EchiothrixDivision. Thomas (1898b:397) explained why Echiothrix is the proper name and not Craurothrix, which he earlier proposed thinking Echiothrix was preoccupied. Based upon shared cranial features, Thomas (1898b) thought Echiothrix to be related to the Philippine Rhynchomys and placed them in the Rhynchomyinae. Later workers disagreed (see summaries in Musser, 1969b, 1990), and, except to recognize that Echiothrix is an Old Endemic of Sulawesi (Musser, 1981c), no one has discovered the closest phylogenetic ally of this highly specialized, terrestrial vermivore. Spermatozoal morphology resembles that of Margaretamys, Maxomys, and in some aspects even Rattus, but is ambiguous in illuminating phylogenetic alliances (Breed and Musser, 1991), as is the meager chromosomal data for the genus (Musser, 1990). External, cranial, and dental morphology reviewed by Musser (1969b, 1990).

Miller and Hollister (1921a) described two species in addition to E. leucura, but these were included in the latter by Laurie and Hill (1954) and Corbet and Hill (1992), although Musser and Carleton (1993) proclaimed that a revision of the genus is required to determine if N and C Sulawesian samples represent one or two species. Recent multivariate analyses and study of qualitative dental traits indicate that available samples represent two species: one in the NE tip of the N peninsula, the other on the NC part of the N Peninsula and in the central core of Sulawesi (Musser, ms). This biogeographic pattern, one species at the tip of the NE peninsula and a related species restricted to the north and western portions of the N peninsula and the C part of the island, is common to species-pairs in several genera of endemic Sulawesian murines (for example, Taeromys, Rattus xanthurus Group, and Bunomys).