(®gure 20)
Dimeatus attenuatus Sanamyan, 2000.
Material examined. St. 4090, 6145±5680 m, about 150 specimens.
Remarks. The genus Dimeatus comprises two closely related species, the type D. mirus Monniot and Monniot, 1982 and D. attenuatus. The genus is probably most unusual among Ascidiacea and was originally assigned to the Cionidae. It has two large atrial openings and very peculiar gonads, which do not resemble the gonads of Ciona in any way. In D. mirus, gonads were poorly developed and their structure was not determined, although it was reported that they were in the gut loop (Monniot and Monniot, 1982). The specimens from the present collection all have welldeveloped gonads and the male and female ducts always penetrate the test and open directly to the exterior by multiple openings. In all other ascidians the gonoducts open into the atrial cavity.
Dimeatus is the sole genus of the family Dimeatidae Sanamyan, 2000. For further discussion and full description see Sanamyan (2000).
Dimeatus attenuatus was found only at one station, but as many specimens. The same is true for D. mirus. Apparently, they form rare compact settlements of many individuals.