Alterations in the mantle epithelium during transition from hatching gland to adhesive organ of Idiosepius pygmaeus (Mollusca, Cephalopoda).

Epithelial gland systems play an important role in marine molluscs in fabricating lubricants, repellents, fragrances, adhesives or enzymes. In cephalopods the typically single layered epithelium provides a highly dynamic variability and affords a rapid rebuilding of gland cells. While the digestive hatching gland (also named Hoyle organ) is obligatory for most cephalopods, only four genera (Nautilus, Sepia, Euprymna and Idiosepius) produce adhesive secretions by means of glandular cells in an adhesive area on the mantle or tentacles. In Idiosepius this adhesive organ is restricted to the posterior part of the fin region on the dorsal mantle side and well developed in the adult stage. Two gland cell types could be distinguished, which produce different contents of the adhesive. During the embryonic development the same body area is occupied by the temporary hatching gland. The question arises, in which way the hatching gland degrades and is replaced by the adhesive gland. Ultrastructural analyses as well as computer tomography scans were performed to monitor the successive post hatching transformation in the mantle epithelium from hatching gland degradation to the formation of the adhesive organ. According to our investigations the hatching gland cells degrade within about 1 day after hatching by a type of programmed cell death and leave behind a temporary cellular gap in this area. First glandular cells of the adhesive gland arise 7 days after hatching and proceed evenly over the posterior mantle epithelium. In contrast, the accompanying reduction of a part of the dorsal mantle musculature is already established before hatching. The results demonstrate a distinct independence between the two gland systems and illustrate the early development of the adhesive organ as well as the corresponding modifications within the mantle.