THE ULTRASTRUCTURE OF THE CUTICLE OF NEMATODA .2. THE CEPHALIC CUTICLE OF STILBONEMATINAE (ADENOPHOREA, DESMODORIDAE)

The ultrastructure of the cephalic cuticle of 6 of 7 representative ge nera of Stilbonematinae (Eubostrichus, Catanema, Laxus, Robbea, Lepton emella, Stilbonema) is investigated using SEM and TEM techniques. Addi tionally, one species of Spirinia (Spiriniinae) and one of Desmodora ( Desmodorinae) were studied for outgroup comparison. Most of the studie d species show modifications of the cephalic cuticle. Furthermore, at least four different pathways have been developed to reinforce the hea d within Stilbonematinae. Species with a coarsely annulated somatic cu ticle (Leptonemella sp., Stilbonema majum, and Desmodora ovigera) deve loped a rigid, non-annulated cephalic capsule by modifying the main co nstructing element of the median zone, the ''ring body.'' In faintly a nnulated Laxus oneistus, the annulated cephalic capsule results from a newly inserted ''block layer'' between the median and basal zone. The non-annulated cephalic capsule of Robbea sp. is formed by both the bl ock layer and the ring body element. The annulated capsule of Catanema sp. stems from a doubled number of fiber layers within the basal zone . In Spirinia sp., only the amphidial region is strengthened in what c ould be termed an amphidial shield. All forms with cephalic capsules s how mechanisms to keep the oral region pliable. Only Eubostrichus topi arius lacks a reinforcement of the cephalic cuticle. A comparison with the literature is made to elucidate corresponding structures within t he cephalic capsules of representatives of Desmodorida. It is demonstr ated that the presence of a cephalic cuticle is of no systematic value above the genus level.