Please cite this article in press as: Brown, M.W., et al., A contemporary evaluation of the acrasids (Acrasidae, Heterolobosea, Excavata). Eur. J. Protistol. (2011), doi:10.1016/j.ejop.2011.10.001 ARTICLE IN PRESS EJOP-25227; No. of Pages 21 Available online at www.sciencedirect.com European Journal of Protistology xxx (2011) xxx–xxx A contemporary evaluation of the acrasids (Acrasidae, Heterolobosea, Excavata) Matthew W. Brown ∗ , Jeffrey D. Silberman, Frederick W. Spiegel Department of Biological Sciences, University of Arkansas, SCEN 601, Fayetteville, AR 72701, USA Received 11 August 2011; received in revised form 18 October 2011; accepted 19 October 2011 Abstract Sorocarpic protists are organisms that individually aggregate and work together to form a fungus-like fruiting body (sorocarp). The amoeboid forms are often colloquially referred to as “cellular slime molds” or “acrasids”. We argue the latter term should be used only to refer to members of Acrasidae in Heterolobosea. Here we study the diversity of two Acrasidae genera, Acrasis and the closely similar Pocheina, using a combination of morphological characteristics and small subunit rRNA gene sequences. A total of eight isolates of Acrasis and an example of Pocheina were examined. Acrasis/Pocheina form a well-supported monophyletic group that is the highly supported sister to a clade containing Allovahlkampfia and several other amoebae. Four molecular lineages of Acrasis were resolved, each of which is characterized by a distinctive fruiting body morphology. Each lineage represents a species, two of which are novel, Acrasis kona n. sp. and Acrasis takarsan n. sp. An isolate identified as Pocheina rosea is nested within the clade containing isolates of the taxon Acrasis rosea, into which P. rosea is tentatively subsumed. One member of the tightly knit allovahlkampfid clade was induced to form a simple sorocarp, leading us to include this clade in Acrasidae. © 2011 Elsevier GmbH. All rights reserved. Keywords: Sorocarpic protists; Cellular slime molds; Phylogenetics; Acrasis; Pocheina; Allovahlkampfia Introduction In the broadest sense, sorocarpic protists include a broad range of eukaryotic microorganisms that have a complex aggregative life cycle that may result in the formation a multi- cellular, propagule-dispersing structure, called a sorocarp or fruiting body (Brown et al. 2011). Those sorocarpic protists with amoeboid tropozoites have classically been called “cel- lular slime molds” (Bonner 1967; Olive 1975; Raper 1984) or “social amoebae” (Schaap et al. 2007); although, we argue ∗ Corresponding author at: Centre for Comparative Genomics and Evolu- tionary Bioinformatics, Department of Biochemistry and Molecular Biology, Dalhousie University, 5850 College Street, Halifax, Nova Scotia B3H 4R2, Canada. Tel.: +1 902 494 2881; fax: +1 902 494 1355. E-mail address: protist@live.com (M.W. Brown). that the term “sorocarpic amoebae” is preferable (Brown et al. 2011). Our concept of sorocarpic protists was originally derived from observations made by van Tieghem (1880) on an aggregating and fruiting amoeba he named Acrasis gran- ulata. van Tieghem (1880) discovered that the amoebae that make up the fruiting bodies of this organism retain their indi- viduality throughout the life cycle including in the sorocarp, whereas the fruiting bodies of the myxogastrids (sporocarps) are derived from a single, large, coenocytic amoeba, the plas- modium. The first sorocarpic organism actually described was Dictyostelium mucoroides; however, Brefeld (1869) mis- interpreted the life cycle as having a true plasmodium from which the fruiting body develops. Subsequent careful obser- vation by van Tieghem (1880) correctly determined that the “plasmodium” of Dictyostelium was actually the result of aggregation and was separable into individual cells when 0932-4739/$ – see front matter © 2011 Elsevier GmbH. All rights reserved. doi:10.1016/j.ejop.2011.10.001