ABSTRACT
The geographical distribution of elpidiid genera demonstrates that all primitive elpidiids are distributed either in the tropical region (Psychrelpidia, Penilpidia), or in the Antarcic (Rhipidothuria, Protelpidia), implying thus the key role of these two regions in the evolution of the deep-sea holothurian fauna. The modern distribution of very closely related Psychrelpidia and Rhipidothuria , the first being known from the Indo-Malayan area, and the second from the Antarctic (particularly, from the Antarctic Peninsula area), forms a bridge between these two regions. We have every reason to believe that the elasipodid fauna was widely distributed in the ancient Tethys Sea basin, and was split into at least three parts, following the break up of the Tethys Sea into the Indo-Malayan, the Mediterranean and the West Indian sections, the latter remaining in the Panama Gulf area after this region has been split in two by the Central American Isthmus. The subsequent invasion of the Antarctic occurred most probably along the South American continental slope in the bathyal zone, and a new stage in the history of deep-sea holothurians, the penetration of abyssal waters and their resultant world wide distribution, started in the Antarctic.
