At the joint meeting of the 8th International Coccidiosis Conference and the Annual
Scientific Meeting of the Australian Society for Parasitology in Palm Cove, Australia,
in July 2001, a Controversial Roundtable was held on 'New classification of coccidia'.
The aim of this Roundtable was to stimulate and encourage discussion and debate on
current classification schemes for the group of parasitic protozoa known as the eimeriid
coccidia. In the past, such classifications have been based only on phenotypic characters
such as morphology, ultrastructure, life cycles, and host specificity. However, over
the past 10-15 years, molecular phylogenetic studies on taxa of the eimeriid coccidia
have revealed that several of the families, subfamilies, and genera that have been
erected based on non-molecular characters are paraphyletic. Therefore, this Roundtable
was an important forum for initial discussions on how a new and more comprehensive
classification of the eimeriid coccidia, which takes into consideration both phenotypic
and molecular characters, can be devised. The stimulus came from invited speakers
who gave introductions into selected areas of taxonomy and classification. Following
these introductions, a more general discussion with the audience addressed potential
steps that may be taken in future work. This review is the immediate outcome of the
Roundtable. It describes advantages and disadvantages of the use of phenotypic or
molecular characters as the base for taxonomic schemes for eimeriid coccidia. It gives
specific examples for drawbacks of current classifications based only on phenotypic
characters as well as potential pitfalls associated with the use of only molecular
phylogenies. It addresses current controversies as well as rules of taxonomy and nomenclature
relevant for the eimeriid coccidia. Finally, it recommends the establishment of an
international group of scientists to meet on a regular basis, stimulate further discussions,
and give direction on how the final goal, i.e. a proposal for a revised, and widely
accepted, classification of the eimeriid coccidia, may be achieved.