Blues for the red oxyagrion: A redefinition of the genera acanthagrion and oxyagrion (Odonata: Coenagrionidae)

Abstract

Examination of diagnostic features for all known species of Acanthagrion and Oxyagrion shows color pattern alone not to be a reliable diagnostic character. Both genera are redefined based on morphological characters, and some color pattern characters which further aid in their diagnoses. A preliminary phylogenetic analysis indicates both genera are monophyletic. They are distinguished from other genera of neotropical coenagrionids by their decumbent cerci with a dorso-basal tubercle in males correlated with the presence of paired mesepisternal fossae in females. Acanthagrion and Oxyagrion can be unequivocally distinguished from each other by the minimum width of abdomen, shape of distal portion of genital ligula and position of lateral lobes of genital ligula relative to flexure in males, development of mesepisternal carinae and of dark mid-dorsal and humeral stripes in females, and ratio of caudal lamellae to abdominal length in ultimate larval instars. According to our redefinition we transfer A. ablutum (a ‘blue’ species), A. hermosae and A. imeriense to Oxyagrion, and O. egleri to Acanthagrion. The generic placement of ‘A.’ taxaense and ‘O.’ pseudocardinale is deemed doubtful. © 2008 Taylor & Francis Group, LLC.