Fimbrora calsubia Monniot C & Monniot F, 1991

Monniot, Françoise & López-Legentil, Susanna, 2017, Deep-sea ascidians from Papua New Guinea, Zootaxa 4276 (4), pp. 529-538 : 531-533

Fimbrora calsubia Monniot C & Monniot F, 1991

Monniot C & Monniot F, 1991, New Caledonia

Monniot C 1993, Indonesia

Stations CP 4433, 2 specimens (MNHN P5 FIM 8); CP 4435, 3 specimens (P5 FIM 5 – P5 FIM 6); CP 4436, 3 specimens (P5 FIM 7)

The genus Fimbrora clearly belongs to the family Ascidiacea, exhibiting a branchial sac well developed with longitudinal vessels and true stigmata, although it may be confused with an Octacnemidae at first look. The newly collected specimens corresponded well with previous observations reported for the single species described for the genus Fimbrora calsubia , and previously collected near New Caledonia (Monniot & Monniot 1991a) and in Indonesia (Monniot 1993).

These large ascidians were attached to stones by a wide basal disk covered with dense filaments ( Fig. 1 A). The tunic is transparent and thin on the oral lobes but thicker basally. The total body length reaches 15 cm. The oral aperture is a wide funnel with the free edge prolonged by numerous thread-like lobes ( Fig. 1 A, B). A complex system of blood vessels can be seen through the transparent oral siphon as previously described and depicted (Monniot & Monniot 1991a). The tunic adheres to the body wall on the oral siphon but not on the abdominal region where a large cavity appears between the abdomen and the base of the body attached to the substrate. This cavity seems empty, but this may be due to strong contraction of the specimens fixed in ethanol. On the inner side of this posterior sac-like tunic protrude some ramified opaque tissue growth with no differentiated structure ( Fig.1 B) but stainable with haemalum ( Fig. 1 D); three to four of these structures are present in all specimens. The atrial siphon opens as a simple hole with a smooth rim on the dorsal side ( Fig. 2 B) near the neural area, slightly on the right side.

The musculature on the oral funnel comprises annular fibres at the edge of the thread-like lobes, and radial fibres crossing this ring become thinner when prolonged on the sides of the siphon. A strong sphincter surrounds the mouth aperture. Crossed muscular fibres enclose the abdominal part. Numerous short filiform tentacles arise from the mouth entrance. The neural ganglion ( Fig. 1 C) and the small neural gland are enclosed together in a small “V” of the prepharyngeal band. From the point of this “V” start two rapheal crests uniting posteriorly in a single lamina that increases in height to reach the bottom of the branchial sac ( Fig. 2 A). The branchial tissue is thin and flat ( Fig. 2 A) and is attached to the body wall by a few, thick strong bridles. There is an average of 45 to 50 longitudinal vessels on each side. The transverse vessels are different sizes with an irregular pattern ( Fig. 2 A). Ten to twelve elongated stigmata can be counted between two successive longitudinal vessels. No stained cells that would suggest the presence of ciliae appeared around the stigmata.

The different parts of the gut loop formed a dense mass and were not individualized. The gonad is massive and attached to the gut and no gonoducts were observed. The morphology of this newly collected species corresponded well to previous observations and does not vary across distant geographic locations from Indonesia to New Caledonia.

Figures

FIGURE 1. Fimbrora calsubia. A and B, ventral and dorsal sides of a specimen. C, neural area. D, detail of the ramified tissues of the posterior part of the abdomen stained with hemalum.

FIGURE 2. Fimbrora calsubia. A, branchial tissue stained with haemalum. B, body without tunic showing the atrial aperture. Scale bars 1 cm.