PROGRESS IN PROTOZOOLOGY

198 B. M. HONIGBERG
1. Morphological, especially fine-structural, features are, as indicated
by Prof. Scholtyseck, the principal bases for separation of
the higher protozoan taxa. It is the presence of the apical complex
that helps in placing a newly discovered organism in the phylum API-
COMPLEXA. This structural characteristic can be recognized rather
quickly. On the other hand, finding all stages of a life cycle might take
months, years, or, indeed a lifetime of an investigator;
2. It is now generally accepted that the main, or even the only
structural pattern found among the members of the phylum APICOM-
PLEXA is the one characteristic of the class SPOROZOA Leuckart,
1879, or even of the suborder EIMERIINA Léger, 1911. This limited
view can be seen in the diagrams of the apical complex included in the
majority of the more recent reports. The presence or absence of the
•conoid or the number and position of rhoptries and of subpellicular
microtubules are the features often used for separation of the members
of the phylum under consideration. However, this approach is not rational.
The structural organization may vary far more, e.g., Dermocystidium
marinum or Spiromonas. Yet the presence of a trilaminar pellicle,
or a micropore, or rhoptries etc. can be considered sufficient for inclusion
of an organism among APICOMPLEXA, even though any of these
structures by itself may not constitute sufficient grounds for assigning
a protozoon to SPOROZOA;
3. Dissimilarity in life cycles of organisms having similar structure
does not preclude their assignment to APICOMPLEXA. For example,
until the late 1960's or early 1970's the life cycles of genera such as
Toxoplasma, Sarcocystis, or Besnoitia were considered as distinct from
those typical of SPOROZOA. The more recent fine-structural findings
indicated the need for inclusion of these genera in APICOMPLEXA,
albeit not in SPOROZOA. Subsequent studies of their life cycles showed
that Toxoplasma and the related genera belonged together with Eimeria,
Isospora, and Plasmodium in the order EUCOCCIDIIDA Léger et Dubosq,
1910; they are considered now as members of the suborder EIMERIINA
Léger, 1911.
According to Dr. Beyer, the situation cited by her for Toxoplasma
may apply also to Dermocystidium (= Perkinsus) marinum, the life cycle
of which is incompletely understood. Thus, it is impossible to include
the latter genus in SPOROZOA. However, the presence of apical structures
in Perkinsus, although strikingly different from those of "typical"
coccidia, provides a sufficient reason for placing this organism in API-
COMPLEXA. Further studies are needed before a definite position in
this phylum is found for the heretofore neglected genus Perkinsus. The
discussant expressed no opinion about placing this genus in L e v i n e's
(1978) class PERKINSEA. (It should be noted here that several of the
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