Polychaetes living on Echinoderms (Summary): In the Red Sea the two polychaetes Gyptis ophiocomae n. sp. and Podarke pugettensis spinapandens n. ssp. were found associated with Echinoderms. Podarke pugettensis spinapandens lives on the sand dollar Clypeaster humilis on whose shorter spines it moves while the longer spines go aside, pedicellaria do not attack the worm. Gyptis ophiocomae lives on the brittle star Ophiocoma scolopendrina. There is generally a striking colour correspondence between the serpent star and its polychaetous associates. Both species are described and compared to other species of the same genera living in the Indo-Westpacific region. The way of moving is explained and the segmental musculature is described.