Proagnesia depressa

Proagnesia depressa (Millar, 1955)

(®gures 15A, 16B)

Agnesia depressa Millar, 1955: 223.

Proagnesia depressa: Monniot and Monniot, 1973: 418; 1974: 739.

Material examined. St. 4077, 3285± 3160 m, one specimen; st. 4104, 5110±5120 m, one specimen.

Description. The specimens are strongly contracted and are about 1 cm in diameter. The basal half is hemispherical with thin test. The upper surface is ¯attened, oval and covered by thicker and more rigid test. The apertures are on short siphons on the upper disk. The area around and between the siphons is covered by short thick crowded papillae, but the remainder of the upper disk is covered by long outgrowths which are sparse on the lower part of the body (which apparently was immersed in soft mud).

Thin crowded circular muscles are present around the apertures, and a conspicuous band of long thick parallel transverse muscles crosses the dorsal surface between the apertures and posterior to the atrial siphon. They closely resemble those ®gured by Monniot and Monniot (1974). We have not found any tentacles. The prepharyngeal band is composed of a single lamella and the dorsal V is absent. The neural ganglion and oval neural gland are halfway between the siphons. There are four long dorsal languets. The branchial sac has four high transverse vessels without papillae. Some stigmata spiral, but mostly they are irregular and it is not possible to count either the number per row, or the number of rows between two transverse vessels.

The gut loop makes a complete circle and the rectum is directed away from the atrial siphon. The stomach is relatively large, oval and smooth-walled. The anal border has long ®nger-like lobes. The gonad is in the gut loop, but gonoducts were not detected.

Remarks. The orientation of the rectum is probably an artefact. In previously described specimens the proximal part of the gut forms the usual loop and the rectum is, as usual, directed to the atrial aperture. The other features, especially the structure of the branchial sac and body muscles, are in agreement with existing accounts.

This is the ®rst record of the species from Antarctic waters. It was previously known from numerous records from the northern and central Atlantic, around South Africa and from central and northern parts of the Indian Ocean.