Change in rank of Megaperidae (Trematoda) to Megaperinae within the Apocreadiidae and description of Haintestinum amplum n. g., n. sp.

Haintestinum amplum n. g., n. sp. is described from the scrawled cowfish, Acanthostracion quadricornis, collected in the Eastern Gulf of Mexico off Florida, USA. The new species is relatively large and shares characters of the Apocreadiidae and Megaperidae but conforms to the diagnosis of neither. It belongs in a new genus possessing a pharynx with lobed anterior margin and intestine terminating in paired ani, like in megaperids, and, when compared with apocreadiids, it shares important anatomical features, including an I-shaped excretory vesicle, canicular seminal vesicle, eye-spot remnants, and pretesticular uterus and lacks a cirrus and cirrus sac. The H-shaped intestine and large funnel-shaped oral sucker without a U-shaped sphincter encircling half the anterior aperture are the most notable diagnostic characters of the new monotypic genus. Additionally, the phylogenetic position of the Megaperidae is investigated for the first time, using analysis of partial 28S rDNA gene sequences from H. amplum, two species in the Megapera, Thysanopharynx elongatus, and previously published 28S sequences of species from members of the Apocreadiata, Haploporoidae, Lepocreadiata, and Opisthorchiata. The resulting analysis demonstrated a close relationship among the new genus and the three species of megaperids, and the megaperids were most closely allied with Schistorchis zancli of the apocreadiids. Moreover, we now consider Megaperidae as the subfamily Megaperinae within the Apocreadiidae.