Nicascolaimus punctatus gen. et sp.n. (Axonolaimidae) from an Australian beach links the families Axonolaimidae and Comesomatidae, mainly by the combination of a long conical stoma, loopshaped amphids and a punctate cuticle with ring pores. The anterior and posterior testes and the respective spermatozoa are very different in structure. The occurrence of sperm dimorphism in aquatic nematodes is reviewed, and new observations on Axonolaimus helgolandicus Lorenzen,
1972 and Microlaimus aff. paraborealis Allgen, 1940 are communicated. Particular reference is made to the peculiar spermatogenesis in Rhahdodemania species (Enoplida), resulting in three different structural types filling the vesicula seminalis.