Ultrastructure and morphology of the elytrum of scaleworm Lepidonotus squamatus Linnaeus, 1767 (Polychaeta, Polynoidae)

Abstract

The prey defensive strategy of the scale-worms can be divided to 3 different strategies. First one is symbiosis, the second defense strategy is to autotomize scales, and the third defense strategy is to curl into the ring and to protect the body by thick scales with big and sharp tubercles. The aim of this paper is to present the morphological, ultrastructural, and immunohistochemical studies of the scale of Lepidonotus squamatus. Elytrum of L. squamatus is composed from a dorsal and ventral single-layered epithelium covered with cuticle. The middle compartment is crossed by the ramifications of a nervous plexus. Dorsal cuticle is thicker than ventral and bears numerical macrotubercles of irregular shape. Elytrum is innervated by a single ganglion, situated in the base of elytrophor. Both FMRFamide- and 5HT-positive elements are presented in the ganglion. Laterally thick nerve bundles emerge from the elytrum ganglion to the thickness of elytrum. In the proximal part some fine neural processes protrude between the lower lateral margins of the epithelial cells and go inside papillae. In the distal parts nerves are lying in the middle between dorsal and ventral epithelium. We suppose that nerve fibers of neuroglia form a “chanell” inside the tissue, which is filling elytrum.