PROGRESS IN PROTOZOOLOGY

195
The foregoing subdivisions of APICOMPLEXA reflect Prof. S c h o 1t
y s e c k's belief that asexual reproduction, i.e., schizogony (or merogony),
represents a secondary development in the course of evolution
of the phylum found only in the more advanced intracellular SPORO-
ZOA. The more primitive gregarines and coccidia have only the sexual
reproductive phase.
According to the speaker, if one follows his approach to the taxonomy
of APICOMPLEXA, the genus Perkinsus Levine, 1978, the sole
member of the class PERKINSEA Levine, 1978, is to be considered not
as sporozoan, but as an apicomplexan. On the other hand, the members
of the order AGAMOCOCCIDIIDA Levine, 1979 do not belong among
COCCIDIA Leuckart, 1879.
A different approach to APICOMPLEXA was presented by the second
speaker, Prof. DESSER.
It was his understanding that the name APICOMPLEXA was
created by Levine (1970) to replace the older and generally employed
name SPOROZOA which included only the gregarines, coccidia, and
piroplasms. In addition to possessing the apical complex, as revealed
by electron microscopy, the majority of the species belonging to API-
COMPLEXA have life cycles that involve gamogony and sporogony;
in most instances they include also merogony.
The inclusion of the class PERKINSEA Levine, 1978 among API-
COMPLEXA (with the single genus Perkinsus Levine, 1978) in the most
recent scheme published by the Society of Protozoologists (Levine
et al., 1980) is not justified. Admittedly, the zoospores of this peculiar
organism possess certain features which superficially resemble the apical
complex. These features might have resulted, however, from convergent
evolution of organisms of different ancestry and function in a similar
manner to enable the parasites to assume their intracellular location.
Moreover, these parasites do not undergo sexual reproduction, sporogony,
or merogony. Finally, the zoospores of Perkinsus sp. (which are
not sexual stages) are biflagellate (Perkins 1976). For those reasons,
he felt that the class Perkinsea should be removed from the APICOM-
PLEXA and that the original concept of APICOMPLEXA as the equivalent
of SPOROZOA, be retained.
Prof. Desser felt that not enough information is available at this
time to justify definitive decisions with regard to the affinities of the
piroplasms. One must agree with him that much evidence was provided
during the Sixth Congress in support of this opinion. One of the
lines of evidence was the demonstration by Prof. V i v i e r that Dactylosoma
ranarum is an eimeriid coccidian rather than a piroplasm. Intraerythrocytic
merozoites of these species have a trilaminate pellicle, po-
http://rcin.org.pl