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).