Phylogeny of Selected Maxillopodan and Other Crustacean Taxa Based on 18S Ribosomal Nucleotide Sequences: A Preliminary Analysis

Abstract

Abstract Relationships among the following taxa were examined based on 18S ribosomal RNA and DNA nucleotide sequences: Branchiopoda (Branchinecta packardi) , Ostracoda (two podocopid species), Branchiura (Argulus nobilis) , Pentastomida (Porocephalus crotali) , Copepoda (Calanus pacificus, Macrocyclops albidus) , Thoracica (Balanus eburneus, Calantica villosca) , Acrothoracica (Trypetesa lampas) , and Decapoda (Procambarus leonensis, Callinectes sapidus). Phylogenetic relationships were inferred by maximum parsimony and results evaluated by bootstrapping. With Branchinecta packardi as an outgroup, the following tree was inferred: the first branch leads to a node that joins a pentastome, a branchiuran and the two ostracodes; the second branch leads to a node that has the two copepods as a sister taxon to a clade that includes the acrothoracican and thoracicans; the last branch leads to a node joining the two decapods. The analyses suggest: (1) acrothoracicans diverged very early from the cirripede line and are not derived from a lepadomorph‐like ancestor; (2) branchiurans are not related to either copepods or thecostracans but are closely allied with pentastomes; and (3) the Maxillopoda, broadly defined, is not a monophyletic taxon. These results differ from previous studies of these groups.