A "real" conundrum (Opabinia)

[Ken Kinman]

Dear All,
      The taxon _Opabinia_, a name attached to a "real", apparently 5-eyed,
Cambrian animal, has fascinated me for many years.   But if it is a "form
genus", as I have suspected since first studying it in the 1980's, every
cladistic analysis that assumes it is a distinct animal will be seriously
flawed (making the overall systematics of arthropods and their relatives
more difficult than it already is).
      I am throwing out this hypothesis, that it is a "form genus" (larval
form or dwarf male), however silly some people may find it, so that it can
be discussed (and rejected if it lacks merit).
                         ----Ken Kinman
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             WHAT ON EARTH WAS OPABINIA???
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     In my 1994 book (The Kinman System), I created a new Class Anomalocarea
(within Phylum Arthropoda) consisting of two Orders: Anomalocarida and
Opabiniida.   However, I noted that my first impression of _Opabinia_ (back
in the late 1980's) was that it is a possible immature (i.e. larval) form of
Anomalocaris, and therefore I have never seriously questioned IF they are
related, but only how CLOSELY related.
     The purpose of this posting will be to suggest  alternatives to the
traditional view (the latter reflected in hypothesis 1), particularly my own
strong suspicion that Opabinia may well be a "form genus" (either a larval
or dwarf male form of anomalocarid; hypotheses 2 and 3). Presently I have
three main possibilities to explore:
          (1) They are only closely related enough that they should continue
to be classified as separate Orders in a Class Anomalocarea (the
conservative viewpoint reflected in my formal classification of 1994).
          (2) Opabinia is an immature (larval) form of anomalocarid, and
that Opabiniida therefore should be placed as a synonym of Anomalocarida.
          (3) Opabinia is the dwarf male form of Anomalocarids, which also
makes the two orders synonymous.
      I presently would give Hypothesis 2 the highest degree of probability
(perhaps 49%), followed by Hypotheses 1 and 3 (25% probability for each),
and only a 1% probability that they are so unrelated that they must be
placed in separate phyla (a probability so low that I do not presently
believe it merits being listed as a fourth "main" possibility).  Of course,
I might eventually transfer Class Anomalocarea to Phylum Protarthropoda or
an aschelminth phylum, but wherever they go, Anomalocarids and Opabinia
belong together in my opinion.  I never understood Whittington's insistence
that they were unrelated (but hopefully he has reconsidered).
      Therefore, grouping together Hypotheses 2 and 3, I would presently
give a 74% probability that Opabinia is simply a variant form (male or
larval) of Anomalocarid.  If this is true, then I would expect such
"opabiniid" forms to vary somewhat, depending on which Anomalocarid genus
they belong to, but that these differences may well be less distinctive than
the differences in the corresponding adult females of various anomalocarid
genera.   If my hypothesis is shown to lack merit, I will abandon it.
Criticism is welcomed.
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                     ----Kenneth E. Kinman
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