Class: Holothuroidea de Blainville , 1834 Orders Subclass Apodacea Apodida Molpadiida Subclass Aspidochirotacea Aspidochirotida Elasipodida Subclass Dendrochirotacea Dactylochirotida Dendrochirotida Sea cucumbers are echinoderms from the class Holothuroidea . They are marine animals with a leathery skin and an elongated body containing a single, branched gonad . Sea cucumbers are found on