On base of data from literature and anatomic analysis of the material possessed the author gives a description of the parasite Sphyrion lumpi (Krøyer) and of the host's reaction (Sebastes marinus L.) upon its presence. As shown on photo 4 the connective tissue sac formed by the host around the cephalothoracal part of the parasite looks like a matrix in which all morphological details of this part of the parasite body are modelled out. The walls of the sac have a fibrous structure and are closely concreted with connective forme membrans separating myomers (myocommata).