Distribution and swimming ability of the deep-sea holothuroid Penilpidia ludwigi (Holothuroidea: Elasipodida: Elpidiidae)

Abstract

The deep-sea elpidiid holothuroid, Penilpidia ludwigi, was recorded using a Remotely Operated Vehicle in the Western, Central, and Eastern Mediterranean Sea. This species, endemic to the basin, was previously captured above the seabed in sediment traps and based on these records its swimming ability was assumed. The present study reports the first in situ observations of swimming P. ludwigi and provides an update on the geographic and bathymetric distribution of this species. A large aggregation of thousands of specimens was observed in the Levantine Sea with a maximum local density 300 ind. m−2. The ROV surveys allowed observation of the behavior of the species and description of its mode of swimming. Active swimming using strokes of the tentacle crown is combined with drifting benefiting of the current, the former used for fast escape the latter mainly for energy-saving displacement. Swimming behavior allows P. ludwigi to exploit various deep-sea habitats including seamounts, canyons, and ridges inaccessible to non-swimming deposit feeders.