A reclassification of the anomopod families Macrothricidae and Chydoridae,with the creation of a new suborder, the Radopoda (Crustacea : Branchiopoda)

An investigation, using optical microscopy and SEM, of the trunk limbs of t he Anomopoda has revealed a large number of characters, previously underuse d or unused in taxonomy and comparative morphology. All these characters, w hich are nicely paralleled by some more conventional traits (head shield an d pores, postabdomen, antennae...), show one clear tendency across all grou ps studied: a state of complexity at one extreme, and a state of often inci sive simplification at the ether extreme, with a number of transitional sta ges in between. The complex character state, which itself is a simplificati on of the leg structure of the Ctenopoda and other, 'large' Branchiopoda, i s here considered to represent a primitive condition. The simplified state is considered advanced. Based on this assumption, we list a number of unify ing characters (mainly structural aspects of P1 and P2, but also the gnatho base of P3 and P4) for all macrothricid and chydorid-like anomopods, which we unite in the new suborder Radopoda. Non-radopod Anomopoda are not reclas sified. We then derive a cascade of (mainly trunk-limb based) characters to work out a hypothesis on the evolution of the Radopoda. The 'chydorid' lin e (basically the former family Chydoridae) is classified as a superfamily ( the Eurycercoidea), with three families; the 'macrothricid' line is capped by the superfamily Macrothricoidea, with four families. Of these seven fami lies, four are upgraded from subfamily status, the Chydoridae are left stat us quo, the Macrothricidae are redefined, and the Neothricidae are a new fa mily. The Macrothricidae are further subdivided in two subfamilies, of whic h the Macrothricinae appear reasonably homogeneous (monophyletic), while th e non-Macrothricinae require further study. Some of these (e.g. Guernella) have almost completely lost their P5, a situation parallel to that of the P 6 in the Eurycercidae, Acantholeberidae, and Ophryoxidae.