Difficult Sea Cucumber

H. difficilis is a member of the phylum Echinodermata meaning they share a general body plan with other members of the phylum. These traits include pentamerous radial symmetry, an endoskeleton, an oral side opposite of an aboral side, a water vascular system, and tube feet. The oral side contains the mouth for feeding and the aboral side contains an anus used to rid of waste and for respiration. Tube feet is used for locomotion. H. difficilis also contains several mechanisms for defense. Structurally, their dermis is noxious and they also contain very thin Cuvierian tubules that can be ejected. It has been hypothesized these defense mechanisms, that animals such as Holothurians have, are due to evolution against predation. This species contains one gonad and can perform sexual reproduction.

The species has been found in many seas and oceans across the globe such as the Red Sea, and near Central America. However, its general distribution is in the Indian and Pacific Oceans. Typically, this species is benthic and lives inshore. When observed in La Reunion Island fringing reefs, the species resided in outer reef flats and under large boulders.

The main predator of H. difficilis are sea stars. However, they are also preyed upon by fish. Sea stars are able to wholly ingest sea cucumbers whereas fish typically can only eat certain because of H. difficilis' dermal toxicity.