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Fishes and Pisces
The rather handy polyphyletic term "fish" and it's
Latin counterpart (as Mike Keesey notes, not used very
often nowadays) is restricted to those craniates which
have scales, fins, "fish-heads", etc. all those
wonderful things you think of when you think fish --
but also think shark, eel, lampreys, hagfish....
Basal craniate phylogeny marks the separation of
hagfishes from the rest, then lampreys, (or both
together from the rest, depends on the various
phylogenies you look at; and no, I haven't done too
much looking here) then a few nodes up the line we get
the Chondrichthyes (cartilage-skeleton'd "fish" like
sharks and rays, but ... also other fish), which
includes Osteichthyes, the sister-group to the shark
et al. clade, which includes Actinopterygii, the
ray-fins, which include the Sarcopterygii, the
lobe-fins, which include the proto-tetrapods, and so
on up (like dipnoans, etc.): Dingus and Rowe 
and the Tree of Life homepage both offer accessible
phylogenies demonstrating this, and Mike Keesey's and
Jack Conrad's web sites also show these.
Polyphyletically, it's a mess to work with, and I
don't know what was on Karl von Linné's mind when he
comprised these groups, or his successors.
Jaime "James" A. Headden
"Come the path that leads us to our fortune."
Qilong---is temporarily out of service.
Check back soon.
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