The ultrastructure of the hepatic cells in millipedes (Myriapoda, Diplopoda)

The hepatic cells are characteristic cells that occur in millipede body where they form a continuous layer which surrounds the midgut epithelium. The following species, which represent five millipede orders were selected: Julus scandinavius (Julida), Polyxenus lagurus (Polyxenida), Polydesmus angustus (Polydesmida, Polydesmidae), Strongylosoma stigmatosum (Polydesmida, Paradoxosomatidae), Epibolus pulchripes (Spirobolida, Pachybolidae), and two species of the order Spirostreptida, Archispirostreptus gigas and Telodeinopus aoutii. The hepatic cells are absent in P. lagurus in which the midgut epithelium is surrounded by the visceral muscles. In the other species they were arranged around the midgut as coherent hepatic cells of mesenchymal character. Each hepatic cell possessed its own basal lamina and formed the cellular processes which protrude into the basal lamina of the midgut to make contact with midgut digestive cells. Accumulation of reserve material in different millipede taxa has been described with the special emphasis on the process of autophagy in the cytoplasm of the hepatic cells. The lack of hepatic cells may represent an ancestral condition within millipedes.