Trididemnum inermum, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 263-264

publication ID	https://doi.org/ 10.5281/zenodo.5391440
persistent identifier	https://treatment.plazi.org/id/F57D87A3-FFE1-3104-EBBA-FCF6FDE81380
treatment provided by	Marcus
scientific name	Trididemnum inermum
status	sp. nov.

Treatment

Trididemnum inermum View in CoL n. sp.

( Figs 49 View FIG ; 119D)

TYPE MATERIAL. — Papua New Guinea. Coral Sea, eastern Fields, 10°09.35’S, 145°33.92’E, 31 m, 15. VI.1998 ( MNHN A2 TRI 150).

ETYMOLOGY. — From the Latin inermus: without arms.

DESCRIPTION

The largest colony is 6 cm in extent and 2 mm thick. It is semi-transparent, colourless (Fig. 119D) and without any spicules. It is lobed, mammillated, with wide common cloacal openings. The colony’s consistency is fleshy and rather firm. The tunic is resistant, making the small zooids difficult to extract. There are large cloacal channels, some of them occupied by shrimp.

A long waist elongates the zooid between the thorax and the abdomen ( Fig. 49A View FIG ). The oral aperture is small with six lobes. The cloacal siphon makes a short tube, directed backwards, encircled by a sphincter. The 24 oral tentacles are short and in three orders of size. There is a

A wide unperforated area anteriorly ( Fig. 49A View FIG ). The branchial sac is large with up to 15 stigmata in the first half row. The second row is slightly shorter but the last row is long and protrudes slightly below the level of the cloacal siphon.

The retractor muscle is very short ( Fig. 49A View FIG ), thread-like, arising from the upper part of the long oesophageal peduncle. The gut forms an elongated loop. The single testis follicle occupies its centre, covered with five to eight turns of the sperm duct ( Fig. 49B View FIG ). The first turn is set apart from the adjacent coils. The ovary, poorly developed in this specimen, is located against the testis.

No larvae were found.

In some but not all zooids, very small spots can be seen on each side of the thorax near the cloacal siphon. They may be an indication of lateral thoracic organs, but no trace of spicules was found in the colonies.

REMARKS

This species differs from other Trididemnum in its total absence of spicules and its massive and lobed colonies. It lacks the pigment which is present in the black, almost spicule-less, species Trididemnum discrepans ( Sluiter, 1909) .