The present paper is the first classification of the phylum Gnathostomulida, of which 18 genera and more than 80 species are known. Two orders are created, according to the absence (Filospermoidea) or presence (Bursovaginoidea) of a female bursa-vagina-system and paired sensory organs. The latter order is divided into two suborders: Scleroperalia (with a cuticularized bursa) and Conophoralia (with a soft bursa and giant sperm). Presently Filospermoidea comprise 2 families; and the Bursovaginoidea, 6 families. Gnathostomulid evolution, as suggested in this paper, can be characterized by the following trends: shortening of the body and rostrum proportions, differentiation of skin as well as epidermal inclusions and of paired sensory organs, concentration of pharynx musculature, lamellarization of jaws and row-like arrangement of teeth, differentiation of the basal plate, and a more permanent vagina. In the derived phylogeny, Haplognathia is the most primitive, and Austrognatharia the most advanced type. A hypothetical ancestral form is outlined and possible relationships briefly discussed. A complete and categorized bibliography is given. |
