FURTHER OBSERVATIONS ON THE STRUCTURE AND FUNCTION OF THE OPERCULUM IN SPIRORBIS MOERCHI (SERPULIDAE: SPIRORBINAE)

¹ Department of Zoology, University of Massachusetts at Amherst, Amherst, Massachusetts 01003

1. The ultrastructure of the opercular epithelium in Spirorbis moerchi, with special emphasis on the structure of the pore epithelium in brooding and nonbrooding individuals, has been described.

2. In brooding worms, the epithelium bordering the closed opercular pore consists of tall columnar cells. Each cell is characterized by the presence of long microvilli, apical intercellular spaces, an apical ring of membrane associated microfilaments, and bundles of microfilaments arranged parallel to the longitudinal axis.

3. After larval release, the opercular pore remains open, although not maximally, and the cells bordering the pore, including their microvilli and apical intercellular spaces, are now reduced in height. The cells contain an apical filamentous network and a subapical ring of membrane associated microfilaments, but lack the longitudinal bundles observed in the brooding condition.

4. The role of microfilaments, together with other aspects of the ultrastructure of the opercular epithelium, are discussed.