What is Agnatha?
Hagfish
- Agnatha, also called Cyclostomata, is a superclass of vertebrates which include the primitive jawless
For example, hagfish, lamprey, etc.
Lamprey
- They have a round mouth with rings of cartilage. These rings have saw-like structures arranged in rows that act as
- They have a skull or cranium but a proper spinal cord is
- The absence of jaws is the most significant difference between these organisms and the true fishes. Another difference is their skin. They do not have scales on their body and their skin is
- There are tiny pores on the sides used for
Round mouth of Agnatha
- Hagfish secrete some slimy mucus as a part of a defence mechanism. When the hagfish is feeding on other creatures, it also secretes a lot of mucus to keep the other fishes away from attacking their
- Most of the agnatha are detritivores and rely largely on dead organisms. They have a developed digestive system but it lacks a proper stomach. The gut is more or less a uniform tube-like structure throughout. They have a slow rate of metabolism. If the temperature around the organism drops below expected, then the slow rate of metabolism enables it to stay alive without eating food for days
- The fertilisation in these organisms is The lamprey larvae are extremely tiny and mostly live in freshwater or muddy water.
What are Pieces?
- Pisces is the superclass of jawed vertebrates including
What is the typical body structure of a fish?
Body structure of Pisces
Shark – Cartilaginous skeleton
- The tapering ends and bulged centre makes the body of fishes streamlined. It helps the body to cut through the force of
- The body of fishes have a proper bony skeleton or the endoskeleton is made up of cartilage.
For example, sharks have cartilaginous skeletons while codfish, tuna, and salmon are bony fishes.
Bony fishes
- The body of most fishes is bilaterally symmetrical and triploblastic. Their body has scales and the appendages are reduced to fins that help them in
- The change in direction is aided by a single caudal fin in most of the
- Fishes have a well-developed digestive
Respiratory system of Pisces
Countercurrent mechanism in Pisces
- The respiratory system helps in taking in the dissolved oxygen from water which is very less compared to the oxygen in the
- The respiration occurs with the help of gills present internally on either side. Water is taken in through the mouth and given out through the gills. The counter-current mechanism helps in taking in the dissolved oxygen from the
Nervous system of Pisces
- Fishes possess a well-developed brain. Most of their senses and systems are coordinated by their brain located in the head
- The circulatory system is also developed. Fishes have a two-chambered heart. Blood vessels run throughout their
- Sexes in fishes are separate. Fertilisation can be both internal as well as external depending upon the
