Major study on the comparative anatomy of the mesosomal organs of scorpions concludes that the family Microcharmidae is synonymous with Buthidae

Volschenk, Mattoni & Prendini has now published a major review on the comparative anatomy of the mesosomal organs of scorpions (the mesosoma is the main body of scorpions where most internal organs are located). Todays scorpion systematics is mainly based on external morphology, and one of the aims of this study is to properly map the anatomy of several important internal organs and see if the anatomy/morphology of these organs can be used as characteristics in scorpion systematics.

One immediate result of this study is that there is support to say that the genera and species of the family Microcharmidae belong to the family Buthidae and that the data in this study don't warrant continued recognition of Microcharmidae.

Microcharmidae Lourenco, 1996 = Buthidae C. L. Koch, 1837

The following genera and species are transfered to Buthidae:

Microcharmus Lourenço, 1995
M. bemaraha Lourenço, Goodman & Fisher, 2006*
M. cloudsleythompsoni Lourenço, 1995
M. confluenciatus Lourenço, Goodman & Fisher, 2006*
M. duhemi Lourenço, Goodman & Fisher, 2006*
M. fisheri Lourenço, 1998
M. hauseri Lourenço, 1996
M. jussarae Lourenço, 1996*
M. maculatus Lourenço, 1996
M. madagascariensis Lourenço, 1999*
M. pauliani (Lourenço, 2004)*
M. sabineae Lourenço, 1996
M. variegatus Lourenço, Goodman & Fisher, 2006*
M. violaceous Lourenço, Goodman & Fisher, 2006*

Neoprotobuthus Lourenço, 2000*
N. intermedius Lourenço, 2000*

Here is the abstract from the article:

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.

References:
Volschenk ES, Mattoni CI, Prendini L. Comparative anatomy of the mesosomal organs of scorpions (Chelicerata, Scorpiones), with implications for the phylogeny of the order. Zoological Journal of the Linnean Society. 2008;154(4):651-75.[Subscription required for fulltext]

Family Buthidae