Stolonica bigyna, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 317-318

Stolonica bigyna n. sp.

( Figs 88 ; 127D)

TYPE MATERIAL. — Fiji. Lau Group, Weilagilala Atoll, lagoon channel, 16°46.48’S, 179°07.46’E, 10 m, 30.IX.1996 ( MNHN S1 STO 20).

ETYMOLOGY. — From the Greek gune: woman.

DESCRIPTION

This species makes plates of closely packed zooids that are separated from their base. The colour is a deep red (Fig. 127D). Each siphon has six white spots. The colour, essentially concentrated in the tunic, fades in formalin preservative. The zooid’s body wall is yellowish. The zooids are linked by stolons. There is some weakly attached sand on the tunic. The tunic is thin and contains large clear vesicles. The musculature is thin and regular.

There are 12 large, stout oral tentacles of two orders. The prepharyngeal band has a single thick crest. The dorsal curve is not deep. The protruding dorsal tubercle opens in an antero-posterior slit. The dorsal lamina is high with a double crest. The branchial sac has three folds on each side. The formula is:

R.E. 5 7 .3. 7 3 7 1 to 5 D.L. 0 7 4 8 2 7 3 E.L.

The longitudinal vessels between folds one and two on each side are slightly higher, but, in contrast to other species of this genus, there is not a double-sized vessel, which would represent a second, regressed fold. Several vessels are intercalat- ed in the widened space between the first fold on the right side and the dorsal lamina; they generally begin close to the dorsal lamina, but sometimes lie close to the first fold. The branchial meshes are long and contain three to four stigmata between folds, cut by a parastigmatic vessel. We counted generally two stigmata per mesh on the folds. On each side of the dorsal lamina, the meshes may contain six to seven stigmata.

The stomach has 21 distinct folds interrupted at the level of the typhlosole ( Fig. 88B, C ). The caecum is hook-shaped. The pyloric gland is clearly visible on the whole enlarged part of the intestine. The pyloric channel is independent from the caecum. The slightly enlarged anus has a smooth rim.

The gonads lie along a line on each side of the endostyle in the posterior half of the body ( Fig. 88A ). There are eight to ten testes per side, spherical or slightly lobed, each with a very long sperm duct. An ovary is coupled to each testis on the left side, and coupled to two to four testes on the right side in the middle of the row. Most of the ovaries on the left are well-developed ( Fig. 88D ); this is not the case on the right side, but in all the specimens studied there are at least rudimentary ovaries. The ovaries contain numerous oocytes, the smallest of which are ventral. The specimens in this collection had not reached complete sexual maturity and were not incubatory. Endocarps are scattered on the body wall. The base of the cloacal siphon is encircled by small tentacles.

REMARKS

The genus Stolonica Hartmeyer, 1903 s.s. seems very homogeneous, with a branchial sac reduced to three complete folds and hermaphroditic gonads comprising a massive ovary and a single testis opening by a long sperm duct. The male or hermaphroditic gonads of the closely related genera Amphicarpa and Distomus have a very different aspect. Until now, there has not been any Stolonica species described with hermaphroditic gonads on the left side. The disposition of hermaphroditic and female gonads has been the most reliable character to distinguish the genera Stolonica (ovaries on the right) and Amphicarpa (ovaries on both sides). Our new species possesses ovaries on both sides, but all other characters closely ally it to the other Stolonica species. S. bigyna n. sp. in life has exactly the same appearance as the Coral Sea species Stolonica variata Monniot C., Monniot F. & Laboute P. (1991: 212) , but the two species differ in the elongate and lobed testes and the ovaries with few oocytes in S. variata .

Figures

FIG. 88. — Stolonica bigyna n. sp.; A, specimen opened along the ventral side; B, C, both sides of the stomach; D, gonads. Scale bars: A, 2 mm; B, C, 1 mm; D, 0.5 mm.