Subphylum: Cephalochordata

Classification of Animal Chordates of Class 11

Body fish-like adapted for burrowing and swimming. It lacks head, but possesses a tail.
Paired appendages absent, median fins (dorsal, ventral and caudal) are present.
Notochord extends the entire length of the body and passes ahead of the nerve cord in front. Notochord persistent throughout life.
A true enterocoelous coelom is present. It is however reduced in the pharyngeal region of atrium.
Digestive tract complete; circulatory system closed; heart and respiratory pigments are wanting.
Pharyngeal gill-slits more numerous and better developed.
Brain is indistinct; no paired sense organs - eyes, ears, nares.
Excretory system includes paired protonephridia with solenocytes.
Myotomes are the segments of muscles.
Sexes, separate; fertilization external; holoblastic segmentation.
Larva undergoes progressive metamorphosis. e.g. Branchiostoma (Amphioxus).

Fig. Branchiostoma : Entire animal in right side view