Nematodes

Name

Greek: nema = filament, zoon = animal.

Synonyms

Roundworms; Threadworms

Classification

Phylum of Metazoa, group of Ecdyzoa.

General Information

The nematodes are elongate worms ranging in length from 0.3 mm up to the 8.5 m of Placentonema gigantissimum in the placenta of whales; they may inhabit soil, freshwater, and saltwater habitats and are frequently encountered as parasites of plants, humans, or animals. In general, they are dioecious and in many species clear sexual dimorphism exists (Fig. 1, Hookworms/Fig. 1). Males are usually smaller than females (Table 1); both may have copulatory organs. The bilaterally symmetrical body of the unsegmented nematodes is covered by a typical cuticle which is formed by a hypodermis and must be shed during molt (Fig. 2, Ecdysis). The pseudocoelomatic body cavity of adults mostly contains a complete digestive tract, the anus of which is subterminally situated (Figs. 1 and 3).

Fig. 1

Diagrammatic representation of the posterior ends of...