Revision of Heterocloeon McDunnough (Ephemeroptera: Baetidae)

The North American genus Heterocloeon McDunnough is redefined and shown to be distinct from other two-tailed Baetis complex genera, including Acentrella Bengtsson and Plauditus Lugo-Ortiz and McCafferty, which are also represented in North America. Heterocloeon is divided into three distinct subgenera, including Heterocloeon s.s., Iswaeon McCafferty and Webb, new subgenus, and Jubilatum McCafferty and Jacobus, new subgenus. Cladistic analysis supports the recognition of these subgenera within a genus defined by the presence of an apomorphic secondary ridge or denticle row on the larval claw; Heterocloeon s.s. and Jubilatum being sister groups, with their stem and Iswaeon branching basally within the Heterocloeon clade. The subgenus Heterocloeon, which possesses larval prothoracic osmobranchiae, retains the traditional species makeup of the genus. Iswaeon, which possesses a basally narrowed labial palp segment 2 and tibiae, and primary claw denticles of subequal length, includes a revalidated H. anoka (Daggy); H. davidi Waltz and McCafferty, new species; and H. rubrolaterale (McDunnough), new combination. Jubilatum, which posssesses an adenticulate secondary ridge on the claws and specialized tibial setation, includes H. amplum (Traver), new combination, and H. grande (Wiersema and Long), new combination. Previous confusion of H. anoka and Plaudituspunctiventris (McDunnough) is also resolved, with adult color patterns in Iswaeon and Plauditus shown to be of diagnostic importance.