Partial re-assessment of the family structure of the Clausocalanoidea (Copepoda: Calanoida) using morphological data

A cladistic analysis of the non-Bradfordian' genera was used to improve the classification of the superfamily Clausocalanoidea. The prevalence of homoplasy among the morphological characters used interfered with tree inference and our assessment of support for the topologies produced. Characters previously thought to have phylogenetic significance appear to be homoplasious (e.g. the presence of large spinules on the coxa of leg 4). Other characters, not previously thought to have phylogenetic significance, contributed to the fundamental topology of the trees even though incompletely congruent. These female characters are the setation of: antennular ancestral segments I, XIII, XV, XXI and XXIII; mandible basis and endopod segment 1; maxillule exopod; the maxilla praecoxal endite 1; and segmentation of the leg 1 exopod and leg 2 endopod. Our phylogenetic hypothesis of the non-Bradfordian' Clausocalanoidea, using Bradfordian' taxa as the outgroup, gives some confidence in three clades: Aetideidae Giesbrecht, 1893, Clausocalanidae Giesbrecht, 1893 and Pseudocyclopiidae G. O. Sars, 1902, a conclusion requiring corroboration with genetic data. The Euchaetidae are always nested within the Aetideidae, and the Stephidae are paraphyletic and nested within the Clausocalanidae. The Mesaiokeratidae is a terminal branch within a clade composed of genera currently grouped as the Stephidae.