A Eeview of the Copepod Genus Paranthessius Claus

The problem of arriving at a natural classification of the copepods has been in no small measure complicated by the repeated appearance within the group of the parasitic and commensal habit. In the cyclopoids, two sections, the Poecilostoma and the Siphonostoma, have been established and remain well differentiated on the basis of the specialization of mouth appendages correlated with parasitic and semiparasitic existence. Unfortunately for the systematist, these copepods seem to exhibit the widest tolerance in the selection of hosts. From the records, any phylum above the Protozoa which is represented to any conspicuous degixe in the marine fauna is likely to appear in the roster of hosts of cyclopoid symbionts. This diversity of occurrence, in addition to small size, inconspicuous appearance, and remarkable agility in eluding usual methods of capture, has resulted in a scattered and fragmentary representation of this group in museum collections and consequently in the literature on copepods. The most extensive reports to date either have been surveys of the faunas of fairly limited