CONTRAMYZOSTOIMA BIALATUM (ANNELIDA, MYZOSTOMIDA), A NEW GENUS AND SPECIES OF PARASITIC MYZOSTOME INFESTING COMATULID CRINOIDS

The external and internal morphology of a new genus and species of par asitic myzostome is described from the territorial waters of Singapore . Contramyzostoma bialatum, new genus and new species, infests the arm s of the crinoid Comaster gracilis where it occurs in burrow-like inte gumental cavities. Contramyzostoma bialatum is characterized by a dors al body field bearing all the external appendages (viz., five pairs of parapodia, four pairs of lateral organs, two pairs of cirri, and an a no-genital cone) and by two large wing-like body extensions. The diges tive system comprises a pharynx included in an introvert, several sali vary gland cells, a stomach from which originate two loop-shaped diges tive tubules, and an intestine. All individuals examined were females possessing two ovaries and a branched oviduct. The infestation by C. b ialatum produces significant modifications of the host epidermis and d ermis.