The coral reefs along the Gulf of Aqaba consist of 14 species of crinoids with aggregations of different species in various depths. The most shallow group consists of several species of which the most common are Lamprometra klunzingeri and Heterometra savignii which occur in the shallow subtidal down to 2.0 to 3.0 metre depth. Other species of this group occur to a depth of 12 to 15 metres and from here another group of species occur which is headed by Decametra chadwicki and Oligometra serripinm, The deepest crinoids -were collected at a depth of 45 metres by SCUBA and the most common ones were found to be Colobometra arabica and Comaster brevicirrus.

Feeding on micro and nano-plankton, the shallow water population of crinoids showed a typical circadian rhythm/Whereas in groups occurring from 10 to 12 metres depth, this behaviour changes to a diurnal one gradually with the decrease in illumination.

Investigating the symbiotic animals living on the crinoids it was found that 27 taxons are involved in this interaction among them: Copepoda (6 species); Mollusca (2 species); Polychaeta (11 species) especially Myzostomida; Ophiurids (1 species); Crustacean decapod (6 species) and fish (Lepadichthys lineatus).

All these symbiotic animals were found to form typical food webs and groupings distributed according to the distribution of the host crinoid and depth. The occurrence of typical E, Indo-Pacific and Mediterranean Myzostomids on the same crinoid in the Gulf of Aqaba was found to be of special interest.