PROGRESS IN PROTOZOOLOGY

PHYLOGENETIC RELATIONSHIPS AMONG PROTOZOA 205
7. Should the nassulids be considered as more closely related to the
tetrahymenids, since their oral structures are similar? One is inclined
to argue against this because oral structures have a higher probability
of being convergent and because the somatic cortical ultrastruetures of
nassulids place them more closely to the peniculines and microthoracines
than to the tetrahymenines (Lynn 1981, Small and Lynn
1981);
8. Should the apostomes be removed from KINETOFRAGMINOPHO-
REA? Small and Lynn (1981) have argued that this class is not
a natural assemblage and should, therefore, be abandoned. Moreover,
they related the apostomes to the oligohymenophoreans, because of the
resemblance of their somatic cortical ultrastructure;
9. Are toxicysts a phylogenetically important character, since Protocruzia
apparently has toxicysts? Toxicysts cannot be used as an important
diagnostic feature, but they do probably suggest a general common
ancestry of larger assemblages of ciliates.
Dr. Lynn has attempted to reply to as many of the questions
raised by Prof, de Puytorac as our knowledge at present allows.
Answers to questions pertaining to the morphogenesis of budding in
suctorians as indicating true diversity, the retention of stichotrichine
and sporado-trichine hypotrich groups, or the maintenance of a firm
division between pleuronematine and philasterine scuticociliates must
await more detailed comparative studies of all these groups.
Prof, de Puytorac has left a most stimulating question to the
end. Should the pattern of stomatogenesis always have priority over the
pattern of the differentiated oral structures? The speaker would tentatively
say yes, although a definite answer requires further, more detailed
treatment. Small (1976) has used this approach in establishing
the two subphyla; he considered the pattern of differentiation or dedifferentiation
of the cytopharynx to be extremely significant. Clearly,
this is an area where future discussion is warranted.
The discussant, Prof. CORLISS made the following comments. Dr.
Lynn has summarized well most of the principal problems facing ciliatologists
today who' have an overall interest in the phylogenetics and
evolution of the major groups comprising the phylum CILIOPHORA.
He has nicely included the controversial questions posed by Prof, de
Puytorac, who is sorely missed, in his printed abstract. In fact,
based mainly on the recent ideas and conclusions of E. B. Small and
Lynn, some still unpublished, Dr. Lynn has offered a new scheme
of classification of the ciliates that is, at the very least, stimulatingly
provocative.
We have come a long way from the times when the structural diversity
and topological distribution of the external ciliature, viewed solely
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