Diazona textura Monniot C., 1987

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 293-294

Diazona textura Monniot C., 1987

( Figs 74 ; 124B )

Diazona textura Monniot C., 1987a: 4 , fig. 1. Type locality: New Caledonia. — Monniot C. & Monniot F. 1991: 379, fig. 14, New Caledonia.

MATERIAL EXAMINED. — Federated States of Micronesia. Chuuk Lagoon outer reef, oceanside Onang Island, 7°13.46’N, 151°37.78’E, 40 m, 18.III.1992 ( MNHN P1 DIA 38).

DESCRIPTION

In life this species looks like D. tenera , in that it has the same transparency with white pigment stripes ( Fig. 124B ). But here the endostyle is a neat line. The prepharyngeal band and some of the transverse vessels have a less obvious pigmentation. The siphons have six white spots. The diffuse white colour of the branchial sac in D. tenera is absent in D. textura .

The colonies are in the shape of cushions. Each zooid protrudes slightly at the colony surface, which is free of epibionts. When fixed, the tunic is soft and transparent with some thin and poorly ramified sinuses. The thoraces are perpendicular to the colony surface and reach 1 cm when relaxed. The abdomens are as long as the thoraces. According to the colony thickness, the abdomens are in the long axis of the thoraces or else lying against the lower colony surface. The oesophago-rectal peduncle takes half of the total length of the abdomen. We have not seen any vascular post-abdominal process.

The musculature is characteristic ( Fig. 74A ). It is mainly constituted of transverse fibres extending from the endostyle to the dorsal lamina, gathered in the median part of the thoracic wall into a reduced number of bundles. The musculature issuing from the siphons does not extend beyond the anterior third of the thorax; fibres coming from the ventral posterior half of the thorax make the muscular bundles running down the abdomen. These bundles end in two anchoring masses on the left side at the base of the abdomen. The siphons have six lobes. The long and curved oral tentacles have joined bases and are planted anteriorly in the oral siphon. The prepharyngeal band is made of a single blade; it forms a deep dorsal V. The dorsal tubercle is an antero-posterior slit ( Fig. 74B ). The round neural ganglion is close to the dorsal tubercle. The neural gland forms radiating lobes ( Fig. 74B ). The dorsal lamina has sharp languets clearly displaced to the left side. There is a large unperforated space on the right side of the dorsal lamina.

The branchial sac has about 35 rows of stigmata and 20 to 25 longitudinal vessels on each side. There is a line of T-shaped papillae on each side of the dorsal lamina. The meshes are elongated and contain three stigmata.

The stomach is elongate with numerous internal folds. The gonads were not developed in the zooids of this collection.

REMARKS

The specimens dredged previously in the south of New Caledonia were not in as good condition as the Chuuk specimens. The musculature in the former is mainly transverse and less developed dorsally than in the present collection, but all other characters are identical.

D. textura is easily distinguished from all the Diazona from the western Pacific. The only other species with a mainly transverse musculature is Diazona labyrynthea Monniot F. & Monniot C., 1996 , which has a hard, massive colony with a peculiar structure.

Figures

FIG. 74. — Diazona textura Monniot C., 1987; A, musculature; B, dorsal tubercle. Scale bars: A, 2 mm; B, 0.2 mm.

FIG. 124. — A, Diazona tenera Monniot F. & Monniot C., 1996; B, Diazona textura Monniot C., 1987; C, Rhopalaea circula n. sp.; D, Rhopalaea crassa (Herdman, 1880); E, Rhopalaea fusca (Herdman, 1880); F, Rhopalaea respiciens Monniot C., 1991.