An Updated Classification of the Recent Crustacea

what your sentence says. Second, just because one
clade in a comprehensive analysis does not find
wide favor does not necessarily call other aspects
of the analysis into question. [Editors’note: In our
penultimate draft, we criticized the recognition of
the Phyllopoda by Schram and Hof, and then used
that criticism to cast doubt on other of their findings
in that paper; this unfair criticism has since
been removed.] What the main conclusion of
Schram and Hof indicated was that the issue of
crustacean phylogenetic relationships has more
mileage in it before we hope to approach a solution.
That ought to be conveyed in your text at this
point.
Submitted by Frederick R. Schram,
Zoölogisches Museum, Amsterdam
BRANCHIOPODA AS PRIMITIVE
You state several places that you place the Branchiopoda
as the sister group to the remaining crustaceans.
This may be correct, but you mention no
arguments. The only possible arguments could be
characters shared by the remaining crustaceans that
would set the Branchiopoda aside. It is not enough
to state that they [look] very primitive and that
some of them look like some of the ‘Orsten’ fossils.
I agree, of course, that the branchiopods ARE indeed
some of the most primitive Recent Crustacea
we have, but this doesn’t automatically give them
sister group position to the rest (only synapomorphies
for the remaining ...,asmentioned above).
It is NOT difficult to imagine the branchiopods (or
the cephalocarids) placed a little bit up in the system.
It would only require that the primitive features
that they have are retained a couple of nodes,
and that those that actually are branched off first
(Malacostraca, Remipedia, whatever) have attained
their special modifications independently from other
Crustacea.
So, to summarize, the discussion of which Crustacea
is the most primitive to look at, and which is
the sister group to the rest, is a mixture of two
discussions which actually should be separate. The
two discussions have been treated as one when certain
other authors have been discussing the same
for cephalocarids and remipedes, I know, but it
does not make the discussion more sensible. I believe
plenty of examples could be mentioned where
the sister group to a larger group is far from being
the best candidate as the most primitive one. To
take an example from animals we are both interested
in: If for example notostracans are the sister
group to all the ‘bivalved’ branchiopods, it doesn’t
follow that they also are the most primitive. This
is the same story for the possible sister group to the
Crustacea. We should not exclude any of the derived
forms from having that honorary position.
Only synapomorphies uniting the rest can place a
taxon in this position.
My advice would be to skip the idea of branchiopod
as sister group to the rest, unless you provide
arguments. But of course, you should retain
the point of branchiopods being quite primitive
(based on similarities to certain ‘Orsten’ fossils),
but I think it is impossible and subjective to distinguish
between the branchiopods and the cephalocarids
in this respect. [Both] look like certain ‘Orsten’
fossils, and not least the cephalocarids. There
is not [an] objective way to say which is most primitive,
because it depends on the feature you focus
on. So, perhaps you should mention both taxa as
the best candidates to being ‘primitive’.
Also, I simply don’t understand how you can say
that we ‘are treating the class Branchiopoda as the
most primitive of the Crustacea’ when this is not
included in your classification. It sounds like you
don’t believe it enough to actually include it (by
finding a name for the rest). In my opinion, it contains
no information about primitivity to mention
it as the first of the classes in your classification.
Submitted by Jørgen Olesen,
University of Copenhagen, Denmark
BRANCHIOPODA
Elucidation of the relationships of the ‘‘cladoceran’’
and ‘‘conchostraca’’ branchiopods appears to have
reached what is doubtless a temporary impasse.
Morphology seems to be saying one thing, some
molecular evidence another. In morphology, the
‘‘cladoceran’’ orders differ much from each other,
and attempts to unite them are unsatisfactory. On
his own estimation, Olesen (1998), who would do
so, feels that the monophyly of the ‘‘Cladocera’’
‘‘may not seem well supported’’ by his cladistic
analysis. In fact, of five characters used in support,
three are wrong, one is of no significance, and the
other is but a small, to be expected, adaptive
change that could have happened more than once.
The four constituent groups, which merit ordinal
rank, differ from each other more than do the various
orders of the Copepoda. Although some copepods
are modified for parasitic habits, some representatives
of all orders retain various fundamental
similarities.
Olesen himself says that his analysis does not
support the ‘‘Conchostraca,’’ nor, incidentally, the
Spinicaudata, a well-defined component of that
group, especially if the divergent Cyclestheria is
segregated from it. Nevertheless, he unites the morphologically
diverse ‘‘cladoceran’’ orders with the
unsupported, and very different, ‘‘Conchostraca’’ as
the ‘‘Diplostraca,’’ which compounds the difficulties.
All the alleged synapomorphies of the ‘‘Diplostraca’’
are incorrect (Fryer, 1999b). Walossek’s
(1993, 1995) less detailed attempt to demonstrate
the same relationship fails for similar reasons.
The Spinicaudata was fully differentiated at least
as long ago as the early Devonian. Ephippia of even
extant genera of the ‘‘cladoceran’’ order Anomopoda
are known from the Lower Cretaceous, and
molecular evidence suggests that Daphnia originated
more than 200 My ago (Colbourne and Hebert,
Contributions in Science, Number 39 Appendix I: Comments and Opinions 103