Neotropical Monogenea. 7. Parasites of the Pirarucu, Arapaima gigas (Cuvier), with discription of two new species and redescription of Dawestrema cycloancistrium Price and Nowlin, 1967 (Dactylogyridae: Ancyrocephalinae).
Dawestrema cycloancistrioides n.sp., D. punctatum n.sp. and D. cycloancistrium are reported and described from A. gigas collected from the River Solimões, Amazonas, Brazil. D. cycloancistrioides most closely resembles D. cycloancistrium but differs by having a smaller body (1015 to 1766 µm long, 73 to 110 µm at widest point), a vaginal tube without a tight proximal coil, a short anteromedial process of the ventral bar, robust hooks (except pair 5), anchors of a different morphology and a short proximal egg filament. D. punctatum differs significantly from both D. cycloancistrium and D. cycloancistrioides in the comparative morphology of the haptoral armament (the anchor points have recurved tips), copulatory complex, vagina and egg. It comes closest to D. cycloancistrioides in the similar nature of the superficial roots of the anchor bases. An emended generic diagnosis is presented incorporating new information on the internal anatomy and structure of the copulatory complex and haptor. A summary of helminth species reported from A. gigas is provided.