Holothuroidea | EchinoID

Holothuroidea or sea cucumbers

Sea cucumbers are among the most common invertebrates in the shallow waters of Oman. Holothuroids have lost most of the intra-dermal skeletal structures characteristic of the echinoderms. Their skeleton is reduced to minute spicules imbedded in the tegument of animal and a ring of small plates surrounding the oesophagus. Both these small skeletal structures are important in species taxonomy but are invisible on the live organism. The absence of skeletal plates allows the sea cucumbers to change shape dramatically and move into crevices apparently much too small to accommodate them. In addition, they have some control over the collagen fibers that structure their body wall and can thus change from a "solid" to a semi-liquid collagen form. This allows them to lock their body in crevices or underneath boulders and rocks.
Sea cucumber either feed on the fine particles of organic matter (decomposing matter, bacteria, benthic phytoplankton,…) found at the surface or between the particles of sand of the bottom. They collect this rich sediment with a ring of tentacles surrounding the mouth. Most species described here belong to this category (Aspidochirotes). Another group includes species feeding on the particles in suspension in the water column (the Dendrochirotes). In this latter group, the oral tentacles are much larger and when extended shaped like tree branches. A third group, the Apoda, have only retained the oral tentacle, all all podia have disappeared. The only illustrated species here is Euapta geoffroyi: one of the largest of all holothuroidea: often more than 1m long.
There are some 20 known species of Holothuroidea in the shallow waters of Oman.
The structure of the identification key is not based on the taxonomy of these organisms but on their appearance alive in the ocean.