The excretory system of Hutchinsoniella macracantha (Crustacea, Cephalocarida)

The primary excretory organ of adult Hutchinsoniella macracantha is the maxillary gland, which is located laterally in the posterior portion of the cephalon. It consists of an end sac and a tubule which is divided into proximal and distal sections. The end sac is composed of podocytes filled with endocytotic vesicles which grade in size upward to a large residual body. A large valve controls the opening connecting the end sac to the proximal tubule. The proximal tubule is distinguished by a dense lining of long microvilli. The distal tubule is lined with a thin cuticle. The excretory pore is a valvelike slit on the base of the posteromedial surface of the protopod of the second maxilla. In the nauplius, an antennal gland with similar morphology is located within the most proximal segment of the second antenna. In the adult, this gland appears to be nonfunctional.