Question

Members of agnatha exhibit________

• A. migration to marine water
• B. similar exoskeleton like fishes
• C. similar circulatory system as that of earthworm
• D. sucking mouth with jaws

Answer 1

The correct option is C similar circulatory system as that of earthworm

Class vertebrata is further divided into two groups as Agnatha and Gnathostomata. Agnatha, also known as primitive fishes, have a circular mouth (Cyclostomata), not bounded by jaws. These are jawless fishes. e.g. Petromyzon, Myxine, etc.
Gnathostomata means mouth is bounded by jaws. This group is further classified into five classes as Pisces, Amphibia, Reptiles, Aves and Mammals.
Following are few important characteristics of Agnatha.

1. They have cartilaginous skulls and tooth-like structures composed of keratin.
2. True jaws are absent.
3. Paired fines are absent
4. The nostril is single and median.
5. Notochord present through life.
6. Heart is two-chambered.
7. Five to sixteen pairs of gills are present in sac-like pouches
8. Cyclostomes like myxine, have additional chambers on the venous side of the circulation, apart from the main pumping chamber i.e. heart. They have closed circulatory system with arteries and veins.