can u plz explain me what are meant by protochordates and their division of cephalochordata and urochordata?also try to give some of its charachteristics and examples?
The protochordates fall into two broad groups or subphyla - the Urochordata and the Cephalochordata.
The urochordata includes the group known as the tunicates. They are bag-like, sessile, soft-bodied and non-metameric. Adult body is covered by a tunic. Notochord is present in the tail of free-living tadpole like larva and is absent in the sessile adult. They are hermaphrodites and exclusively marine.
Example - Doliolum, Salpa, Herdmania
Cephalochordates are fish-like animals that are metamerically segmented and having a notochord and nerve chord along the entire length of their bodies throughout their lives. They possess post-anal tail and lack exoskeleton. Sexes are separate. They are marine and burrow in the sand of shallow sea-water. Cephalochordates also have a well-developed circulatory system but does not have a heart
Example - Branchiostoma, Asymmetron