Revision and phylogeny of Myolaimus (Secernentea, Nematoda)

The four new species Myolaimus cotopaxus sp. n., M. hermaphroditus sp. n., M. hortulanus sp. n., M. xylophilus sp. n. and an unnamed fifth one are described from different habitats. Cross-breeding experiments for three very similar species revealed that they are distinct. The stemspecies pattern both of the Myolaimidae and of Myolaimus is reconstructed. This pattern allows for critical comments on and reinterpretations of descriptions of the nine Myolaimus species known from the literature. In the descriptions, only those characters are mentioned that are divergent from the stemspecies pattern of Myolaimus. A pictorial identification key is presented for all 14 species. One species is hermaphroditic, one other is phoretic. Spermatozoa are significantly smaller in the hermaphrodite as compared with in males of the gonochoristic species. Different molecular analyses do not propose a coherent taxonomical position of Myolaimus within the Secernentea. Morphological arguments are presented to show that Myolaimus and Deleyia are
sistergroups; and both are placed in Myolaimidae, a taxon grouped within Secernentea as incertae sedis.