Diazona pedunculata, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 292-293

Diazona pedunculata n. sp.

( Figs 73 ; 123F )

TYPE MATERIAL. — Papua New Guinea. South coast, Coutance Island on barrier reef, overhang, 10°13.80’S, 148°06.87’E, 33 m, 13. VI.1998 ( MNHN P1 DIA 48). ETYMOLOGY. — From the Latin pedunculus: peduncle. OTHER MATERIAL EXAMINED. — Papua New Guinea. South coast, 100 miles SE of Port Moresby, Cape Rodney Pass, 10°15.66’S, 148°22.27’E, 25 m, 11. VI.1998 (Sample: CRRF).

DESCRIPTION

The pedunculate colonies are as long as 10 cm. The peduncle, about 1 cm in diameter, is rather hard at the surface and carries some epibionts. It is divided into two or three branches each ending in a very soft and clear inflated head. The siphons, circled with a white pigment ( Fig. 123F ), do not show any special pattern at the colony surface. There is no sand at all in the tunic.

The zooids are extremely long ( Fig. 73C, D ). The thorax measures 3 mm in length in the less contracted zooids, while the abdomen reaches 25 mm. The oral siphon has six flat lobes; it is well apart from the cloacal aperture. The thoracic musculature ( Fig. 73A ) is regularly arranged with straight, parallel longitudinal bundles issuing from the oral siphon, then curving at their posterior ends to reach the medio-dorsal line. The shortest bundles are those arising nearest to the cloacal siphon, and the more ventral muscles are progressively longer. There is no muscle on the ventral line. The musculature is thin on the abdomen, ending grouped in two weak bundles at the abdominal extremity ( Fig. 73B ). They do not penetrate into the very long and thin vascular process that extends into the peduncle of the colony.

The branchial sac has about 22 rows of stigmata. The longitudinal vessels are generally complete ( Fig. 73E ) and bear short papillae. There are one to two elongated stigmata in a mesh. The stigmata rows are interrupted dorsally. The dorsal lamina is made of long, sharp languets. It is not displaced on the left side of the body.

The abdomen is particularly long and very thin ( Fig. 73C, D ), except at the posterior extremity, where it is inflated to contain the stomach and the gonads ( Fig. 73B ). The wall of the barrel-shaped stomach has uninterrupted folds. The intestine does not show individualised compartments.

The gonads comprise a few testicular follicles inside the gut loop behind the stomach and an ovary with numerous oocytes placed against the testis ( Fig. 73B ). Many gonadal lobules or “pseudooocytes” are accumulated at the base of the ascending limb of the gut and make a line along the rectum. The sperm duct follows the rectum and extends beyond the anus to open at the base of the cloacal siphon.

REMARKS

D. pedunculata n. sp. differs from all other described Diazona except D. fungia n. sp. in its pedunculate colony. It differs from D. fungia n. sp. in the colony shape, smaller zooids, a much longer abdomen, and a different thoracic musculature.

Figures

FIG. 73. — Diazona pedunculata n. sp.; A, musculature of the thorax; B, abdomen; C, D, both part of a zooid; E, part of the branchial sac. Scale bars: A, B, 1 mm; C, D, 2 mm; E, 0.3 mm.

FIG. 123. — A, Atriolum robustum Kott, 1983; B, Leptoclinides madara Tokioka, 1953; C, Leptoclinides subviridis (Sluiter, 1909); D, Diazona formosa Monniot F. & Monniot C., 1996; E, Diazona fungia n. sp.; F, Diazona pedunculata n. sp.