Studies of the reproductive biology of deep-sea megabenthos. I. The echinoderm species Laetmogone violacea and Benthogone rosea (Elasipoda: holothuroidea)

Specimens of the holothurians Laetmogone violacea and Benthogone rosea were examined from a number of stations (972 to 2120 m depth) in the Porcupine Seabight and Rockall Trough, N.E. Atlantic. Both species are gonochoric and show an equal division of the sexes. The ovary of Laetmogone violacea is a compact nodose structure containing eggs up to 400 μm diameter. The testis is highly digitate, with the wall of each tubule containing numerous infoldings lined with spermatogonia and spermatocytes; spermatozoa reach a maximum size of 2 μm (head diameter). The ovary of Benthogone rosea consists of thin-walled nodose tubules through which the large egg of 750 μm diameter can be clearly seen. The testis of B.rosea is a small digitate structure, the walls of which lack the infoldings found in L. violacea; spermatozoa have a head diameter of 5 to 7 μm. In neither species is there any evidence for reproductive seasonality. (author)