Antennule development during copepodite phase of some representatives of Harpacticoida (Copepoda, Crustacea)

The copepodite antennule development of representatives of 6 harpacticoid families is studied and discussed in detail and that of 8 genera of harpacticoids from 7 families is schematically illustrated. Twenty-seven genera out of 17 harpacticoid families are compared on the basis of own investigations and data from the literature. The origin of newly formed segments can be determined by seta numbers of segments, relative segment length, furrows indicating previous articulations and by the position of the segment which bears the proximal aesthetasc. There are 2 zones of segment formation, both located in the middle part of the first antenna. Normal segment formation takes place distally from the second, aesthetasc-bearing segment from C I to C II and proximally of it from C III to C IV. At least in some species sexual dimorphism of first antennae is present from C II onwards. Females practically show the adult antennular state at C V whereas males undergo important changes from C V to C VI with proximal addition of segments, and often with distal fusions and formation of a unique armature due to adaptations in clasping behaviour. There are specific formation patterns in certain taxonomic groups. E.g. Harpacticidae, Canthocamptidae, Canuellidae and Longipediidae deviate in antennule formation from the rest of Harpacticoida. A higher number of antennular setae of C I which in most of the cases are reduced in C II may be interpreted as indicating an ancestral multisegmented antennule for Harpacticoida.