ИСТИНА

Hypomyzostoma jasoni is an ectocommensal myzostome associated with feather star Stephanometra indica (Smith 1876). Worms steal food from ambulacral grooves and occur located on the host’s arms and pinnules. One S. indica specimen may be inhabited by a group of up to 40 hypomysostomes of different ages. Coloration of H. jasoni matches the color pattern of the host. In small groups, up to 8–10 specimens of adult worms are usually white with 10–11 transverse dark-brown strips, and sit on the host with the body oriented along the arm of crinoid, whereas young worms are brown with single longitudinal mid-dorsal white strip, and occur on pinnules. Worms of middle size, having some intermediate coloration with pale transverse strips and single bright longitudinal one, occur mostly on arms or on large pinnules. In large groups with more then 10–15 specimens, H. jasoni have the same types of coloration, but without exact dependence on body size. Both small and large worms with one single strip are present. Perhaps the reason for this is that S. indica is a small crinoid with a small number of arms and thin pinnules, therefore, H. jasoni have to compete for feeding places with each other. If for some reason a worm cannot take a favorable food place on the host's arm, it may be forced to remain on the pinnule, and “young” coloring with a single longitudinal strip remains in the adult. The Russian Fund for Basic Researches supports this study (19- 04-00501, 18-05-60158).