Oligotrema psammites Bourne, 1903

Kott, Patricia, 2009, Taxonomic revision of Ascidiacea (Tunicata) from the upper continental slope off north-western Australia, Journal of Natural History 43 (31 - 32), pp. 1947-1986 : 1983-1984

Oligotrema psammites Bourne, 1903

Oligotrema psammites Bourne 1903, p. 233 . Kott 1992, p. 650 and synonymy.

Distribution

Previously recorded ( Kott 1992): Atlantic Ocean ( Cape Basin ), tropical Indian Ocean , New Britain ; Indonesia, New Caledonia and the New South Wales coast. New records: CSIRO 05 / 07, western Australia ( Station 047-022 (part), Port Hedland, 19.14 S 117.77 E, 115 m, Sediment Grab, 4.6.07, one specimen, QM G328558 ; Station 068-028 Mermaid, 16.63 S, 119.15 E, 983 m, Beam trawl 17.6.07, two specimens, QM G328509 ) .

The species is known from the western Pacific, the Atlantic (including the Cape Basin) and the Indian Oceans, in waters from about 1000–4000 m deep. However, the type location of the newly recorded species from New Britain and the newly recorded specimen from off Port Hedland are from waters around 100 m depth, the shallowest recorded for this species. The previous Australian record of this species off the eastern Australian coast was at 1200 m. The shallow waters recorded in the western Pacific afford a route for gene flow between the Indonesian and western Pacific populations of this species and those in the Indian Ocean, the Cape Basin and the Atlantic Ocean.

Description

The newly recorded specimens are tough and contracted, to about 2 cm long, with the six large, characteristic and conspicuous pinnate arms surrounding the branchial aperture and the body coming to a point posteriorly in the small and inconspicuous atrial opening inclined postero-dorsally. Generally long hairs that enmesh sand are on ventrum and left side of the body but are absent from the other side where a thin layer of sand adheres to the test. The characteristic buccal cavity is produced forwards at the anterior end of the body, its margin lined by the six pinnate arms, the dorsal arms being longer. Strong circular muscles are in the body wall of the buccal cavity and a band of circular muscles is in the body wall behind it. Inside these circular muscles are longitudinal bands that extend posteriorly onto the anterior half of the body. Some short transverse muscles also extend across the dorsal surface along the remainder of the body. The inner walls of the pharynx have some concavities and pouches from which patches of ciliated stigmata open to the two anterior horns of the atrial cavity. The thick vertical oesophagus opens into a large curved stomach about three-quarters of the way down the body and a rectum curves around the stomach from its distal end and opens at the base of the small atrial siphon at the posterior end of the body. Bunches of branching testis follicles are at the proximal end of the long tubular ovary on each side and a large kidney with a conspicuous concretion is present. Gonads are partially embedded in a fleshy thickening of the body wall on each side. A long ligament separating the atrial cavity into right and left chambers attaches the mid-ventral line of the gut to the body wall.

Remarks

The specimens conform to those previously recorded. Difficulties and ambiguities in interpreting their morphology often arise through confusion in the terminologies used to describe them and from misinterpretation of the homologies of many of their organs. Most aspects of the morphology of species in this family appear to be closely related to structures in the family Molgulidae . They are distinguished from the latter family principally by compelling reductions in their filter feeding capacity.

The presence of long hairs on the ventral surface, the dorsal buccal arms being longer than the ventral ones and the postero-ventral orientation of the atrial opening all suggest that individuals lie on their ventral sides, rooted in sediments by the long hairs on that side of the body; with the atrial aperture directed away from, and the buccal chamber directed toward, the substrate. This orientation suggests the possibility that the food organisms of these specimens are interstitial rather than planktonic or pelagic.