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Largest of the deuterostome phyla. All the chordates possess three unique characteristics at some stage in their life history. These three diagnostic features are:
Phylum chordata is divided into two groups: Acraniata (Protochordata) & Craniata (Euchordata).
Acraniata : All marine, small, primitive chordates. Lacking a head, a skull or cranium, a vertebral column, jaws and brain. It is divided into three subphyla-Hemichordata, Urochordata and Cephalochordata chiefly on the character of notochord present (Recent opinion removes Hemichordata as a separate phylum of invertebrates).
Craniata : Includes single subphyla - Vertebrata. Divided into two subdivisions:
(a) Agnatha (Jawless vertebrates) : has two classes - Ostracodermi and Cyclostomata.
(b) Gnathostomata : Further divided into two superclasses :