Some aspects of the fine structure of the sense organs and neuroendocrine system of archaeogastropods

Abstract

The investigations reported in this thesis have been carried out primarily on British representatives of the Archaeogastropoda. The work falls into two parts the first relates to the fine structure of epithelial sensory cells and the second to the fine structure and function of the juxtaganglionar organ, a putative endocrine gland.

Observations on the sensory cells are primarily concerned with those found in the cephalic and epipodial tentacles, and the epipodial sense organs. The general organisation and innervation of these structures is described together with the ultrastructure of their sensory cells. The species examined most extensively were Gibbula umbilicalis (da Costa) and Emarginula reticulata Sowerby. Much similarity was observed between these species, particularly with regard to the epipodial sense organs. Similar structures were also found on the mantle edge bordering the shell slit of E. reticulata. Members of the Patellacea were examined briefly for comparison.

Fine structural observations on the juxtaganglionar organ were carried out on G. umbilicalis. The organ was found to possess many features characteristic of an endocrine gland and to show similarity to the dorsal bodies of pulmonates. Animals were collected at monthly intervals throughout one year in order to investigate the possibility of seasonal variation in the activity of the organ. Such variation was observed in females and was shown to correlate with the reproductive cycle. Males were not examined in this respect. The juxtaganglionar organ of an opisthobranch, Aplysia punctata Cuvier, was examined for comparison. It was found to exhibit further similarity to the pulmonate dorsal bodies.