Description of Heterosentis holospinus n. sp. (Acanthocephala: Arhythmacanthidae) from the striped eel catfish, Plotosus lineatus, in Halong Bay, Vietnam, with a key to species of Heterosentis and reconsideration of the subfamilies of Arhythmacanthidae

Heterosentis holospinus n. sp. is 1 of 11 species of acanthocephalans collected from 13 species of marine fish in Halong Bay, Vietnam, in 2008 and 2009. The striped eel catfish, Plotosus lineatus (Thunberg, 1787), harbored a large number of individuals of the new species. Species of Heterosentis Van Cleave, 1931, are characterized by having 2 or 3 types of proboscis hooks in 10-14 rows, and trunk spines. Of the 15 known species of Heterosentis (including the new species), H. holospinus is distinguished by having a trunk entirely covered with spines and an anterior trunk cone free of spines. Only Heterosentis overstreeti Schmidt and Paperna, 1978, has a trunk that is also entirely covered with spines; it, however, differs from H. holospinus by lacking an anterior trunk cone but having 4 giant nucleated muscle cells in the anterior trunk, and 2 basal spines per proboscis hook row. Heterosentis holospinus has no such muscle cells, and the proboscis contains 3-4 spines per row. Only 2 other species of Heterosentis have anterior trunk cones: Heterosentis septacanthus (Sita, 1949) Golvan 1969, which has a cylindrical trunk and proboscis, only anterior trunk spines, and smaller proboscis hooks, and Heterosentis plotosi Yamaguti, 1935, which has 4 nucleated giant muscle cells, only anterior trunk spines, and 4-5 spines per proboscis hook row. The characteristics of H. holospinus are described and compared with those of the other 14 species of Heterosentis. A key to the 15 species of the genus is included. The justification for the retention of the 3 subfamilies of Arhythmacanthidae no longer applies, and their deletion is proposed. © 2011 The Helminthological Society of Washington.