Ultrastructure of the secondary body cavity in polychaetes of the family Phyllodocidae (Polychaeta, Annelida). 2. Polychaetes with developed bloody system

Two species, Paranaitis wahlbergi (Malmgr.) and Notophyllum, foliosum (M. Sars), of the family Phyllodocidae were studied. The results obtained were compared to the data on the morphology of coelom in other phyllodocides reported in the first communication. Generally, all the representatives of this family are similar in morphological features. The dorsal longitudinal muscles are arranged in two weakly separated ridges; ventral longitudinal muscles, in two distinct ones. Continuous circular muscular system is absent. Dissepiments are developed and consist of muscular cells. Coelomycetes are not found. Coelomic lining consists of simple myoepithelium, its cells form few cytoplasmic appendages. Both species have well-developed bloody systems. The level of developing the cytoplasmic appendages is related to the size of the bloody system, muscular cells, and of animals themselves. The degree of developing the cytoplasmic appendages, dissepiments, and the bloody system demonstrate adaptive features. Such morphological features, as the myoepithelial type of mesodermal tissues, muscle dissepiments, and the absence of coelomycetes and coelothelium may characterize the family as a taxonomic group. The developmental level, the type of circulatory system, and body size may determine ultrastructural features of the secondary body cavity.