) considered E. repens as a synonym of E. carolinense for Brasilian specimens but their description mentions an opaque and muscular body wall, several oocytes in the atrial cavity (characters of the former species) but larvae only 0.4mm in length (the size in E. carolinense ). They also represent different colony shapes ( Figs 13–14 ). These colonies likely belong to a mixture of two species.

Figures

FIGURE 8. Eudistoma repens. A colony; B, pieces of other colonies; C, three larvae, scale bar = 0.2 mm; D, thorax; E contracted zooid; F, siphons. C to F stained with hemalum.

FIGURE 13. Ecteinascidia aranea n. sp. A, part of a colony in formalin; B two zooids, scale bar = 1 cm; C, zooid ventrally opened and stained; D, gonad; E, neural area.

FIGURE 14. Ascidia curvata. A, left side of the body removed from tunic. Body opened along the ventral line and stained, scale bar = 5 mm; C, tentacles and neural area; D, part of the dorsal lamina.