Bathystyeloides enderbyanus ( Michaelsen, 1904 )

Sanamyan, K. E. & Sanamyan, N. P., 2006, Deep-water ascidians (Tunicata: Ascidiacea) from the northern and western Pacific, Journal of Natural History 40 (5 - 6), pp. 307-344 : 310-314

Bathystyeloides enderbyanus ( Michaelsen, 1904)

( Figures 1 , 2A )

Bathyoncus enderbyanus Michaelsen 1904, p 226 ; Kott 1969, p 125.

Bathystyeloides enderbyanus: Millar 1959, p 197 ; 1970, p 131; Monniot and Monniot 1970, p 323 (part); 1973, p 443; 1974, p 756; 1976, p 669; 1977, p 313; 1985a, p 29; 1985b, p 292; 1985c, p 39; 1987, p 38; 1988, p 406; 1994, p 28; Monniot 1994, p 235; 1997, p 20.

? Bathystyeloides anfractus: Monniot and Monniot 1985c, p 39 ; Sanamyan and Sanamyan 1999, p 1854.

Bathystyeloides atlantica Millar 1955, p 229 .

Bathystyeloides magnus Sanamyan and Sanamyan 1999, p 1855 .

Material examined

St. 6117, 3350– 3370 m, one specimen; St. 7168, 7440– 7450 m, 15 specimens; St. 7206, 7880– 7420 m, one specimen.

Description

The specimen from St. 6117 has a spherical body (8 mm diameter) with sparse, short, test hairs ventrally and a few on the sides. About 20 flat triangular tentacles are on a high branchial velum. The circular prepharyngeal band lacks any dorsal indentation and is closer to the branchial velum dorsally than ventrally. The neural ganglion is well separated from the small, round dorsal tubercle. The branchial sac has 60–75 longitudinal vessels on each side. A deep inverted fold between the dorsal lamina and the first dorsal longitudinal vessel displayed by severing the short connectives between the dorsal vessel and dorsal lamina has eight well-defined transverse rows of up to 15 longitudinal stigmata per row. The remainder of the branchial sac has only long transverse stigmata characteristic of the genus. One long immature gonad is on each side of the body. Small testis follicles are in two rows beneath the ovary. Three or four endocarps are in an unequal line on each side of the body. The stomach has eight or nine well-marked folds and a small caecum. The anal margin has about 15 distinct lobes.

Specimens from St. 7168 and St. 7206 are smaller (about 4.5 mm diameter) and differ in having significantly longer ventral test hairs (several times longer than the body), the prepharyngeal band an equal distance from the branchial velum all around, gonads smaller with few large male follicles, and ova and only one endocarp on each side of the body (ventral side to the gonad). The branchial sac is as described above, but has fewer longitudinal vessels (about 50 on each side), and the distance between the dorsal tubercle and the ganglion is variable (see Figure 1B, C ).

Remarks

Bathystyeloides enderbyanus is a widely distributed, probably cosmopolitan, and an often recorded abyssal species. Although longitudinal stigmata were not reported for this species before, we believe they were overlooked by previous workers. These stigmata which are hidden in the inverted fold are not visible from the inner side of the branchial sac. We found longitudinal stigmata in every Bathystyeloides species examined (including numerous specimens from the Tasman Sea and from the region between Australia and Antarctica, the specimen from southwest Africa, and the present specimens from north and west Pacific). Bathystyeloides magnus Sanamyan and Sanamyan, 1999 , distinguished from B. enderbyanus only by the presence of longitudinal stigmata, appears to be a junior synonym of the present species, its other characters, including the widely separated neural ganglion and dorsal tubercle and the relatively long gonads, being identical in the two taxa. Bathystyeloides anfractus Monniot and Monniot, 1985 also may be a synonym, differing from B. enderbyanus in the relative position of the ganglion and dorsal tubercle, a variable feature in Bathystyeloides that may depend on the size of the body.

The present record from 7440 m is the deepest record for Styelidae .

Cnemidocarpa barbata Vinogradova, 1962

( Figure 2B, C )

Cnemidocarpa barbata Vinogradova 1962, p 202 ; Monniot 1978, p 189; Kott 1990, p 268.

Material examined

St. 6109, 3460 m, one specimen; St. 6111, 2880 m, four specimens; St. 6117, 3350– 3370 m, three specimens.

Description

The oval upright specimens are 7–10 mm high. Apertures are on the upper surface, slightly protruding in one specimen ( Figure 2B ), but sessile in the other. Much-branched test hairs are on the posterior end of the body, but otherwise the test is free from hairs or foreign particles and is covered by crowded minute papillae (similar to those on Cnemidocarpa bythia ( Herdman, 1881)) . The test is thin and very difficult to separate from the body in alcohol-preserved specimens. The body musculature consists of thin but continuous layers of circular and longitudinal muscles.

About 20 large and a number of small branchial tentacles arise from a low branchial velum. A low atrial velum with a ring of atrial tentacles surrounds the inside opening of the atrial siphon. Sparse tentacle-like papillae are on the test lining inside of the atrial siphon. The prepharyngeal band composed of two lamellae, the anterior of which, about 0.3 mm high, is well separated from the branchial velum. The three poorly defined branchial folds have internal longitudinal vessels arranged more or less as in the following formulae from two of the newly recorded specimens: E5(14)(18)(12)4DL(14)6(19)4(9)7E and E10(11)15(10)10(17)12DL23(16)(16)18(11)11E. Several of the internal longitudinal vessels adjacent to the plain-edged dorsal lamina on the right side are significantly higher than the others. The dorsal lamina is removed from the closest longitudinal branchial vessel on the right, and transverse vessels connecting this vessel and the dorsal lamina are raised into laminar expansions.

One long Cnemidocarpa - type gonad is on each side of the body. In one specimen the left gonad is parallel and close to the gut loop and rectum ( Figure 2C ), in another it lies halfway between the gut and branchial siphon. Large male follicles are in two more or less regular lines between the ovary and the body wall along the whole length of the ovary projecting slightly from the sides of the ovary. The oviduct is short, and male and female openings are close to each other. The gut forms a simple short loop loosely attached to the body wall. The large globular stomach has about 20 well-defined longitudinal folds but a caecum was not detected. The anal margin has about 10 distinct rounded lobes. Five to eight large to medium-sized endocarps are on each side of the body, mainly around the gonads, and one is in the gut loop.

Remarks

Originally described from the Indian sector of Antarctica at 639 m ( Vinogradova 1962), the species subsequently was recorded from the Kerguelen shelf ( Monniot 1978) and from New South Wales ( Australia) at 1200 m ( Kott 1990). The present record from the northern Pacific is far from the previously recorded range and at a greater depth. However, we failed to find any reliable characters that could separate northern Pacific from the southern hemisphere specimens, apart from the atrial tentacles and the papillae on the whole inner surface of the atrial siphon. Such papillae are present in several deep-water Styelidae , for instance in Cnemidocarpa bythia (see Sanamyan and Sanamyan 2002, 2005), but they can usually be observed only after staining. They may be easily overlooked if the inner side of the atrial siphon is removed with the rest of the test. Externally, the present specimens look exactly as in the photograph of Monniot (1978, Figure 3C ). Internally an outstanding character of this species is the relatively high anterior lamella of the prepharyngeal band (similar in north Pacific and Kerguelen specimens) which is higher than in other deepwater styelids. Kott (1990) noted some variations in the number of anal lobes, but she may have based that assessment on incorrect translation of the original Russian description; according to Vinogradova (1962) the anal margin has 15 small lobes (but is not bilabiate).

The newly recorded specimens are from greater depths than those previously reported for this species.

Figures

Figure 1. Bathystyeloides enderbyanus (Michaelsen, 1904). Specimens opened along ventral mid line; branchial sac removed. (A) Specimen from St. 6117; (B, C) specimens from St. 7168.

Figure 2. (A) Bathystyeloides enderbyanus (Michaelsen, 1904), intact specimen from St. 7168. (B, C) Cnemidocarpa barbata Vinogradova, 1962: (B) intact specimen; (C) specimen opened along ventral mid line; branchial sac removed.

Figure 3. Styela hadalis sp. nov. (A) Specimen opened along ventral mid line; branchial sac removed; (B) gut loop and distal part of the left gonad; (C) branchial velum, prepharyngeal band, dorsal tubercle, and ganglion; (D) ring of atrial papillae.