Animal Diveristy III: Craniata
This week we will finish our sampling of animal diversity with the Craniata. Consider
many of the trends you have already seen in organisms with bilateral symmetry. In this
clade you will see increased cephalization. Our focus this week is on the Vertebrata.
Some of the salient points to consider when making observations in this lab are:
adaptations associated with the water to land transition, feeding morphology, and
changes in limb morphology.
Craniata (Hagfish and Vertebrates)
The Craniata includes nine extant clades. Six of these (Myxini, Cephalaspidomorphi,
Chondrichthyes, Actinopterygii, Actinista, and Dipnoi) are collectively called “fishes.” The
other three classes (Amphibia, Sauropsida [which includes the subclass Aves], and
Mammalia) are the tetrapods and are primarily terrestrial. The common names for the six
fish clades are hagfish, lampreys, cartilaginous fishes, ray finned fishes, lobe‐finned fishes,
and lungfishes. This week’s lab will include hagfish and lampreys. We will examine the other
groups in the third lab on animal diversity.
subphylum vertebrata has
included the hagfish. This
creates on small problem:
the hagfish do not have
true vertebrae. As a result,
the term “Craniata” is used
to designate a larger clade
which includes the
vertebrates, along with
hagfish. The craniates are distinguished by having a cranium: a skull made of cartilage or
bone that protects the brain. Vertebrates can then be classified as animals with a backbone
composed of vertebrae.
Craniates also share the character of neural crest tissue, the chunk of neural ectoderm that
rolls up to form the dorsal nerve tube. Craniate embryos form this neural crest tissue, and
no other animal group does. The brain tissue develops embryologically to form just about
the entire vertebrate head, including most of the brain, the central nervous system, the
brain case, most of the sense organs, cartilaginous gill arches (which becomes parts of the
circulatory system, middle ear bones, and jaws), and teeth.
Characteristics of Vertebrates
Traditionally, the subphylum vertebrata has included the hagfish and lampreys. This creates
on small problem: the hagfish and lampreys do not have true vertebrae. As a result, the
term “Craniata” is used to designate a larger clade which includes the vertebrates, along