Deep-water ascidians (Tunicata: Ascidiacea) from the northern and western Pacific Author Sanamyan, K. E. Author Sanamyan, N. P. text Journal of Natural History 2006 2006-05-31 40 5 - 6 307 344 http://dx.doi.org/10.1080/00222930600628416 journal article 10.1080/00222930600628416 1464-5262 4669378 Culeolus tenuis Vinogradova, 1970 ( Figure 12 ) Culeolus tenuis Vinogradova 1970 , p 941 ; Sanamyan and Sanamyan 1998 , p 214. Figure 12. Culeolus tenuis Vinogradova, 1970 . (A) Intact specimen (whole stalk not shown); (B) specimen opened along ventral mid line; branchial sac removed to show gut, gonads, and muscles. Material examined St. 5621, 5030– 5031 m , two intact specimens identified as Culeolus tenuis by Vinogradova. Description The body length of the examined specimen is 22 mm , the entire peduncle is 126 mm long and 0.7–0.9 mm diameter. The surface of the pale yellowish test is almost smooth, without papillae. The postero-ventral crest consists of a low thick lamella crossing the mid-ventral line in the postero-ventral point of the body and continuing obliquely along each side to end halfway between the siphons, not reaching the dorsum. The body wall is thicker and less transparent than in C. longipedunculatus . The inner surface is uneven, raised in places into low, cushion-like elevations filled with sparse, opaque yellowish granules. Body muscles form a regular network with more or less rectangular meshes. The circular muscles are crowded around the siphons. Branchial tentacles number about 18, the dorsal ones appreciably larger than the others. The middorsal tentacle reaches the bottom of the branchial sac. The prepharyngeal band, just behind the ring of tentacles, makes a wide but shallow dorsal V around the almost flat and inconspicuous dorsal tubercle. The branchial sac has six well-defined folds with wide flat intervals between them. The branchial formula is: 6(4)2(6)3(7)3(7)3(8)3(7)2DL2(8)3(6) 3(5)5(6)4(7)3(6)3. Three gonads each of four or five lobes are on each side of the body. On the left side one gonad is inside the gut loop; on the right, the three gonads are close and parallel, forming a compact group. The anal margin is undivided. A cluster of large zooids of Hydrozoa of the family Calycopsidae (identified by Dr. O. Sheiko) was found in the branchial sac, one was attached to a branchial tentacle. Remarks The specimens described by Vinogradova (1970) (Kurile-Kamchatka Trench) and Sanamyan and Sanamyan (1998) (Aleutian Trench) have abundant spicules in all tissues, while the present specimen lacks spicules confirming that this feature cannot be used as a species-specific character. According to Vinogradova (1970) , C. tenuis is abundant in the Kurile-Kamchatka Trench, 40 specimens of this species being found at six stations at 5035–6282 m . Sanamyan and Sanamyan (1998) recorded a larger (body length 10 cm ) specimen in the western point of the Aleutian Trench, 6074– 5300 m . Despite its larger size the latter specimen had the same number of gonads (two on the left, and three on the right) and each gonad has the same number of lobes. The distribution of the gonads is also similar, two left gonads being above and one inside the gut loop. This species was regarded as a probable synonym of C. sluiteri Ritter, 1913 (see Monniot and Monniot 1991 , p 421), but they certainly are not conspecific. Culeolus sluiteri has large papillae on the test and a different postero-ventral crest. The number of gonads is similar, C. sluiteri having three gonads on the right and one on the left, the latter inside the gut loop. Ritter (1913) stated that the presence of only five branchial folds is one of the significant distinguishing features of his species. The number of the branchial folds appears to be relatively stable in Culeolus (the other species which consistently has five folds is C. anonymus ). Another related species, C. nadejdae Sanamyan, 1992 , has up to five gonads on the left, all of which, unlike C. tenuis , are in the gut loop. Culeolus nadejdae appears to be more closely related to C. sluiteri than to C. tenuis ; differing from C. sluiteri only in the number of gonads in the gut loop, and in having six branchial folds.