Question
Mon October 29, 2012 By:

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?

Expert Reply
Tue October 30, 2012
The name Protochordates literally means 'the first chordates'. Protochordates may not have a proper notochord present at all stages in their lives or for the entire length of the animals. They are all marine and small sized animals without true brain or skull. They lack jaws altogether. Also paired appendages are absent. Peculiar type of embryonic development is found. Also head and exoskeleton are not found. Pharyngeal gill-clefts are permanent and endostyle is present.

The protochordates fall into two broad groups or subphyla - the Urochordata and the Cephalochordata.

Urochordata:

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

Cephalochordata:

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

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