Styela multitentaculata, Sanamyan & Sanamyan, 2006

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 : 317-326

Styela multitentaculata sp. nov.

( Figures 4B , 5 )

Material examined

St. 6089, 170 m, one specimen. Holotype KIE 1/1133.

Description

A small dome-shaped specimen (about 5 mm high and 6 mm diameter at the base) is firmly fixed to a small stone by a wide flat ventral surface. The cloudy, translucent, thin but firm test spreads into a short membrane around the area of attachment. It has no hair-like outgrows and the surface is smooth and clear, without foreign particles. Small sessile apertures are close to each other, the branchial aperture terminal and the atrial aperture slightly displaced dorsally.

The body wall is thin, almost transparent and contains sparse stellate spicules about 0.02 mm in diameter. The muscles are weak and form a thin continuous layer. The branchial velum is wide but low. About 25 crowded branchial tentacles, short and rather thick, especially at their bases. The prepharyngeal band is a single lamella that runs close to the ring of tentacles and lacks a dorsal V. The large round dorsal tubercle has a simple transverse slit. The large oval neural ganglion is posterior and close to the dorsal tubercle halfway between the siphons. The high dorsal lamina has an uneven, slightly toothed margin ( Figure 5C ). The branchial sac has four pronounced folds with closely set inner longitudinal vessels. The interspaces between the folds are narrow and contain no more than two inner longitudinal vessels and it is difficult to decide if these vessels are in the interspaces or belong to the adjacent folds. The branchial formula is: 1(11)2(12)2(9)2(13)2DL0(9)2(6)2(11)0(11)0.

The gut forms a simple, narrow U-shaped loop. The oesophagus is relatively long and curved. The short, rectangular stomach has 16 well-defined longitudinal folds and a long curved caecum. The long intestine ends in an anus with the rim divided into several distinct lobes. Gonads are well developed, one on each side of the body. Ovaries are thick deeply undulating tubes of moderate length, ending in short oviducts in a distance from the atrial orifice. Numerous large, deeply subdivided male follicles form a compact voluminous mass behind the proximal end of the ovary. As seen from the outside ( Figure 5B ), the male follicles are completely posterior to the ovary and do not overlap it. They join to single thick duct running between the male gonad and body wall and then along the mesial surface of the ovary. The male opening is almost sessile, on a short inconspicuous papilla near the oviductal opening. One large and several smaller endocarps are on each side of the body but not in the gut loop. The atrial tentacles are peculiar: they are unusually long (longer than the branchial tentacles), filiform and extremely numerous, arranged in a perfect circle around the atrial aperture and are crowded on two anterior lamellar expansions of the body wall, on the sides of the neural ganglion ( Figure 5D ).

Remarks

The present species has some resemblance to the small hemispherical specimens identified (by Lutzen 1959) as young specimens of Styela gelatinosa Traustedt, 1886 . Individuals of Styela gelatinosa , however, are large reaching 84 mm high. The present specimen, 5 mm high, with its voluminous mature gonads, cannot be a young specimen of S. gelatinosa . Another similar species, S. squamosa Herdman, 1881 (described below), is also significantly larger than S. multitentaculata sp. nov., has the plain-edged dorsal lamina, and its male follicles are spread around or overlap the posterior end of the ovary rather than forming the compact mass behind the ovary as in the present species. Styela coriacea (Alder and Hancock, 1848) has a similar body shape, but the gonads are different, the male follicles being distributed along the side of the ovary.

Styela multitentaculata sp. nov. has significantly longer and more numerous atrial tentacles than the other ascidians we have the opportunity to examine. The stellate spicules in the body wall also may be characteristic of the species rather than an artefact of fixation as they are not present in the other ascidians from the same station kept for many years in the same bottle. This, however, needs to be confirmed on more material.

Styela sigma Hartmeyer, 1906

( Figure 6 )

Styela sigma Hartmeyer 1906, p 12 ; Nishikawa 1991, p 123; Sanamyan 2000, p 70.

Not Styela sigma Monniot and Monniot 2003, p 715 .

Styela atlantica: Tokioka 1953, p 264 ; 1967, p 191; Tokioka and Nishikawa 1977, p 23.

Material examined

St. 6132, 1100– 830 m, one specimen.

Description

The specimen, about 1.5 cm diameter, is attached by the wide ventral surface to a hexactinellid sponge. The apertures are close together on the upper surface, on short diverging siphons. The test is hard and rigid, opaque, roughly wrinkled and has firmly attached, fine, sparse sand grains. About 25 short tentacles of two size orders are on a low branchial velum. The prepharyngeal band has a shallow dorsal V around the large dorsal tubercle, which has a U-shaped slit. The high dorsal lamina is plain edged. The branchial sac has four prominent folds. The branchial formula is: 4(8)7(13)3(14)3(18)4DL3(10) 6(13)4(13)4(7)3.

The gut forms a narrow, almost straight loop with a large voluminous stomach, thick intestine and long rectum. The stomach has about 20 conspicuous internal longitudinal folds and a small caecum. The anal margin has a number of small rounded lobes.

Two gonads are present on each side of the body. The ovaries are long and thick, their distal halves converging. On the left side the anterior ovary almost reaches mid-ventral line above the pole of the gut loop, the ventral (proximal) end of the posterior ovary (which is less than half the length) is in the middle of the secondary gut loop. On the right, both have their proximal ends against the thick tubular heart. Small, pear-shaped male follicles are in bunches around and some distance from the proximal halves of the ovaries. Many mediumsized endocarps are spread over the inner body wall. Numerous atrial tentacles form a wide band encircling the atrial siphon and are crowded on two anterior lamellar expansions of the body ( Figure 6B ).

Remarks

We follow Nishikawa (1991) in referring at least Pacific records of S. atlantica (Van Name, 1912) to this species. The large specimen from the Philippines described by Monniot and Monniot (2003) has a very long rectum and differs from all other Pacific specimens (see synonymy) in the relative length of the ascending and descending limbs of the gut loop. The male part of the gonad, consisting of a few entire male follicles arranged in a row around the proximal end of each ovary, also differs from north Pacific specimens. The Philippine specimen belongs to another species. The other records of this species include Japan, East Kamchatka, and the Aleutian Islands.

Styela squamosa Herdman, 1881

( Figures 7–9 )

Styela squamosa Herdman 1881, p 66 ; Monniot and Monniot 1982, p 113; 1983, p 77; 1994, p 33; 2003, p 717; Monniot 1993, p 356; Millar 1988, p 1430.

Styela oblonga Herdman 1881, p 65 .

Tethyum tholiforme Sluiter 1912, p 455 .

Styela milleri Ritter 1907, p 21 ; Van Name 1945, p 308; Millar 1964, p 62; 1969, p 91.

Styela gracilocarpa Millar 1982, p 80 .

Styela maculata Sanamyan 1992, p 192 .

Material examined

St. 6142, 5000– 4990 m, one specimen; St. 2323, 4890–4984, one specimen.

Description

Upright, cylindrical, or oval specimens, the largest (St. 6142) 3 cm high and 1.5 cm diameter, firmly attached to small stones by the whole basal surface and with a tuft of rhizoids spreading over the stone. The test is hard and thin and its surface is warty, densely wrinkled and dirty grey-brown. Two small inconspicuous sessile apertures are on opposite ends of the upper surface.

The body wall is thick and muscular. About 30 thick and long branchial tentacles are on a low velum. The prepharyngeal band is a single thick lamella and has a V-shaped notch around the round dorsal tubercle, which is halfway between the siphons and has a Ushaped slit. The large neural ganglion is close to the dorsal tubercle, displaced slightly to the left. Extending from it are a pair of branched anterior nerves, and a pair of unusually thick posterior nerves running to the atrial siphon. The high dorsal lamina has a plain, but folded margin. The branchial sac is thick and has four low folds and crowded internal longitudinal vessels. The branchial formula for the largest specimen is: 4(10)7(17)7(18)6(20) 2DL4(15)4(20)7(11)10(8)2. Stigmata are long and often are crossed by parastigmatic vessels. Up to nine stigmata per mesh are between the folds, but in most places are fewer, and on the folds the longitudinal vessels are set very close to each other.

The small stomach has about 20 distinct longitudinal folds and a small caecum. The shape of the gut loop is slightly different in the two specimens and probably depends on the shape of the body. The larger specimen (St. 6142, Figure 8 ) has an almost straight, vertical, narrow J-shaped loop and an almost straight intestine, the smaller specimen (St. 2323, Figure 9A ) has a narrow, closed primary loop and widely opened secondary loop. The anal opening, bordered by many small lobes, is just below the atrial orifice.

One long gonad is on each side of the body; the left is almost straight and the right with its the posterior end turned slightly ventrally. Numerous small male follicles form a compact mass around the posterior end of each ovary. Many medium-sized endocarps are spread over the inner body wall. Numerous thin and short atrial tentacles are on a short velum with two prominent anterior horns ( Figure 8A ).

Remarks

Monniot and Monniot (1982, 1983) re-examined types of S. squamosa , S. oblonga , and Tethyum tholiforme and synonymized these species. Although S. oblonga has page priority, S. squamosa was chosen as the valid name.

Monniot (1993) listed S. milleri and S. gracilocarpa as probable synonyms of S. squamosa and this opinion is adopted here. According to the original description, S. milleri has 18 or 20 longitudinal vessels on each face of the largest folds, giving 36–40 vessels per fold ( Ritter 1907). This number is twice that in all other recorded specimens and it is likely that the specimen had 18–20 vessels on the entire fold (rather than on each face). Millar (1982, p 80) distinguished his S. gracilocarpa (with 20 longitudinal vessels on the largest fold) from S. milleri only by ‘‘many fewer longitudinal branchial bars in animals of similar size’’, although previously he ( Millar 1959) identified a specimen having only 11 vessels as S. milleri . An abnormal specimen with numerous male openings recorded by Millar (1964) as S. milleri also certainly belongs to S. squamata . We examined the similar specimen from New Zealand (at 1600 m), and found a single male opening on the left gonad, but four male papillae on the right.

The specimens described as S. maculata by Sanamyan (1992) are similar to the present specimens, but have slightly different gonads: the male follicles are attached to the body wall some distance from the ovary ( Figure 9B ). Although all known specimens of S. maculata (nine specimens from the Sea of Okhotsk, 1500 m) have the same gonads, suggesting the stability of this feature, it hardly seems a sufficient character to distinguish the two species and S. maculata is synonymized here with S. squamosa .

These are the greatest depths so far recorded for the species.

Styela tenuibranchia Monniot, Monniot and Millar, 1976

( Figure 10 )

Styela tenuibranchia Monniot et al. 1976, p 1193 ; Monniot and Monniot 1985b, p 297; Sanamyan and Sanamyan 1999, p 1850.

Material examined

St. 6109, 3460 m, five specimens; St. 6117, 3350– 4990 m, one damaged specimen.

Description

Oval specimens 5–8 mm diameter, all of similar appearance. The body is covered with short, not very crowded hairs with a naked area only around and between the siphons. The hairs may be sparser laterally and ventrally. Sparse minute sand grains are attached to the test and its hairs. About 14 short, flattened branchial tentacles are present. The prepharyngeal band makes a circular line without a dorsal indentation. The branchial sac is flat, without any trace of folds. The number of the internal longitudinal vessels on each side appears to be about 50–60 (although in the preserved specimens the right and left sides of the branchial sac adhered strongly to each other and obscured the exact number of vessels). The shape and position of the gonads and endocarps, the gut loop with the short folded stomach and conspicuous caecum, and a smooth anus ( Figure 10B ) are as described for the specimens from the Coral Sea ( Sanamyan and Sanamyan 1999).

Remarks

The present record of this species from the Gulf of Alaska is far from all the previous records (Indian Ocean near Sri Lanka, Tasman Sea, and Coral Sea). The present specimens are smaller and have less numerous longitudinal branchial vessels than recorded for southern hemisphere specimens, Monniot et al. (1976) recorded more than 100 and Sanamyan and Sanamyan (1999) recorded 95–100 vessels on each side of the branchial sac.

Bathypera oIJoida ( Ritter, 1907)

Halomolgula oυoida Ritter 1907, p 3.

Bathypera oυoida: Van Name 1945, p 369; Nishikawa 1981, p 187; Sanamyan 1992, p 188; 1996, p 205; Monniot 1998, p 552.

Material examined

St. 6132, 1100– 830 m, one specimen.

Remarks

This easily recognizable species has a wide range in the North Pacific. Monniot (1998) erroneously reported the species from 40 ° 45.59S , the correct locality is 40 ° 45.59N.

Figures

Figure 4. (A) Styela hadalis sp. nov.; (B) Styela multitentaculata sp. nov. External view.

Figure 5. Styela multitentaculata sp. nov. (A) Specimen opened along ventral mid line; branchial sac removed; (B) proximal part of the right gonad, external view through the transparent body wall (male follicles and the proximal end of the ovary); (C) part of the dorsal lamina; (D) internal view of the dorsal area (branchial and atrial tentacles, prepharyngeal groove, dorsal tubercle, and ganglion).

Figure 6. Styela sigma Hartmeyer, 1906. (A) External view; (B) specimen opened along ventral mid line; branchial sac removed.

Figure 7. Styela squamosa Herdman, 1881. Specimen from St. 2323, external view.

Figure 8. Styela squamosa Herdman, 1881. Specimen from St. 6142. (A) Internal view of the intersiphonal area (branchial and atrial tentacles, prepharyngeal groove, dorsal tubercle and neural ganglion); (B) specimen opened along ventral mid line; branchial sac removed; (C) proximal part of the right gonad.

Figure 9. Styela squamosa Herdman, 1881, specimens opened along ventral mid line; branchial sac removed. (A) Specimen from St. 2323; (B) paratype of S. maculata Sanamyan, 1992.

Figure 10. Styela tenuibranchia Monniot et al., 1976. (A) Intact specimen; (B) specimen opened along ventral mid line; branchial sac removed.