DEVELOPMENT OF THE HYALINE LAYER AROUND THE PLANKTONIC EMBRYOS AND LARVAE OF THE ASTEROID PATIRIELLA CALCAR AND THE PRESENCE OF ASSOCIATED BACTERIA

The hyaline layer (HL) around the embryos and larvae of Patiriella cal car is examined by transmission electron microscopy. P. calcar hatches at the gastrula stage and develops through a lecithotrophic planktoni c brachiolaria. The hyaline layer of unhatched P. calcar is poorly dev eloped and is comprised of wispy fibrils scattered among the epithelia l microvilli. Fibrils are also occasionally seen associated with the i nner surface of the fertilization envelope. By the hatched gastrula st age, the hyaline layer is organized into three strata: the intervillou s layer, the supporting layer and the coarse outer meshwork layer. Sev en-day-old brachiolaria also have a hyaline layer comprised of three s trata. In these larvae the supporting layer elevates away from the epi thelial surface due to the tuft-like organization of the underlying mi crovilli. This results in the formation of local outpockets giving the surface of the HL a lobed appearance. Bacteria are occassionally seen in the intervillous layer, particularly in association with the outpo ckets. These bacteria are phagocytosed by the epithelial cells and, in larvae that have bacteria, may play an augmentive role in larval nutr ition. The structure of the hyaline layer of P. calcar is compared wit h that of the hyaline layer of other Patiriella species to determine i f it is more similar to the external coats around its planktonic (P. r egularis) or benthic (P. exigua) developing congeners. The comparison shows that the hyaline layer of P. calcar is virtually identical to th at of P. regularis, a similarity that may reflect the pelagic life his tories of these species.