Table of Contents

Kingdom Animalia – Agnatha and Pieces

In the previous segment of the chapter ‘Diversity in Living Organisms’, we studied about the

Chordates. In this segment, let us get introduced to Agnatha and Pieces.

What is Agnatha?

Agnatha, also called Cyclostomata, is a superclass of vertebrates which include the primitive jawless fishes.

For example, hagfish, lamprey, etc.

They have a round mouth with rings of cartilage. These rings have saw-like structures arranged in rows that act as teeth.
They have a skull or cranium but a proper spinal cord is absent.
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 smooth.
There are tiny pores on the sides used for breathing.

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 meal.
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 together.
The fertilisation in these organisms is external. The lamprey larvae are extremely tiny and mostly live in freshwater or muddy water.

What is the typical body structure of a fish?

Body structure of Pisces