Collar spine models in the genus Echinostoma (Trematoda: Echinostomatidae).

This paper discusses collar spine arrangements in the genus Echinostoma. All arrangements are of uneven numbers of collar spines on the oral collar. The total number of collar spines in these arrangements ranges from a low 31 to a high 51. There are 11 models of collar spine arrangements in the Echinostoma consisting of spine numbers 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, and 51. Representative species with these collar spine arrangements are given in the article. The number of collar spines in a species is identical in both the larval and adult forms. Reports of even numbered spine counts in the genus Echinostoma are erroneous and probably reflect counts on worms with lost, retracted, or supernumerary spines.