THE FINE STRUCTURE OF ZOOIDAL TUBES IN SABELLIDITIDA AND POGONOPHORA WITH REFERENCE TO THEIR AFFINITY

Abstract.- Organic tUbes of Sabelliditidae are a characteristic element of Lower Cambrian faunas. They were commonly compared with tubes of sedentary polychae-tes, until Sokolov ·(1965) suggested their close affinity with Recent pogonophores. The aim of the present paper is to verify the latter hypothesis through a better understanding of ultrastructural features of zooidal tubes in both groups considered. The ultrastructure of the tube in Sabelliditida recognized for the first time by Urbanek, 1976 (in press), reveals that the wall of the tube is composed of two almost homogenous layers- the outer one and the inner one, and of the middle distinctly laminar layer. Characteristic wrinkles on the outer surface of the tube are made solely of the outer layer which is almost homogenous or with faint traces of some lammiation. The tubes in all Pogonophora under study display an entirely laminar structure. Wrinkles observed on certain areas of the tube are due to foldings involving nu-merous layers of the tube wall. Earlier biochemical and ultrastructural data and results of our ultrahistochemical observations are indicative of the presence of chi