Culeolus uschakovi Redikorzev, 1941

Culeolus uschakovi Redikorzev, 1941 View in CoL

( Figs 1B–I View Fig , 2 View Fig ; Tables 1–4)

Culeolus uschakovi Redikorzev, 1941: 183–185 View in CoL , 211, pl. 3, fig. 5, text-figs 10–13; Nishikawa and Ivanova 2024: 139– 143, text-fig. 1 (redescription of holotype).

Culeolus murrayi Herdman, 1881 View in CoL : Vinogradova 1970: 498– 502, table 3, text-figs 5–7.

Culeolus suhmi Herdman, 1881 View in CoL : Sanamyan and Sanamyan 2006: 331–333 View Cited Treatment , text-fig. 13.

Material Examined (identified by molecular analysis as cluster B). NSMT-Pc 6895–6904 (total 10 specimens), continental slope of Erimo Seamount , between Chishima-Kamchatka and Japan Trenches, from 41°20.79′N, 144°56.46′E to 41°20.52′N, 144°57.30′E, 6116–6131 m depth, R / V “Hakuho-maru” (KH-22-8-A3), 3 October 2022, Y GoogleMaps . Ise coll GoogleMaps .

Description. Morphological features of cluster B specimens outlined in Table 3, plus the following; Body proper 22–38mm long, with a hard (sclerified) stalk up to 220 mm long and 1.8 mm thick, rarely branching at midpoint. Proximal end of stalk running posteriad along anterior one-third to one-sixth of body mid-ventral line. Tunic dark brown, opaque, its whole surface densely covered with roundish to almost flat papillae, up to 500 µm in diameter. A ring of elongated conical projections, ventrally conspicuous, up to 3 mm tall, usually completely encircling atrial aperture ( Fig. 1B View Fig ) (sometimes incomplete and undetectable dorsally and/or dorsolaterally; Fig. 1C View Fig ); each conical projection covered densely with minute papillae, similar to those on tunic surface. In addition to the ring, nine similar conical projections, up to 1 mm tall (apparent anteroventrally on each side as a row extending approximately from branchial siphon to proximal end of stalk fused with body proper in NSMT-Pc 6901; Fig. 1D View Fig ). Mantle very thin, almost transparent, musculature a sparse network of thin fibers, except around apertures (dense with circular fibers). Branchial tentacles well developed, numbering up to 20, having second- and third-order branches; ciliated groove a simple elongated slit, C-, or S-shaped; dorsal languets conspicuous. Five or six branchial folds on each side [formulae: L. D. 3(12)4(10)8(8)5(6)4(4)4(3)3 V., R. D. 2(7)5(7)4(8)7(8)6(6)3(3)2 V. in NSMT-Pc 6896; L. D. 2(12)2(8)4(9)3(6)3(5)3 V., R. D. 2(10)2(7)4(9)3(8)2(4)2 V. in NSMT-Pc 6900]. Intestinal loop simple, usually C-shaped, elongated longitudinally ( Fig. 1H View Fig ), second loop sometimes detectable (but shallow) ( Fig. 1F View Fig ); stomach covered with complicated branched hepatic lobules. For variations in gonadal number and disposition, see “Morphological variations (cluster B)” (above). Gonads partly mature with ovarian eggs up to 400 µm in diameter. Dense horny polygonal spicules in mantle and viscera. Opaque white nemertean parasites in various parts of branchial sac in NSMT-Pc 6899, 6900, 6901, and 6903.

Remarks. Most specimens in the present material were similar to the holotype of C. uschakovi , both as originally described and redescribed by Nishikawa and Ivanova (2024), especially in the proximal insertion of the stalk running posteriad along the midventral line anteriormost part, the Culeolus- ridge being a series of elongated conical projections (projecting directly from tunic surface, unaccompanied by a common low tunic ridge) encircling the atrial aperture, five or six branchial folds on each side, two gonads on each side with one on the left in the intestinal loop, and each gonad with several lobes. A marked difference in the holotype (absent in most of the present specimens) was a dense wide belt of elongated conical projections on each side, from around the branchial aperture to the proximal end of the stalk fused with the body proper, forming an anteroventral “beard”. This difference may be modified by a row of some conical projections on each side anteroventrally near the branchial aperture in NSMT-Pc 6901; presence or absence of the “beard” may be regarded as an intraspecific variation in C. uschakovi . Further intraspecific variations in the species were found in the left gonadal number (two or three) and gonadal position (parallel to each other in the majority of specimens, but rarely a left gonad out of the loop and positioned longitudinally along the endostyle, or two right gonads with adjoined apertures). These structures may be significant in future taxonomic considerations of Culeolus .

Sanamyan and Sanamyan’s (2006: 331, text-fig. 13) 24 mm long specimen of C. suhmi from near the Aleutian Trench ( 4820 m depth) is similar to C. uschakovi in having a complete ring of elongated conical projections widely encircling the atrial aperture on the tunic and being most developed ventrally, its surface furnished wholly with low papillae, many of which included opaque matter. The specimen also had two gonads on each side, with one of the left gonads inside the intestinal loop. However, the authors noted that the specimen had “a few separate and relatively long papillae on the mid-ventral line”, especially between the posteroventral area of the ring towards the atrial aperture, with a similar but rather insignificant longitudinal row also detectable posterodorsally between the ring and aperture (see their text-fig. 13A), quite unlike the C. uschakovi holotype, which lacked such mid-ventral and posterodorsal rows of projections. Furthermore, the anteroventral “beard” present on the holotype was represented by only a very few large elements (three, according to the figure) in their C. suhmi specimen, somewhat reminiscent of NSMT-Pc 6901, although smaller and much more numerous in the holotype. These differences likely represent intraspecific variations among the NW Pacific populations, and Sanamyan and Sanamyan’s specimen of C. suhmi from near the Aleutian Trench is therefore included in the synonymic list of C. uschakovi .

Vinogradova’s (1970) specimens ( 55 in total) from NW Pacific deep water samples and identified as C. murrayi , although with limited morphological description, can be regarded as conspecific with C. uschakovi , following Sanamy- an and Sanamyan’s (2006: 333) recognition of their conspecificity with C. suhmi (= C. uschakovi ; see above) based on an examination of a “single intact medium-sized specimen in perfect condition” among Vinogradova’s specimens, collected at Station 5621 in the Chishima-Kamchatka Trench ( 5035–5210 m). Therefore, it should be noted that fig. 5 of Vinogradova (1970) depicting the whole body of a specimen from that station, clearly illustrated ca. 10 conical projections along each side of the proximal end of the stalk fused with the body proper, similar to the anteroventral “beard” on each side of NSMT-Pc 6901(see above; Fig. 1D View Fig ), as well as a ring of similar projections encircling the atrial aperture.

The validity of C. uschakovi and priority over C. suhmi and C. murrayi are considered by Nishikawa and Ivanova (2024).

Claude Monniot’s (1998: 555–557, fig. 6) records of C. pyramidalis Ritter, 1907 from the North Pacific included specimens from the Aleutian Trench ( 4867 m depth); his description was “based on the largest specimen” (ditto: 555), with inexact locality, including “its external appearance corresponds well to Ritter’s [original] drawing [reproduced] in Van Name (1945) ”. If C. Monniot’s description is applicable to the Aleutian material, it indicates the proximal end of the stalk running posteriad along the anterior mid-ventral line of the body proper, but with “larger papillae [= conical projections] found on a transverse line crossing each lateral side of the body” from each side of the atrial aperture “meeting at the ventral line” (loc. cit.). In its arrangement of projections on the Culeolus -ridge, the material clearly differed from C. uschakovi (a complete or nearly complete ring of projections widely encircling the atrial aperture). Claude Monniot’s (ditto) description further indicated the existence of a single 4- or 5-lobed gonad on each side, the left one inside the intestinal loop, quite unlike C. ushacovi (2–3 gonads on the right, and two gonads on the left, with one inside the loop). The significance of this condition remains unclear, as Ritter’s (1907: 16–18, pl. 2, figs 20, 21) original description of C. pyramidalis lacked gonadal information, saying only “Gonads not determined” (ditto: 17).

Distribution. Sea of Okhotsk, 3350 m depth ( Redikorzev 1941); Bering Sea, 3792–3954 m, Chishima-Kamchatka Trench, 4995–5210 m, and northern part of Japan Trench, 6156–6207 m ( Vinogradova 1970; as C. murrayi ); Near the Aleutian Trench, 4820 m ( Sanamyan and Sanamyan 2006; as C. suhmi ); Erimo Seamount, 6116–6131 m (present study).