Kristian and I welcome the comments that were recently
posted by Ed Cutler.
The posting by Kirk Fitzhugh is a more than elegant
summary of what we were trying to do so we feel there is
nothing to add in that regard.
However, Ed's concerns should be addressed.
Nuchal Organs
We did consider giving the Sipuncula either their own state
for this character, or a score of 'present', but decided not to.
This was largely because, no matter what the innervation,
the structure is still single, hence not the same as the paired
structures found in virtually every group of 'polychaetes'.
This is a valid justification for our homology argument and
we made the term 'nuchal organ' restrictive.
However, for those interested in the 'what if' side of things,
coding the Sipuncula in our matrix with nuchal organs
present, ie. the same state as Polychaeta, or with their own
state 'single', does not change our trees; nuchal organs
merely appear independently for the Sipuncula every time.
This homoplastic result thus supports our narrow use of the
term. The issue of the 'Pogonophora' will be dealt with
further in forthcoming papers.
Longitudinal Muscles
Members of the Sipuncula, as we stated in our paper, can
have muscle banding but it does not resemble the situation
found in the Articulata. We had no reason to suggest any
homology and feel our coding is satisfactory on this point. In
fact Ed's comment that banding has evolved several times
in the Sipuncula provides further support for our decision to
regard the plesiomorphic condition for the group to be
'unbanded'. Coding Sipuncula with bands present will
collapse our trees and the heuristic value of this is difficult to
see.
Ed's comment that the banding found in Articulata could
have evolved several times within the group is problematic.
There are no taxa in the clade, to our knowledge, that have
an unbanded condition so we have no evidence for any
such speculation. Also, functional considerations of the type
suggested by Ed are untestable and we deliberately left out
any discussion of the many 'stories' about evolution in the
Metazoa. We suggest it is time to move beyond such a
methodology since it is largely responsible for the mess we
are in now.
Finally we are sorry we did not see Ed's fine book in the
course of our work and will certainly consult it in future.
greg and kristian
ps. We are not so confident in our result to suggest a
renaming of Annelida discussion group.
