Polyandrocarpa polypora, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 320-322

Polyandrocarpa polypora n. sp.

( Figs 90 ; 127F)

TYPE MATERIAL. — Fiji. Viti Levu, Beqa Passage, Shark Reef, crevice 20 m, 18°16.48’S, 178°00.27’E, 19.X.1996 ( MNHN S1 POL.A 43).

ETYMOLOGY. — From the Greek poly: numerous and poros: hole.

OTHER MATERIAL EXAMINED. — Tonga. Vava’u, Swallow Cave, NW end of Kapa Island, on rock wall, 18°40.93’S, 174°02.85’W, 10 m, 8.XI.1997 (MNHN S1 POL.A 44). — W Tongatapu, on reef, 27 m, 21°03.83’S, 175°19.98’W, 10 m, 18.XI.1997 (MNHN S1 POL.A 45).

DESCRIPTION

This species forms globular colonies that reach 6 cm across, on peduncles 2 to 3 cm thick and 6 cm high. The siphons are oval or circular in life. They are light beige exteriorly and white interiorly. The colony is naked; the sand particles in the photo (Fig. 127F) do not adhere to the tunic. When preserved in formalin the colony becomes entirely black. The siphons are placed without special order in the colony (hence the species name). In each zooid they are at least 1 cm apart. When two siphons are close together, they belong to two different zooids.

The contracted zooids measure at least 1.5 cm. They are enclosed in a tunic capsule and are linked to the common tunic by several blood sinuses. The capsules are hollowed out entirely within the common tunic; to reach the colony surface the oral siphon is 3 to 5 mm long and the cloacal siphon 5 to 7 mm long. The centre of the colony and the peduncle are filled with a black tunic that is both fibrous and gelatinous, crossed by blood sinuses. Among the zooids there are some closed cavities containing cell masses that we interpret as degenerated zooids. No bud was found.The body wall is opaque.Its external layer contains the muscles, its thick internal layer contains clear vesicles. The oral tentacles number about 20 in two or three orders of size, inserted at the base of the long oral siphon, close to the branchial sac. They are curved internally in contracted specimens. The prepharyngeal band has a single thick crest and is deeply indented dorsally.

The dorsal tubercle opens by a simple hole in the middle of protruding tissue that contains numerous granules. The dorsal lamina is low, its height only increasing at its mid-length.

The branchial sac has four folds on each side; R.E. 8 6 3 6 2 7 2 8 1–0 D.L. 0 8 3 7 3 6 3 6 7 E.L. In the anterior and middle parts of the branchial sac, the first vessel on the right side is equidistant between the dorsal lamina and the first fold. Posteriorly it parts from the dorsal lamina and draws nearer to the first fold. The longitudinal vessels are high.The branchial meshes contain an average of six stigmata between the folds and two to four on the folds. In the ventral part of the branchial sac, the stigmata are usually cut by parastigmatic vessels. The transverse vessels contain numerous muscular fibres. The gut ( Fig. 90A ), a closed loop, lies very posterior. The stomach is wide with obvious folds. There is no true caecum but rather just a small button in its place. The irregular intestine ends near the cloacal siphon by an indented anus with a rolled rim. The gonads ( Fig. 90A, B ) are included in the internal layer of the body wall and covered by a continuous layer of clear granules. They are composed of a central ovary encircled by a crown of round testes. The central part of the ovary is in contact with the external layer of the body wall ( Fig. 90C ). The testis lobes send out sperm ducts, which join to form a papilla opening far from the oviduct ( Fig. 90B ). In one of the polycarps we have found two papillae joined by a channel.

In the most mature colony the polycarps were scattered without order on the whole internal side of the body wall ( Fig. 90A ). We counted about 15 on each side, some of them very small and at the beginning of their development. In other colonies we have found less than 10 polycarps, mostly developed on the ventral side; in some cases they seem to lie in a line.

In one young specimen we found incompletely developed polycarps comprising an oviduct and one or two testis lobes, but these rudiments were few. It may be possible that new polycarps keep appearing during the growth of the zooid.

There is a single endocarp in the intestinal loop ( Fig. 90A ). We have not found cloacal tentacles; in their place is a circle of mere protruding buttons.

REMARKS

This species is unique among Polyandrocarpa in forming a colony with a well-defined form, including a differentiated peduncle, a rare structure among stolidobranchs, comparable only to the South African species Gynandrocarpa lacerta ( Herdman, 1886) (see Monniot C. et al. in press). Another Polyandrocarpa , P. watsonia Kott, 1985 , has a different form: “The colony forms a thick, curved upright lamella, slightly convex on one side and concave on the other, with a long, curved upper outer border and a shorter basal edge by which it is fixed” ( Kott 1985: 225). The zooid of P. watsonia is very different from that of P. polypora . As suggested by Kott (1985), the genus Polyandrocarpa is certainly polyphyletic. It artificially groups disparate species and cladistic lineages encountered in the genus Polycarpa . These include particularly species having endocarps scattered around the gonads, species without any endocarps, and, as with P. polypora , species with a single endocarp in the gut loop and gonads included in the body wall and covered with vesicles. This last lineage of Polycarpa is mostly diversified in the Indo-Pacific region.

Figures

FIG. 90. — Polyandrocarpa polypora n. sp.; A, specimen ventrally opened; B, C, both sides of a polycarp. Scale bars: A, 5 mm; B, C, 0.5 mm.