Ziminella abyssa, Korshunova, Tatiana, Martynov, Alexander, Bakken, Torkild, Evertsen, Jussi, Fletcher, Karin, Mudianta, I Wayan, Saito, Hiroshi, Lundin, Kennet, Michael Schroedl, & Picton, Bernard, 2017

Korshunova, Tatiana, Martynov, Alexander, Bakken, Torkild, Evertsen, Jussi, Fletcher, Karin, Mudianta, I Wayan, Saito, Hiroshi, Lundin, Kennet, Michael Schroedl, & Picton, Bernard, 2017, Polyphyly of the traditional family Flabellinidae affects a major group of Nudibranchia: aeolidacean taxonomic reassessment with descriptions of several new families, genera, and species (Mollusca, Gastropoda), ZooKeys 717, pp. 1-139 : 16-18

Ziminella abyssa sp. n. Fig. 12

Type material.

Holotype, ZSM Mol-20100647, 19 mm long (fixed), R/V ‘‘ Akademik Lavrentyev", sta. B5-10, 24.08.2010, The Sea of Japan, depth 2676 m. 8 paratypes, ZMMU Op-248, up to 20 mm long (fixed), R/V ‘‘Vityaz’’, sta. 6657, 15.06.1972, The Sea of Japan, depth 3560 m. 9 paratypes, ZMMU Op-249, up to 24 mm long (fixed), R/V ‘‘Vityaz’’, sta.7462, 29.05.1976, The Sea of Japan, 41°19.8'N, 131°15.2'E, depth 3290 m. 57 paratypes, ZMMU Op-250, up to 25 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7463, 29.05.1976, The Sea of Japan, 40°45.0'N, 131°16.0'E, depth 3300 m. 1 paratype, ZMMU Op-252, 9 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7476, 06.06.1976, The Sea of Japan, 40°39.5'N, 132°32.8'E, depth 3425 m. 7 paratypes, ZMMU Op-253, up to 15 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7479, 07.06.1976, The Sea of Japan, 39°09.1'N, 131°03.2'E ,, depth 3120 m. 2 paratypes, ZMMU Op-255, up to 14 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7492, 12.06.1976, The Sea of Japan, 38°21.8'N, 134°49.5'E, depth 3020-3030 m. 2 paratypes, ZMMU Op-256, up to 19 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7494, 14.06.1976, The Sea of Japan, 38°48.0'N, 136°04.6'E, depth 2740 m. Two paratypes, ZMMU Op-257, 15 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7496, 01.07.1976, The Sea of Japan, 40°36.60'N, 139°00.002'E, depth 3340 m. 48 paratypes, ZMMU Op-258, up to 21 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7517, The Sea of Japan, 42°28.2'N, 138°20.9'E, depth 3620 m. 6 paratypes, ZMMU Op-259, up to 18 mm long (fixed), R/V ‘‘Vityaz’’, sta. 7519, 02.06.1976, The Sea of Japan, 41°28.8'N, 136°06.1'E, depth 3460 m. 11 paratypes, ZMMU Op-264, up to 12 mm long (fixed), R/V ‘‘ Akademik Lavrentyev’’ (SoJaBio), sta. A3-11, 14.06.2010, The Sea of Japan, 44°47.6338'N, 137°15.3182'E, depth 1494-1525 m.

Type locality.

The Sea of Japan.

Etymology.

From abyssum (= depth, Latin) in reference to abyssal habitat of the new species, one of the deepest among aeolidacean nudibranchs.

Diagnosis.

Continuous notal edge, lateral branches of digestive gland (ceratal basis) dark violet, rachidian tooth with up to 30 (and more) fold-like or fork-shaped denticles clearly delineated from central cusp, lateral teeth with few denticles on teeth edge, receptaculum seminis not evident, penis elongate conical.

Description.

External morphology (Fig. 12A, B). Body wide. Foot and tail wide, anterior foot corners short. Rhinophores similar in size to oral tentacles, smooth to slightly wrinkled. Dorsal cerata elongate, thin, continuously attached to well-defined uninterrupted notal edge without forming clusters. Apices of cerata pointed. Notum narrow but distinct throughout both lateral sides of body. Digestive gland diverticulum fills significant volume of the cerata. Anal opening on right side below notal edge close to middle body part. Reproductive openings on right side. Tail long and pointed, extending only short distance beyond last cerata

Colour. Background colour translucent milky white. Digestive gland diverticula probably reddish. Rhinophores light orange at the bases and pale on most of the rest of the length. Lateral branches of digestive gland (that shine through lateral dorsum sides) characteristically dark violet (estimated from a field colour photograph).

Jaws (Fig. 12C, D). Jaws broad, yellowish in colour. Masticatory processes of jaws covered with several compound denticles.

Radula (Fig. 12 E–H). Radula formula up to 40 × 1.1.1 (in adult specimen 20-24 mm in length). Rachidian tooth with strongly protracted non-compressed cusp of ca. 1/3 of the tooth length (Fig. 12E). Rachidian tooth bears up to 30 (and more) special, fold-like or fork-like lateral denticles, which are sometimes greatly disordered. Larger denticles typically intermingled with the smaller ones. Cusp is clearly delineated from the adjacent first lateral denticles. Lateral teeth (Fig. 12 F–H) narrowly triangular with few small denticles on internal edge.

Reproductive system (Fig. 12J). Diaulic. Hermaphroditic duct leads to long, relatively narrow convoluted ampulla of several whorls. Vas deferens extremely long, without distinct prostate. Penial sheath elongated. Penis entire, conical. Oviduct connects through insemination duct into female gland complex. No distal or proximal receptaculum seminis detected.

Ecology.

Deep sea basins at 1494-3620 m depth, soft bottom. This species is most common in the deepest parts of the Sea of Japan at about 3000 m. Upper bathymetric limit needs to be refined. Feeds on sea anemones of the family Edwardsiidae .

Distribution.

Central deepest basins of the Sea of Japan.

Remarks.

By presence of an entire copulative organ Z. abyssa sp. n. is similar to Z. japonica (Volodchenko, 1941), but clearly differs in the pattern of the rachidian radular teeth. While Z. japonica has regular lateral denticles of the rachidian teeth, all similar in size, no more 20 in number even in very large specimens (30 mm), Z. abyssa sp. n. has highly irregular lateral denticles of the rachidian teeth, different in size, fold- and fork-shape (Fig. 12F, G), sometimes even placed disorderly (Fig. 12H), up to at least 30 (and more) in number even in specimens which are much smaller than in the previous species with specimens reaching 20-24 mm in length. Remarkably, the irregularity of the rachidian teeth in Z. abyssa sp. n. persists even in very small juveniles (2 mm), in which larger denticles already intermingle with the smaller ones (Fig. 12I). The morphological differences between these two species agree with the considerable bathymetric differences: Z. japonica is a shelf and upper bathyal species (ca. 100-500 m), whereas Z. abyssa sp. n. inhabits predominantly the deepest (approximately 3000 m) basins of the Sea of Japan.