You report that “the sea squirt has the beginnings of a spinal cord, making it a so-called chordate.” That’s the same mistake I fight against each time I teach my zoology class. What makes a sea squirt a chordate is the notochord in the animal’s larval stage. A notochord is a skeletal component, not a primitive nerve cord.
J. Roger Eagan Queensbury, N.Y.
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