California Biota Home Page....Animalia


Phylum

This is a large phylum, whose diverse membership extends from sea squirts to humans.  All chordates have, at some stage of their life, a notochord (a dorsal, cartilagenous support), a dorsal nerve cord, and pharyngeal slits (gill slits).  The phylum is divided into three subphyla:

Subphylum Cephalochordata (lancelets) - [Not treated in the  California Biota website].

Subphylum Urochordata (tunicates, ascidians, "sea squirts"). The free-swimming larvae of these peculiar orgnanisms possess a notochord, a dorsal nerve chord, pharyngeal slits, and a post-anal tail.  Once a tunicate larva settles onto suitable substrate, it undergoes a substantial transformation, growing into a sedentary, sac-like adult with few traces of its chordate heritage.  While both native and introduced tunicates can be found in California waters (indeed, they are common on pilings in San Francisco Bay), we plan to devote little space to them here in the California Biota website (unless, of course, a specialist offers to take on the challenge of providing such coverage).

Subphylum Vertebrata (fishes, reptiles, amphibians, birds, mammals).  In this familiar lineage of organisms, to which we belong, the notochord is replaced by bone, forming a rigid, articulated support that protects the dorsal nerve chord.