Revision of the Acanthostominae Poche, 1926 (Digenea: Cryptogonimidae).

The digenean subfamily Acanthostominae is redefined and revised. Those 36 species exhibiting (1) lateral, follicular vitellaria, (2) a prepharynx, (3) a spinose tegument, (4! tandem or obliquely tandem testes contiguous in the hindbody, (5) a preacetabular pit, (6) an acetabulum not associated with a ventrogenital pit, (7) ceca extending near the posterior end o(the body, (8) a spherical or subspherical ovary, located near to and anterior to the testes, (9) an immediately preacetabular genital pore, (10) a genital pore not located in the preacetabular pit, (11) cpitheliated esophagus and ceca, non-epitheliated prepharynx, (12) a Y- or V-shaped excretory vesicle with postacetabular bifurcation, and (13) a terminal oral sucker armed with a single row of spines all belong in the Acanthostominae. Acanthostomes and their relatives are considered members or the Cryptogonimidae. Neotropicotrema bychowskyi and Allomacroderoides lepisostei ate transferred to Perezitrema and, along with Perezitrema viguerasi, represent plagiorchiform rather than opisthorchiform digeneans. Available names serve to partition acanthostomes into six genera. Acanthostomum (s.s.) contains the species spiniceps, absconditum, knobus, niloticum, minimum, gnerii, astorquii, americanum, and megacetabulum. The speciespavida, caballeroi, marajoaru. and brauni comprise Caimanicoia. Gymnatrema contains two species, gymnarchi and pambanense. Eight species, coronarium, productum, vicinum, gonotyl, atae, elongatum, crocodili, and nicolli, comprise Proctocaecum. Alrophecaecum contains the species burminis, indicum, pakistanensis, slusarskii, proctophorum, asymmetricum, and sunhai. Lastly, Timoniella contains imbutiforme, praeterita, scyphocephala, loossi and unami, as well as a new species from Venezuela previously misidentified as Acanthostomum scyphocephalum. The new species has smaller oral spines and exhibits blindly-ending ceca rather than ceca opening to the exterior near the posterior end of the body like T. scyphocephala. Haplocaecum is a synonym oi Atrophecaecmn. Acanthostomum bagri is a synonym of A. absconditum, A. nuevoleonensis is a synonym of A. megacetabulum, A. acuti is a synonym of Caimanicoia marajoara, A. diploporum is a synonym of Proctocaecum coronarium, Atrophecaecum hindusthanensis and Acanthostomum (Alrophecaecum) alii are synonyms of Atrophecaecum burminis, and Timoniella atherinae is a synonym of T. praeterita. Acanthostomum spiniceps knobus is elevated to A. knobus based on shape and mean number of oral spines, and on body proportions. A replacement name, nicolli, is proposed for a species of Proctocaecum originally designated Acanthochasmus quaesitus, a nomen nudum. Paracanthostomum and Ateuchocephalus are most closely related to Atrophecaecum but their status is not completely resolved pending description of an undescribed species recently collected by another worker. Numerical phylogenetic analysis of all species based on 25 characters in addition to the 13 which characterize the subfamily as a whole suggests that each recognized genus constitutes a monophyletic lineage. Biogeographical and coevolutionary relationships predicted by the genealogical hypotheses indicate that acanthostomes originated as piscicolous parasites occurring throughout Gondwana prior to the Cretaceous and that adaptive radiation featured invasion of aquatic reptilian hosts, primarily crocodilians, in three major instances involving four acanthostome genera.