247produce free-swimming flagellate spores (zoospores) which are chemically attracted by the body excretions of nematodes. T h e zoospores swim towards the nematodes and encyst on to their surface, then penetrate and kill the nematode as a normal endoparasite. Because such species actively pursue, catch and kill nematodes, Barron ( 1 9 7 7~) has suggested that they could be classed as predators, but in terms of morphology and life-cycle they are included with the endoparasites. The genus Nematoctonus forms a bridge between the two groups, with some species predatory and others endoparasitic in habit. The predatory species capture nematodes by means of adhesive knobs growing directly from the hyphae, whereas in the case of the endoparasitic species of the genus, nematodes are captured by adhesive knobs that form on the conidia only, never on the hyphae.( I ) EndoparasitesEcology of nematophagous fungi 249 ( c ) Ingested conidia Some species of endoparasites have developed morphologically adapted conidia which, when eaten by the host, become lodged in either its buccal cavity or oesophagus. These species belong almost exclusively to the genus Harposporium, and the degree of adaptation is quite unusual. The conidia are crescent-shaped (Harposporium anguillulae), helicoid ( H . helicoides), or with irregular processes emerging from odd- shaped conidia ( H . diceraeum). After ingestion, the position within the gut in which conidia finally become lodged depends on the shape of the conidium, which is species-specific. For example, conidia can become lodged in the muscle tissue of the oesophagus ( H . anguillulae), travel to the lower gut ( H . arcuatum, H . helicoides, H . oxycoracum) or become anchored in the buccal cavity ( H . bysmatosporum, H . diceraeum). The conidia appear unaffected by being ingested by a nematode, and are resistant to the digestive enzymes produced by the animal. The crescent-shaped conidia of the most widely distributed and frequently isolated species H . anguillulae has one sharply pointed end.
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