Molecular Phylogenetics and Evolution 35 (2005) 21–34
www.elsevier.com/locate/ympev
1055-7903/$ - see front matter 2004 Elsevier Inc. All rights reserved.
doi:10.1016/j.ympev.2004.12.019
Eccrinales (Trichomycetes) are not fungi, but a clade of protists
at the early divergence of animals and fungi
Matías J. Cafaro
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Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, KS 66045-7534, USA
Received 22 July 2003; revised 3 September 2004
Available online 25 January 2005
Abstract
The morphologically diverse orders Eccrinales and Amoebidiales have been considered members of the fungal class Trichomyce-
tes (Zygomycota) for the last 50 years. These organisms either inhabit the gut or are ectocommensals on the exoskeleton of a wide
range of arthropods—Crustacea, Insecta, and Diplopoda—in varied habitats. The taxonomy of both orders is based on a few micro-
morphological characters. One species, Amoebidium parasiticum, has been axenically cultured and this has permitted several bio-
chemical and phylogenetic analyses. As a consequence, the order Amoebidiales has been removed from the Trichomycetes and
placed in the class Mesomycetozoea. An aYnity between Eccrinales and Amoebidiales was Wrst suggested when the class Trichomy-
cetes was erected by Duboscq et al. [Arch. Zool. Exp. Gen. 86 (1948) 29]. Subsequently, molecular markers have been developed to
study the relationship of these orders to other groups. Ribosomal gene (18S and 28S) sequence analyses generated by this study do
not support a close association of these orders to the Trichomycetes or to other fungi. Rather, Eccrinales share a common ancestry
with the Amoebidiales and belong to the protist class Mesomycetozoea, placed at the animal–fungi boundary.
2004 Elsevier Inc. All rights reserved.
Keywords: Mesomycetozoea; DRIPs; Bayesian analysis; Ichthyosporea; Trichomycetes
1. Introduction
The Eccrinales have been placed in the class Trichomy-
cetes (Zygomycota), which are fungal associates of various
Arthropoda. The class has traditionally included four
orders: Amoebidiales, Asellariales, Eccrinales, and Harp-
ellales. This group of symbionts inhabits a wide range of
hosts—Crustacea, Insecta, and Diplopoda—in varied
habitats (marine, freshwater, and terrestrial). The order
Eccrinales is characterized by unbranched, non-septate,
multinucleate thalli, and sporangiospore production
(Figs. 1A–C and F). They live attached to the cuticle lining
of the digestive tract of their hosts by a secreted, basal
holdfast. Asexual reproduction is by sporangiospores,
which form basipetally from the thallus apex, a feature
found only in the kingdom Fungi. Sexual reproduction
has not been observed, except possibly in one species,
Enteropogon sexuale, where scalariform conjugation was
reported (Hibbits, 1978). The fact that the Eccrinales share
a very specialized ecological niche, the arthropod gut, with
a group of well-known fungi, Harpellales (Trichomycetes),
in combination with the paucity of distinctive morpholog-
ical characters, have been the key criteria used in their clas-
siWcation within the Trichomycetes. The Eccrinales is the
only order of Trichomycetes with marine representatives;
out of 17 genera, seven have species that inhabit crusta-
ceans that live submerged in seawater. The distribution of
the eccrinids ranges from tropical forests (White et al.,
2000) to hydrothermal vents (Van Dover and Lichtwardt,
1986). They inhabit arthropods in almost all parts of the
world in every habitat that is suitable for their hosts.
¤
Fax: +1 785 864 5321. Present address: Department of Bacteriolo-
gy, University of Wisconsin, 420 Henry Mall, Madison, WI 53706,
USA. Fax: +1 608 262 9865.
E-mail addresses: cafaro@wisc.edu, matcafaro@hotmail.com.
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