(i) They are mostly marine called poikilothermic
animals (i.e., they have the capacity to regulate
their body temperature).
(ii) The body is laterally compressed and
spindle-shaped.
(iii) Notochord is persistent throughout the life.
(iv) Mouth is ventral in position, skin is tough containing
minute placoid scales and teeth are
modified placoid scales. They have strong jaw
are predaceous by nature.
(v) Gill slits are generally five pairs and gill cover
(operculum) are absent.
(vi) Heart is two-chambered with one auricle and
ventricle.