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