Structure and function of the maxillary nephridium of Lithobius forficatus (Chilopoda, Pleurostigmophora).

Notostigmophora and Lithobiomorpha are the only Chilopoda that have maxillary nephridia. The ultrastructure of the maxillary nephridium in Scutigera coleoptrata was described, but only light microscopic descriptions of this excretory organ of Lithobius forficatus are available. Therefore, we studied the ultrastructural organization of the maxillary nephridium of L. forficatus. In this species, the paired maxillary nephridium lies lateral to the pleuroventral longitudinal musculature in the region of the 1st and 2nd maxilla. The nephridium is partitioned in three compartments: a wide sacculus and a nephridial canal formed by a sac-like labyrinth and a bean-like utriculus. The sacculus opens with two different openings to the labyrinth. The labyrinth and the utriculus are connected by a short canal. Each nephridium opens to the exterior by two conducting canals. The lumen of the sacculus is lined by podocytes. The nephridial canal is formed by a high-prismatic transport epithelium with a wide microvillar border and a high basal labyrinth. Only the epithelium of the utriculus is covered by a cuticle. Here, we compare the maxillary nephridia of L. forficatus (Pleurostigmophora) with that of Scutigera coleoptrata (Notostigmophora) in regard to their functional morphology, the mode of life of these species, and their excretory products.