SYMBIOTIC POLYCHAETES PROCERAEA SP. (POLYCHAETA, SYLLIDAE) AND MODIFICATION OF HYDROTHECAE IN HYDROID ABIETINARIA-TURGIDA (HYDROZOA, SERTULLARIIDAE)

Numerous small polychaete Proceraea sp. were found inside the hydrothe cae and mucous tubes attached to stems of the colonial hydroid Abietin aria turgida (Clark, 1976) at the coast of Mednyi Island (Commander Is lands). The species remains unindentified due to the absence of mature adult specimens. Morphology of Proceraea sp. larvae and juveniles are described. In each hydrotheca there is only one polychaete at differe nt stages of development, from achaetous larvae to juveniles with 10-1 1 segments. The juveniles of 1.0-1.1 mm long leave the hydrothecae and form mucous cylindrical tubes attached to the stem of branches of hyd roid. The presence of larvae inside the hydrothecae stimulates modifyi ng its form. The infested polyps produce the cylindrical elongation at tached to distal edges of the thecae. The preavalence (ratio between t he number of the thecae infested with polychaete and the total number of thecae in each colony) varies from 3.8 to 33.0%. Disappearance of p olyps in the infested hydrothecae as well as the presence of pigmented granules, which are characteristic of hydroid tissues inside the poly chaete intestine, are an evidence of feeding polychates upon hydroids. The polychaete-hydroid interrelations is considered as parasitism. Pr oceraea sp. females are supposed to lay their eggs into hydrothecae of alive A. turgida. A model of the Proceraea sp. life cycle consisting of parasitic (larvae and juveniles) and free-living phases are discuss ed.