Diazona fungia, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 291-292

Diazona fungia n. sp.

( Figs 72 ; 123E )

TYPE MATERIAL. — Fiji. Somosomo Straits, wall, 16°47.88’S, 179°54.09’E, 53 m, 3.XI.1996 ( MNHN P1 DIA 46).

ETYMOLOGY. — From the Latin fungus: mushroom.

DESCRIPTION

The colonies are massive, pedunculate, and look like mushrooms (hence the species name). The “heads” measure 3 to 4 cm in diameter, the peduncle 2 to 3 cm in diameter and 4 to 5 cm in length. In life the colonies are white ( Fig. 123E ) and the pigment is diffuse. There are no circles around the siphonal apertures, which protrude very slightly in a transparent tunic. When formalin-fixed the colour turns yellow-grey. There are some encrusting bryozoans at the base of the colony. The zooids are located in the “head” of the colony, the base of the abdomens being sometimes slightly included in the peduncle. The tunic is harder on the peduncle and contains only the vascular processes. The tunic is soft around the thoraces, a little more resistant around the abdomens. A ring of fibrous and more resistant tunic encircles the top-part of the oesophago-rectal area. The thorax and abdomen are equal in length. A long vascular process extends from the abdomen. The oral siphon is terminal with six flat lobes. The cloacal siphon is longer with six sharp lobes ( Fig. 72A ). The muscles ( Fig. 72A ) are gathered in bundles starting from the dorsal side of the body. These branch along the endostyle and constitute the muscles extending along the abdomen. The siphonal musculature becomes oblique in the anterior third of the thorax. On the abdomen, the muscle fibres are spaced well apart before converging into two bundles along the stomach and ending without protrusions at the base of the intestine ( Fig. 72B ).

There are 12 oral tentacles in two orders and some smaller ones intercalated. They are planted on a crest that makes large undulations to connect the base of the largest tentacles. The prepharyngeal band has only one blade and is deeply curved dorsally. The dorsal tubercle is round, close to a diffuse neural gland. The dorsal languets are long and generally correspond to each transverse vessel, but exceptionally there is only one languet per two vessels.

The branchial sac is cylindrical, slightly narrowed in its posterior part. There are 50 to 55 rows of stigmata and about 35 longitudinal vessels on each side, most of them complete. The branchial tissue is flat; the meshes are elongated with only two stigmata apiece.

The gut is embedded in an opaque tissue layer of irregular thickness in different zooids ( Fig. 72C, D ), obscuring the different parts of the gut. In section, the stomach has deep grooves ( Fig. 72C ). The rectum is long and opens by a bilobed anus at the base of the cloacal siphon. No zooids in these specimens have mature gonads. The sperm duct runs along the rectum and opens at a short distance behind the anus.

REMARKS

This species differs from all other Diazona in the shape of the colony. The musculature has principally transverse fibres as does Diazona textura , but in the latter they ramify in the ventral part of the body. D. fungia n. sp. differs from D. pedunculata n. sp. in the size of the zooids, the length of the abdomen, and the thoracic musculature.

Figures

FIG. 72. — Diazona fungia n. sp.; A, musculature of the thorax; B, abdomen; C, section at the stomach level; D, section at the heart level. Scale bars: A, B, 2 mm; C, D, 1 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.