PROGRESS IN PROTOZOOLOGY

220 W. MICHAJLOW
Continuous observation of individual cultures is most important in
all investigations, because there have been found many euglenids parasitic
in copepods which can have several free-living generations in
the aquatic environment; yet these euglenids remain obligate parasites
of copepods.
I cannot consider here the detailed procedures necessary for species
determination; they are described in numerous papers written by me
and my coworkers.
The general criteria to be employed in determining parasitic euglenids
are as follows: (a) the structure of parasitic and free-living forms
(in a life cycle); (b) details of the developmental cycle; (c) typical movement
of the parasitic and free-living forms; (d) host specificity based
on statistical data; (e) geographic distribution.
Naturally, each of the foregoing categories entails more detailed
characteristics. For example, as far as structure is concerned, one can
differentiate 15 characteristics of the parasitic forms and an equal number
of characteristics limited to the free-living species. Among others,
the important characteristics include the type of the mastigont or of paramylon
(number, shape, etc. of the paramylon inclusions).
In the course of the developmental cycle, one should consider the
method of entry into the host and the site within it (e.g., intestine, body
cavity, ovum), the method of leaving the host, the ways of multiplication,
and the period of each phase of the developmental cycle, etc. — a
total of 25 characteristics. The characteristic movement of the parasitic
and free-living forms is difficult to describe; it can be best demonstrated
by cinemicrography. One can differentiate several degrees of hostparasite
specifity, ranging from very wide to quite narrow. The differences
in the degree of specificity depend upon geographical, ecological,
and even phenological factors.
Some other criterions of distinguishing the taxonomic units of
Euglenida, e.g., biochemical and enzymatic properties, which undoubtedly
will be taken into consideration in the future. Naturally, the aforementioned
characteristics have varying values in differentiating families,
genera, and species. For example, the general structure of the
mastigont is important in differentiation of suborders and paramylon
in that of species.
The parasitic Dinema (Heteronematina) have different developmental
cycles. In this instance parasitism has been the main factor in speciation
as well as in micro- and macroevolution. In this suborder we
find genera, e.g., Dinemula, Dinemina, Paradinemula, and Mononema,
containing only parasitic species.
In the suborder Euglenina there is the family Parastasiellidae consisting
of 11 exclusively parasitic species.
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