Microscopic anatomy of the integument and digestive system during the molt cycle in Ligia italica (Oniscidea)

The molt cycle of Ligia italica was divided into four stages with altogether eight sub-stages. The average duration of the molt cycle was determined in laboratory animals. Males and non-breeding females molt every 15 days, breeding females molt every 34 days. Molt-related changes in the infrastructure of the anterior sternal integument and digestive system were investigated with scanning and transmission electron microscopy. Calcium storage and translocation in the integument and the midgut glands during the molt cycle were examined with cytochemical methods. The total calcium concentrations in the midgut glands and haemolymph were determined. Calcium is resorbed from the old cuticle prior to ecdysis and stored as calcium granules in the ecdysal space. In the intramolt animal the resorbed calcium is transported, via the haemolymph, to me posterior part of the integument for the mineralization of the new cuticle. The epithelial cells of the digestive tract with high glycogen content and variously shaped apical parts direct the differentiation of the cuticular structures in the foregut and the hindgut during the premolt stage. The ultrastructure of the midgut and midgut glands also changed during the molt cycle. Changes in the lipid content and distribution were observed in the large cells of the midgut glands throughout the molt cycle. Numerous calcium granules in the small cells of the hepatopancreas of premolt animals may be the source of calcium employed for the mineralization of the cuticle of the digestive tract.