Classification of protochordata
Answers
Explanation:
protochordates urochordates &chephalocordates
Answer:
Explanation:
1.Protochordates are commonly called lower chordates.
2.They lack a head and a cranium, so they are also known as Acraniata.
3.Protochordates consists of three sub-phyla based on the property of notochord. They are Hemichordata, Urochordata and Cephalochordata.
1. Hemichordata:
All hermichordates are marine. Some are solitary and slow moving, others are sedentary and colonial.
Body structure:
Body is stout and unsegmented, and has a worm–like or vase–like
Three distinct regions namely proboscics, collar and trunk are present.
They are bilaterally symmetrical and triploblastic.
They have organ-system level of organization.
2. Urochordata or Tunicata:
They are marine, mostly sessile, filter–feeders.
Body is enclosed in a leathery test or tunic sheath, composed of tunicin (cellulose) so called tunicates.
The notochord occurs only in the tail of larva and disappears in the adults called retrogressive metamorphosis.
The nerve chord (neural tube) is present in the larva, but is replaced by a single dorsal ganglion in the adult.
The gill slits or stigma are numerous, persist in the adults and open into the atrium, instead of opening to the exterior. There are no true gills but are called branchial basket.
Circulatory system is of open type. Blood consists of Venadocytes.
Excretory system is lacking.
Asexual reproduction occurs by budding.
3. Cephalochordata:
They are also marine and filter-feeders.
The notochord extends up to the cephalic or head region and persists throughout the life.
The nerve chord persists throughout the life, but no brain is formed.
Excretion occurs by solenocytes.
The gill slits are numerous and persist in the adults. They open in atrium and true gills are absent.
The body wall consists of myotomes.
Tail persists throughout the life.