Comparative anatomy of the mesosomal organs of scorpions (Chelicerata, Scorpiones), with implications for the phylogeny of the order

We present a review and reassessment of anatomical variation in the ovariuterus (and associated follicles), digestive gland, and lateral lymphoid organs of scorpions, and discuss the contribution of these character systems to the understanding of scorpion phylogeny. New data, obtained using light microscopy, are presented from an examination of 55 scorpion species, representing most scorpion families, and are collated with observations from the literature. Six distinct types of ovariuterine anatomy are identified: five in the family Buthidae and one in the remaining (nonbuthid) families. The buthid genera Lychas C.L. Koch, 1845 and Rhopalurus Thorell, 1876 are exceptional in possessing multiple types of ovariuterine anatomy among the congeneric species studied. The presence or absence of lateral lymphoid organs appears to be phylogenetically informative: the organ is absent in buthids, chaerilids and Pseudochactas Gromov, 1998. Embryo follicle morphology appears to be phylogenetically informative within the superfamily Scorpionoidea Latreille, 1802, where it supports the controversial sister-group relationship between Urodacus Peters, 1861 and Heteroscorpion Birula, 1903. The mesosomal anatomy of Microcharmus Lourenço, 1995 (Microcharmidae Lourenço, 1996) is consistent with that of Buthidae C.L. Koch, 1837, and we therefore propose the following new synonymy: Microcharmidae Lourenço, 1996 = Buthidae C.L. Koch, 1837. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 154, 651–675.