Analyses of SSU rDNA of 31 caligid taxa. Maximum likelihood (ML) phylogeny of the Caligidae based on 1685 characters of aligned SSU rDNA sequence data. The three Pseudocaligus spp. are placed in the Caligus clade (blue box), although support for the overall grouping is low. Pseudocaligus brevipedis is robustly supported (node a) in a clade with C. centrodonti and C. curtus that form a basal clade in the Caligus group. Pseudocaligus fugu is moderately well supported, from node b, as a member of the Caligus elongatus-like clade (red box) within the larger Caligus grouping. Pseudocaligus uniartus is well supported forming a sister clade with Caligus sp. 1 to the C. elongatus-like clade. All but one Lepeophtheirus spp. form a very robust clade, Lepeophtheirus clade (green box) from node c, which forms a consistent but poorly supported sister clade to the Caligus group (blue box). However, L. natalensis (highlighted) does not group with other Lepeophtheirus spp. and forms an unsupported branch at the base of the Caligus clade. Numbers in parentheses after specific names in the Caligus clade denote recorded sizes of adult female copepods from the literature [1, 22–24]. Numbers at the nodes represent branching support using non-parametric bootstraping (ML 1000 replications) and Bayesian posterior probabilities. Nodes with a bootstrap support of <50 and Bayesian posterior probability <0.95 were considered not supported (ns). Dissonus manteri is used as an outgroup and to root the tree.