Nematodes and Their Allies

Abstract

The relationship of nematodes to other organisms remains unclear even after 100 years of zoological arguments. Nematodes have been assigned to no less than four phyla. Perhaps the most generally accepted has been that of Aschelminthes, Grobben 1909. This group, adhered to by Hyman, includes 6 classes: Rotifera, Gastrotricha, Kinorhyncha (Echinodera), Priapulida, Nematoda, and Nematomorpha. The Priapulida, because their musculature is longitudinal and circular and because of variations in their body cavity, have been excluded from the phylum Aschelminthes. In other schemes, nematodes are placed in the phylum Nemathelminthes, which generally includes just the Nematoda and Nematomorpha, thus leaving Aschelminthes to hold Rotifera, Gastrotricha, and Kinorhyncha. In this text I will hold to the concept that nematodes belong in a phylum of their own, Nemata, as first proposed by Cobb in 1919, and reinstated by Chit-wood in 1958; and that each of the so-called related groups, that is, rotifers, gastrotrichs, kinorhynchs, and nematomorphs, are to be placed in their own separate phyla.