Diplosoma pannosum, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 277-278

Diplosoma pannosum n. sp.

( Figs 61 ; 121E )

TYPE MATERIAL. — Philippines. Cebu Straits, Cabilao Island, cave, 9°53.39’N, 123°45.45’E, 10 m, 15.IV.1997 ( MNHN A 2 DIP. A 145).

ETYMOLOGY. — From the Latin pannosus: in rags.

OTHER MATERIAL EXAMINED. — Philippines. Cebu, E Mactan Island, overhang, 10°15.47’N, 123°59.08’E, 30 m, 14.IV.1997 (MNHN A2 DIP.A 146).

DESCRIPTION

The colonies, 20 to 30 cm across and 5 to 10 mm thick, are encrusting. Inflated underwater, the living colonies are billowy, brown and translucent, with darker patches surrounded by clear spots corresponding to the zooids’ apertures ( Fig. 121E ). When removed from the substrate they tear to shreds (giving the species its name), and they lose their shape. Large, tubular common cloacal siphons have a transparent tunic.

The zooids are gathered in groups in gelatinous cores of tunic separated by wide channels. The superficial and basal sheets of tunic have a firmer consistency than intermediate levels. Brown pigment cells are scattered throughout the tunic, but more abundant around the zooids. The body wall of the zooids is devoid of pigment, but some is present in the larvae. The thoraces are elongated with a narrow oral siphon fringed by six small lobes ( Fig. 61A ). The cloacal aperture is large. The branchial stigmata could not be counted. The retractor muscle is absent and the waist is short. The abdomen ( Fig. 61B, C ) is folded under the thorax, and the single-lobed testis protrudes below the gut loop. The sperm duct arises from the posterior part of the testis, passes over it and then follows the rectum. Its proximal part is inflated ( Fig. 61B, C ). The oocytes develop in a pouch protruding from the abdominal body wall. The larvae ( Fig. 61D ) develop in the basal layer of the colony. They are oval with a tail equal in length to the trunk. The three short, stout adhesive papillae are encircled by about 20 clear ampullae that have dense tips. The sensory vesicles lie in a protrusion of the larval thorax where four rows of stigmata already appear. A bud grows on each side of the larva. The larva measures 1.25 mm.

REMARKS

Among the Diplosoma species with a single testis follicle, D. pannosum n. sp. differs from Diplosoma ata Monniot C. & Monniot F., 1987 in the absence of retractor muscle and more numerous larval ampullae. It differs from Diplosoma redika Monniot F., 1994 in its larval structure.

Diplosoma handi Eldredge, 1967 , from the Caroline Islands, is described as making colonies with a tough, thick, solid tunic, containing symbiotic algae in cloacal channels, and having zooids with a retractor muscle.

Diplosoma hiatti Eldregde, 1967 , from Eniwetok, has zooids with a retractor muscle; the zooids are arranged around a single common cloacal aperture per colony.

Figures

FIG. 61. — Diplosoma pannosum n. sp.; A, thorax; B, C, abdomen; D, larva. Scale bar: 0.5 mm.

FIG. 121. — A, Polysyncraton aspiculatum Tokioka, 1949; B, Polysyncraton cerebellum n. sp.; C, Polysyncraton thallomorpha Monniot F., 1993;D, Diplosoma marsupiale n. sp.; E, Diplosoma pannosum n. sp.; F, Diplosoma pavonia Monniot C. & Monniot F., 1987.