A new species of Spirorchis MacCallum, 1918 (Digenea: Schistosomatoidea) and Spirorchis cf. scripta from chicken turtle, Deirochelys reticularia (Emydidae), with an emendation and molecular phylogeny of Spirorchis.

Chicken turtles, Deirochelys reticularia (Latreille in Sonnini et Latreille) (Testudines: Emydidae) from Alabama, USA were infected by Spirorchis collinsi Roberts et Bullard sp. n. and Spirorchis cf. scripta. The new species is most easily differentiated from its congeners by the combination of having caeca that extend far beyond the genitalia, intercaecal genitalia positioned in the middle portion of the body, a testicular column that nearly abuts the caecal bifurcation, a cirrus sac positioned between the testes and ovary, a massive Mehlis' gland, an elongate, longitudinal metraterm that extends anteriad beyond the level of the ovary, a pre-ovarian genital pore, and a prominent, intercaecal Manter's organ. The specimens of S. cf. scripta differed from the holotype and published descriptions of Spirorchis scripta Stunkard, 1923 by several subtle morphological features, perhaps comprising intraspecific variation, but collectively warranted a detailed description herein. Based on examinations of the aforementioned specimens plus the holotype, paratypes and vouchers of morphologically-similar congeners, Spirorchis MacCallum, 1918 is emended to include the presence of oral sucker spines, a pharynx, lateral oesophageal diverticula ('plicate organ') and a median oesophageal diverticulum ('oeseophageal pouch'). Phylogenetic analysis of the nuclear large subunit rDNA (28S) recovered S. collinsi sister to Spirorchis picta Stunkard, 1923, > 99% similarity between S. cf. scripta and S. scripta, and a monophyletic Spirorchis MacCallum, 1918. No blood fluke infection has been reported previously from these drainages, Alabama, or this turtle species. This is the first new species of Spirorchis to be described from North America in 26 years.