Described as a grapsoid crab endemic to the Estelline Salt Spring near Estelline, Texas, Hemigrapsus estellinensis Creel, 1964 has long been regarded as an enigmatic taxon representing a small, now extinct, population of unexplained origins. At the tine of its description from the panhandle region of Texas, the species was acknowledged to be of close relationship to the North American Pacific coast species. H. oregonensis (Dana, 1851), from which it was reported to differ in relatively few morphological characters. No hypotheses were offered to explain a potential common lineage, and none seemed plausible given the long historical separation of waterways that might have joined this isolated population with Pacific congeners. We have examined morphology of archived type specimens of H. estellinensis and successfully sequenced the DNA barcode region of COI from one of the paratypes. Morphological and molecular genetic comparisons were made to selected congeners. We conclude that the Estelline Salt Spring population represented an introduction of H. oregonensis, and that H. estellinensis should hereafter be regarded as its junior synonym. Barnacles found in Estelline Salt Spring at the time that the grapsoid crabs were collected are also now known to represent two North American Pacific coast species. Recollections by an elderly ranch hand from Estelline, Texas of the area in the early 1900s lead us to postulate that railway cargos of Pacific coast timber may have been the pathway for these introductions.
