Aplidium benhami Brewin, 1946

(Figures 1, 2)

Aplidium benhami Brewin, 1946: 95 Fig. 4, pl.2 fig. 1–4; 1958: 439; 1960: 119, New Zealand

Stations. TR 6 (MNHN A1 APL.B 549). TA 22 (MNHN A1 APL.B 548). TA 56 (MNHN A1 APL.B 547).

All colonies have the same shape in thick crusts 1 to 2cm thick with a naked undulated surface. When alive (Fig. 1 A,B) the photos clearly show the circular systems of white zooids in a colourless translucent tunic which turns dark when in formalin (Fig. 1 C). The common cloacal opening of each system protrudes in a membranous central chimney. There is no incrustation in the tunic, some sand is present when there has been contact with the substrate. The zooid systems are well spaced and look like those of botryllids. The zooids are easily extracted from the tunic and embedded in mucous. In formalin, the body wall contains pigment cells (either white or black according to the colonies). The 6 lobes of the oral aperture are not pigmented but the muscle ring below them is white or yellow. The rim of the atrial aperture is also white or yellow in formalin; there is a short triangular colourless languet with sometimes 2 lateral teeth. The branchial sac has 10 to 12 rows of 10 stigmata on each side (Fig. 2 A). The transverse vessels are pigmented. The stomach has 20 to 24 longitudinal folds and there is an annular poststomach. The post-abdomen is long and reaches 1cm.The ovary lies far from the abdomen and at least in the middle of the post-abdomen (Fig. 2 C). It is followed by a double row of testis vesicles. A single larva (Fig. 2 B) occupies the whole space of the atrial cavity. The tail is wound in one and a half turns around the 800µm trunk. The 3 adhesive papillae alternate with 4 long vesicles; in addition, 4 round vesicles are on each side and groups of small ampullae are placed ventrally and dorsally on each side of the trunk.

The precise description given by Brewin (1946) leaves no doubt about the species identification.

A benhami was only recorded from the southern New Zealand.