Note 6 - What Is a Cichlid? The Technical Details
What Is a Cichlid? The Technical Details
A nontechnical introduction to cichlids is given elsewhere at this
site. Cichlids are often characterized as freshwater perchlike fishes that have only a single
nostril on each side, have a divided lateral line, and lack a subocular shelf, among other
features. Unfortunately, these characteristics do not a cichlid make, because they are
plesiomorphies - character states that are primitive with respect to cichlids. To be sure
you've got a cichlid, and to substantiate cichlids as a monophyletic group, you need to know
the synapomorphies, or shared derived characters, of cichlids.
The following five apparently independent internal characters, from the cranial muscles and
gill arches, are hypothesized to be synapomorphies of the Cichlidae, and provide rather
strong evidence that the family is monophyletic (Stiassny, 1981a: 309):
"The loss of a major structural association between parts A2 and
A of the adductor mandibulae muscle and the musculous
insertion of a large ventral section of A2 onto the posterior border of the
ascending process of the anguloarticular.
"The presence of an extensive cartilaginous cap on the anterior margin of each second epibranchial bone.