Culeolus tenuis Vinogradova, 1970

Peeran, Syed Wali, Murugan, Manohar, Doggalli, Nagabhushana, Fageeh, Hytham, Ibrahim, Wael, Al-Ak'hali, Mohammed Sultan & Basheer, Syed Nahid, 2023, Culeolus tenuis (Urochordata, Ascidiacea) Newly Found off Fukushima, Japan in the Japan Trench, Bulletin of the National Museum of Nature and Science. Series A, Zoology 49 (2), pp. 75-80 : 76-78

Culeolus tenuis Vinogradova, 1970

( Figs. 1–2; Table 1)

Culeolus tenuis Vinogradova, 1970, pp. 491–493 , textfigs. 1–2; Sanamyan and Sanamyan, 1998, p. 214; Sanamyan and Sanamyan, 2006, pp. 329–331.

Culeolus sp. : Kuramochi et al., 1999, pp. 1–3, photos 1–3.

Material examined (Deposited in National Museum of Nature and Science, Tsukuba). NSMT-Pc 5353, land-slope side of Japan Trench off Fukushima Prefecture, Japan (36°23′86.72″N; 143°45′59.96″E), 5,784 m, T. Kuramochi [from remote-operated submersible lKAIKOz supported by JAMSTEC R / V lKAIREIz (KR98-07 #79 Leg. 1)], 15 July 1998 .

Description. Body proper pale pink, gonads visible through tunic, with a long brownish stalk (in situ observation), but body proper later becoming brown ( Kuramochi et al., 1999, p. 2, photos 1–3); brownish coloration persisting for several years following formalin-fixation and 70%-ethanol preservation, subsequently becoming pale yellow (same preservative) by early 2023. Body length 68 mm, width 22 mm, and dorsoventral depth 35 mm; a long blackishbrown stalk, ca. 365 mm (length), 2.5 to 3 mm (diameter), distal end fixed in bottom substrate, proximal end running posteriad along anterior half of mid-ventral line of body ( Fig. 1A, St); stalk comprising a dark brown, hard, wire-like but relatively fragile shaft, covered with thin, almost transparent tunic layer; body tunic thin, tough, semi-transparent whitish, entire surface densely covered with pale to moderately dark brownish papillae, up to 0.2 mm high (coloration becoming pale yellow by early 2023); both siphons indistinct, branchial aperture terminal, widely opened with many protruding branched tentacles, atrial aperture situated at posterior onefifth of body, very wide with anal end of intestine exposed on left; a distinct low U-shaped crest widely opened dorsally, running from antero-lateral aspect to posteroventral aspect of atrial aperture on each side to unite at mid-ventral line ( Fig. 1A). Mantle very thin, white (almost transparent), body musculature a sparse network of very thin fibers, except around apertures (furnished densely with circular fibers). Branchial tentacles 28 in total, including both second- and thirdorder branches (sensu Tokioka, 1953); ciliated groove C-shaped, opening to right ( Fig. 1D), many distinct dorsal languets following posteriorly, with six branchial folds on each side (formula: L. D. 3(14)2(17)2(15)4(15)4(12)4(6)10 V.; R. D. 2(13)3(17)2(16)4(14)4(12)4(7)8 V). Intestinal loop simple, U-shaped, elongated longitudinally; stomach extensively covered with complicatedly branched hepatic lobes ( Fig. 1C). Three partly matured, longitudinally elongated gonads on each side, each comprising several lobes discernible as simple or complicated endocarps, two gonads in tight contact with each other along dorsal aspect of decending limb of gut loop, a third gonad occupying first intestinal loop on left ( Fig. 1C), all three in close contact with one another along epicardium on right ( Fig. 1B), each gonad furnished distally (near atrial siphon) with a free elongated end of sperm duct, accompanied by almost sessile end of oviduct ( Fig. 1E); ovarian eggs up to 0.6 mm in diameter; nongonadal endocarps absent from mantle and intestinal surface facing peribranchial cavity. Flat, yellowish or white (almost transparent) polygonal horn-shaped spicules up to 1.5 mm long discernible densely in walls of branchial sac, pericardium (not heart), intestine (including hepatic lobes), and gonads ( Fig. 1F).

Remarks. The present specimen is closely similar to the original description of C. tenuis given by Vinogradova (1970) for 40 syntype specimens (holotype not designated) from 6 stations in the NW Pacific at depths of 5,027 to 6,282 m; in particular, in the proximal end of the stalk running along the anteroventral aspect of the body, the tunic crest U-shaped and opening dorsally, the dense visceral distribution of horny spicules, 6 distinct branchial folds, a simple ciliated groove, simple U-shaped intestine, and 3 elongated, (almost always) lobed and endocarpbearing gonads on each side, opening near the atrial aperture. The position of the ventral-most gonad on the left (i.e., within the first intestinal loop or not), seems to be a significant diagnostic character within the genus, but the original description of C. tenuis lacked that detail. An attempt (by TN) to examine the syntypes of C. tenuis , deposited at the P. P. Shirshow Institute of Oceanology of Russian Academy of Sciences, Moscow ( Vinogradova, 1970, p. 490), was unsuccessful. However, Sanamyan and Sanamyan (2006) described ltwo intact specimensz of C. tenuis , collected at [ R / V bVityaz`] lSt. 5621, 5030–5031 mz and lidentified as Culeolus tenuis by Vinogradovaz (p. 330) [part of Vinogradova`s (1970) 10 syntypes from the bVityaz` station 5621 (K. Sanamyan, personal communication; see Tab. 1)], as having three elongated lobed gonads on each side, with one of the left gonads included in the first intestinal loop. In gonadal number and arrangement, therefore, the present specimen from the Japan Trench is identical to those described by Sanamyan and Sanamyan (2006), supporting the identification of the specimen col- lected off Fukushima. The description by Sana- myan and Sanamyan (1998) of a single non-type specimen of C. tenuis from the Aleutian Trench noted only two gonads (instead of three) on the right side, whereas the number and arrangement of left gonads matched the description in Sanamyan and Sanamyan (2006) of specimens from the Kurile-Kamchatka Trench, as well as the present Japan Trench specimen. The taxonomic status of the Aleutian specimen should be reconsidered following examination of further material.

Sanamyan and Sanamyan (2006) noted specimens as having the tunic surface lalmost smooth, without papillaez (p. 330), Vinogadova (1970) having earlier described the tunic surface in some specimens as being furnished with irregularly-shaped flat papillae at the posterior end of the body (p. 493). However, the entire body surface of the present specimen was densely covered with minute papillae. Any taxonomic significance of this difference is presently ques- tionable, and requires further investigation.

Although Monniot and Monniot (1991, p. 421) regarded C. sluiteri Ritter, 1913 from the NW Pacific as lpeut-être synonyme dez (perhaps a synonym of) C. tenuis , they overlooked the presence of only lfive prominent (branchial) folds on each sidez ( Ritter, 1913, p. 464) in the former species, compared with six in C. tenuis , as noted by Sanamyan and Sanamyan (1998, 2006). Thus, C. tenuis can be regarded as valid, being distinct from C. sluiteri . Although Sanamyan and Sanamyan (1998, 2006) questioned the validity of C. nadejdae Sanamyan, 1992 as a species distinct from C. tenuis , the former is so far known only from the Sea of Okhotsk, in 1,050 – 1,040 m depth ( Sanamyan, 1992, pp. 188–190), and is clearly distinguishable from C. tenuis by the number and arrangement of left gonads [total of 2–5, all in the first intestinal loop in the former; 3 (one in the loop) in the latter], as correctly noted by Sanamyan and Sanamyan (2006).