[Taxacom] Eumetazoan eyes

[Kenneth Kinman]

Dear All,
      In the thread on underlying synapomorphies, the vertebrate and
cephalopod eye was brought up.  It seems that the basic eumetazoan eye
type was established in the common ancestor of Cnidaria and other
Eumetazoans.  Similarilities between vertebrate and cephalopod eyes (or
some other eumetazoan eyes) are perhaps a combination of this initial
eumetazoan synapomorphy with some subsequent homplasies and/or more
complex synapomorphies.                 
      Therefore, saying that a given eumetazoan group has "complex" eyes
is phylogenetically not particularly useful.  It is the particular
subtype of complex eye that would be useful.  If you dig deeper, do
cephalopod eyes have more characters in common with arthropod eyes than
either of them have with vertebrate eyes?  Complex eyes are a very
complex combination of many simpler characters which should each be
scored separately in a cladistic analysis at Phylum level.  
         -----------Ken