Somite size variation during copepodid development of podoplean copepods

Abstract

Abstract Reports of podoplean first copepodids with more or fewer than the ancestral two narrow somites are considered. On some poecilostomatoids, the fourth and fifth thoracic somites, and the anal somite appear narrow on the first copepodid. Further development of the body during the copepodid phase includes only transformations or additions of narrow somites. Some caligid siphonostomatoids also have the same three narrow somites on the first copepodid. Reanalysis of their copepodid development indicates not only transformations and additions of narrow somites but also the incorporation of broad somites into the cephalothorax, and a failure to form the middle and posterior limbless abdominal somites. Support for one narrow somite on the first copepodid is unconvincing.