Fine structural and immunocytochemical studies on the eyeless aesthetes of Leptochiton algesirensis, with comparison to Leptochiton cancellatus (Mollusca, Polyplacophora).

The aesthetes of Leptochiton algesirensis (Capellini, 1859) and Leptochiton cancellatus (Sowerby, 1840) consist of six to eight microaesthetes surrounding one macroaesthete. The monocellular microaesthetes include many microtubules, neurosecretory vesicles, and unperforated, subsidiary caps. Basally they are in contact with tiny nerve processes via probably electrical synapses. Each macroaesthete consists of a perforated apical cap and various cell types: flattened peripheral cells, various types of mucous cells, and three or four monociliary sensory cells. Although lacking photoreceptors, the aesthetes of Leptochiton algesirensis combine storage-secretory and sensory functions. The latter function is confirmed by positive immunoreactions against (neuro-)tubulin and synaptophysine. The high degree of structural and functional similarity between polyplacophoran aesthetes and the analogous caeca of brachiopods is demonstrated.