Tubular and glandular organs in the Cladocera, Chydoridae

Abstract

Chydorid cladocerans of three closely related genera–Chydorus, Peracantha and Pleuroxus– possess a long, blindly‐ending tubular organ which lies freely in the haemocoele but follows a precise course between the organs of the body, and which ultimately unites with the alimentary canal in the rectal region. No such organ is present in Pseudochydorus globosus which, until recently, was assigned to the genus Chydorus. This species, like representatives of at least seven, and probably more, chydorid genera, has a much shorter glandular organ which, although markedly different in form, may, however, be homologous with the tubular organ. In Alona affinis what is perhaps a precursor (or regressive rudiment) of a glandular organ is present. All these are described and the only partially‐elucidated situation in Alonella exigua is mentioned. In Eurycercus lamellatus and Leydigia leydigii no trace of either a tubular or a glandular organ is present. The function of these organs is unknown. Mention is made of their possible phyletic and taxonomic significance.