Fimbrora calsubia

Description. Individual ca. 20 cm in length including oral siphon (Fig. 2 A, B). Tunic opaque and gelatinous; blood vessels running on surface of tunic (Fig. 2 B); fine warts, each about 0.5 mm in diameter, scattered evenly over entire tunic. Body attached to substrate with its posterior end (Fig. 2 A, B). Oral siphon enlarged, ca. 10 cm in diameter; single annular muscle strand running on outer edge of oral siphon; thread-like lobes, 52 in number, tightly arranged to each other on oral-siphon edge; single groove radially arranged on edge of oral siphon between base of each lobe; muscle strand associated to each lobe, running on inner wall of oral-siphon edge from lobe base for ca. 1 cm; beneath inner surface of oral siphon, neural cords radially running from neural ganglion (Fig. 2 C). Oral aperture situated 2.5 cm anterior to neural ganglion. Atrial siphon 1.5 cm in diameter; 37 blood vessels longitudinally running on surface of atrial siphon (Fig. 2 D). Body wall attached to tunic on oral siphon, heart and renal vesicles; irregular cavity existing between tunic and body wall; inner surface of tunic covered with epithelial tissue. Neural ganglion situated between oral siphon and atrial siphon. On base of oral siphon, 105 oral tentacles present, each being ca. 8 mm in length. Peripharyngeal band made of single lamina running in a short distance posterior to oral tentacles, forming V-shape posterior to neural gland aperture (Fig. 3 A); latter being single in number, almost straight in shape (Fig. 3 A) and opening at dorsal tubercle. Pharynx connected by mesenteries to peripharyngeal epithelium; mesenteries 0.5 - 3.0 mm in diameter (Fig. 3 B). Smooth dorsal lamina running along mid-line on ventral side of pharynx (Fig. 3 A, B). Longitudinal and transverse vessels running on inner surface of pharynx (Fig. 3 C); 6 - 10 stigmata without lateral cilia per mesh (Fig. 3 C). Secondary branchial papillae present on intersections of longitudinal and transverse vessels (Fig. 3 C). Digestive tract positioned on left side of body (Fig. 4 A). Oesophagus opening to left side of dorso-posterior part of pharynx. Stomach about 1.5 cm in length, having 10 folds, surrounded with renal vesicles (Fig. 4 A); multiple crustaceans (probably copepods) found in stomach lumen (Fig. 4 B). Intestinal loop S-shaped, having primary loop and secondary loop; intestine ca. 7 cm in length, ca. 5 mm in diameter (Fig. 4 A). Anus smoothly edged, opening close to atrial siphon (Fig. 4 A). Gonad situated proximally on intestinal loop (Fig. 4 C). Ovaries surrounded with male testis (Fig. 4 C, D). Oviduct and spermiduct running along secondary loop, opening close to anus (Fig. 4 A). Eggs contained in ovaries and oviduct, up to 0.2 mm in diameter (Fig. 4 D).

Figs 2, 3, 4

Material examined. One individual, JAMSTEC No. 111618, collected by N. Hookabe on 26 September 2022, about 400 km off the Pacific coast of middle Honshu, Japan, 30 ° 47.05 ' N, 138 ° 44.72 ' E, at a depth of 2027 m (Fig. 1).

Monniot C 1993, Indonesia Stations CP 4433, 2 specimens (MNHN P 5 FIM 8); CP 4435, 3 specimens (P 5 FIM 5 – P 5 FIM 6); CP 4436, 3 specimens (P 5 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 1991 a) 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 1991 a). 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.