Gnathostomulida

species classification - University of Michigan Museum of Zoology

list of the numbers of taxa described - Texas A&M University

ITIS - taxonomy and nomenclatural information - Integrated Taxonomic Information System

taxonomic hierarchy - The Taxonomicon

IRMNG genera list

Tree of Life

species list

species inventory, checklist

European Register of Marine Species (web archive site)

Marietta College, Invertebrate Zoology - lecture notes