Cyclostomata

Cyclostomata is a group of jawless vertebrates known for their long slender eel-like bodies and round sucker like mouths. They don't have jaws or paired fins and use their mouth, either attaching to other fish or for filter feeding. Common examples include Lampreys and hagfish. These animals belong to the superclass Agnatha, which includes all jawless fish. Their skeleton is made of cartilage, not bone, making them more primitive than other vertebrates. Cyclostomata is an important topic in class 11 Biology under the chapter of the animal Kingdom and often appears in exams due to unique features in classifications.

This Story also Contains

1. What are Cyclostomata?
2. Taxonomy and Classification of Cyclostomata
3. Cyclostomata Origin
4. Subdivisions of Cyclostomata
5. Cyclostomata Characteristics
6. Anatomy and Physiology of Cyclostomata
7. Cyclostomata Diagram
8. Habitat and Ecology
9. Recommended video on "Cyclostomata"

What are Cyclostomata?

The class Cyclostomata represents the jawless fish and consists of two basic divisions. These are hagfishes (Myxini) and lampreys (Petromyzontida). These animals are the absence of jaws and paired fins, which allows their study to be of major importance in understanding vertebrate evolution. Cyclostomes are among the most primitive living vertebrates, which help us to understand vertebrate development at an early stage.

Taxonomy and Classification of Cyclostomata

The taxonomy and classification of cyclostomata are described below-

Cyclostomata Origin

Below are a few points on the origin of Cyclostomata:

• They are ancient vertebrates that appeared 500 million years ago during the early Palaeozoic era.
• They evolved from early vertebrate ancestors and represent one of the most primitive forms of living vertebrates.
• Cyclostomes are part of the Agnatha superclass, which means jawless fish, and they existed even before jawed fish evolved.
• Their skeleton is made of cartilage, and a simple body structure suggests that they branched off early from the early vertebrate line.
• Fossil records of ancient jaws fish help scientists trace the evolution of the vertebral column, nervous system, backbone, and brain.

Subdivisions of Cyclostomata

The cyclostomes are subdivided into two major orders.

Myxini (Hagfishes)

• Hagfishes are soft-bodied, jawless animals that produce large amounts of slimy mucus when disturbed, which helps them escape predators.

• They are scavengers, meaning they feed on the bodies of the dead or dying animals by burrowing into them and eating from the inside.

• Hagfishes live mainly in the marine environment and are rarely seen because they stay deep in the ocean.

• Examples- Paramyxine and Myxine

Petromyzontida (Lampreys)

• Petromyzon are parasitic, meaning attach themselves to other living fish using their sucker like mountains and feed on their blood.

• They have a tooth-like mouth to latch onto their host.

• Lampreys are found in both freshwater and marine habitats, and some species even migrate between the two.

• Examples- Lampetra and Petromyzon

Also Read

• Animal Kingdom

• Phylum Mollusca

• Mammalia

Cyclostomata Characteristics

Some general characteristics of Cyclostomata are discussed below:

• Body Structure: The cyclostomes are characterised by their elongated bodies, eel-like in shape, with no paired fins, and no jaws. The mouth is sucker-like and circular.

• Skeleton: They have cartilaginous skeletons, that is, they are made of cartilage rather than bone. In addition to this, they do not have true vertebrae, only a notochord. The notochord is a long, flexible, rod-like structure that tends to help support the animal.

• Sensory Organs: The cyclostomes have rather poorly developed eyes and a lateral line system that detects vibrations and movements in the water. This enables one to steer through the medium of water and to search for food.

• Respiration: The cyclostomes breathe through gills, which are present in pairs of gill slits located on the sides of the head. These gills are used for aquatic respiration and are covered by a soft skin-like structure instead of hard gill covers.

• Circulatory system: They have a closed circulatory system with a two-chambered heart. Blood flows in one direction, unlike higher vertebrates. The red blood cells are usually nucleated. The circulation is simple but efficient for their body's needs.

• Nervous System: Cyclostomes have a simple but well-developed nervous system with a brain and a spinal cord. Their sense organs are adapted to their aquatic and parasitic life cycle, including a single median nostril and eyes that may be poorly developed in some species.

• Reproduction: Cyclostomes are unisexual, meaning, male and female reproductive parts are separate. Fertilisation is external, and they do not have larval care. The reproductive cycle involves migration to freshwater for spawning, after which the adult usually dies.

Anatomy and Physiology of Cyclostomata

The general anatomy and physiology of Cyclostomata are discussed below:

• Mouth: Circular, sucker-like structure with keratinised teeth (particularly in lampreys).

• Gill Slits: Multiple external openings along the sides of the body used for respiration.

• Nostril: Single median nostril located on the top of the head, used for olfaction.

• Eyes: Simple, lacking the complexity of higher vertebrates.

• Fins (if present): Some species may have caudal fins for stabilisation during swimming.

• Segmented Body: Cyclostomes have elongated, cylindrical bodies that are segmented.

• Setae are absent in cyclostomes, differentiating them from other segmented animals like annelids.

• Clitellum: Not present in cyclostomes, unlike in annelids such as earthworms.

Cyclostomata Diagram

The diagram below shows the different body parts of a cyclostome.

Habitat and Ecology

These cyclostomes inhabit a variety of habitats. Hagfishes are mostly deep-sea marine, while lampreys are found in both marine and freshwater systems. Lampreys also make very long migrations from one habitat to the other.

Ecological Roles:

• Some of the species, like the hagfish, act as scavengers, devouring dead and decaying remains.

• The impact that lampreys, particularly their parasitic forms, have on fish populations involves sucking their blood and feeding on tissues.

• Lampreys can significantly affect fish populations, both through predation and parasitism.

Other useful resources:

Recommended video on "Cyclostomata"