What are chondrichthyans?

Chondrichthyans , or class Chondrichthyes, are cartilaginous fishes including sharks , skates , rays , and chimaeras . They are one of the two major groups of living fishes, the other being bony fishes (Osteichthyes). They possess unique structural, physiological, biochemical, and behavioral traits, making them interesting to scientists. Many present-day sharks and rays belong to the same genera as those that lived in the Cretaceous seas over 100 million years ago, making them living fossils.

What kinds of fish are included in the chondrichthyan class?

Chondrichthyes is a class of cartilaginous fish that includes sharks , skates , rays , and chimaeras . They are one of the two main groups of living fishes, the other being the bony fishes. Chondrichthyes have skeletons made of cartilage. They have many unique structural, physiological, biochemical, and behavioral traits. Sharks, rays, and chimaerids are mostly marine, but some sharks live in fresh water. There are over 400 species of sharks and 500 species of rays.

How are chondrichthyan fish different from bony fish?

Chondrichthyes, or cartilaginous fishes , include sharks, skates, rays, and chimaeras. Osteichthyes, or bony fishes , represent the vast majority of fish species. Key distinctions: * Skeleton Bony fish have skeletons primarily of bone, while cartilaginous fish have skeletons made of cartilage. * Swim Bladder Most bony fish possess a swim bladder that helps with buoyancy, whereas cartilaginous fish lack this organ. * Scales Cartilaginous fishes have placoid scales , which are bony, spiny projections with an enamel-like covering, while bony fishes have cycloid or ctenoid scales. * Fertilization Bony fishes typically have external fertilization, while cartilaginous fishes have internal fertilization.

What is the skeleton of a chondrichthyan fish made of?

The skeleton of a chondrichthyan fish, a class that includes sharks, rays, and chimaeras, is primarily made of cartilage . Although this cartilage can be calcified, especially in the vertebrae, it lacks true bone, except in the roots of the teeth. Cartilage provides tensile strength and flexibility, crucial for bearing weight.

What are some important features of chondrichthyan skin and teeth?

Chondrichthyan, or cartilaginous fishes, including sharks and rays, possess distinguishing features in their skin and teeth. Skin Their skin is notably tough, covered in placoid scales, also known as dermal denticles. These scales are structurally similar to teeth, featuring a spiny, tooth-like shape. Each scale consists of a hollow cone of dentine surrounding a pulp cavity and is covered by a hard, enamel-like substance. Unlike bony fish, chondrichthyan scales do not grow; instead, new scales develop as the body expands. Teeth Chondrichthyan teeth are structurally modified scales. These teeth aren't firmly attached to the jaws but are embedded in a fibrous membrane. As teeth break or wear down, they are replaced by new ones from the rows behind.

How do chondrichthyans reproduce and care for their young?

Chondrichthyans, including sharks, rays, and chimaeras, exhibit diverse reproductive strategies with internal fertilization. Males use claspers, located on their pelvic fins, to transfer sperm to females. Some chondrichthyans are oviparous, laying eggs encased in a horny shell that protects the embryo as it develops. Others are ovoviviparous, where the egg hatches inside the mother, and the embryo is nourished by the yolk sac or uterine secretions. A few species are viviparous, forming a yolk-sac placenta to directly nourish the developing young. In preparation for birth, pregnant females of some shark species migrate to specific nursery areas with suitable environmental conditions. While mating behaviors have been observed in some species, they remain undocumented in others such as white sharks. After giving birth, the mother departs.

chondrichthyan

Images

southern stingray (Dasyatis americana or Hypanus americanus)

Bull shark (Carcharhinus leucas) swimming close to the sandy ocean floor in clear blue water.

Illustration of two primitive sharklike fishes from the class Chondrichthyes: Hybodus, depicted at the top with a robust body and prominent fins, and Cladoselache, shown below with a slender body and elongated tail.

Diagram showing four types of fish scales: ctenoid scales from a bass, cycloid scales from a salmon, ganoid scales from a gar, and placoid scales from a shark, each illustrated with a close-up and the corresponding fish silhouette.

Diagram of the tree of life based on the three-domain system, showing Archaea, Bacteria, and Eukaryota branching into four kingdoms: Plants, Animals, Fungi, and Protista, with illustrations of representative organisms for each group.

chondrichthyan

fish class

Also known as: Chondrichthyes, Selachii, cartilaginous fish, chondrichthian(Show More)

Written by

Lionel A. WalfordAll

Fact-checked by

Britannica Editors

Last updated

Oct. 26, 2026 •History

Top Questions

What are chondrichthyans?
Chondrichthyans, or class Chondrichthyes, are cartilaginous fishes including sharks, skates, rays, and chimaeras. They are one of the two major groups of living fishes, the other being bony fishes (Osteichthyes).

They possess unique structural, physiological, biochemical, and behavioral traits, making them interesting to scientists. Many present-day sharks and rays belong to the same genera as those that lived in the Cretaceous seas over 100 million years ago, making them living fossils.
2 Britannica Sources
1. list of sharks, skates, and rays
2. chondrichthyan: Evolution
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What kinds of fish are included in the chondrichthyan class?
Chondrichthyes is a class of cartilaginous fish that includes sharks, skates, rays, and chimaeras. They are one of the two main groups of living fishes, the other being the bony fishes.

Chondrichthyes have skeletons made of cartilage. They have many unique structural, physiological, biochemical, and behavioral traits. Sharks, rays, and chimaerids are mostly marine, but some sharks live in fresh water. There are over 400 species of sharks and 500 species of rays.
7 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How are chondrichthyan fish different from bony fish?
Chondrichthyes, or cartilaginous fishes, include sharks, skates, rays, and chimaeras. Osteichthyes, or bony fishes, represent the vast majority of fish species.

Key distinctions:
* Skeleton Bony fish have skeletons primarily of bone, while cartilaginous fish have skeletons made of cartilage.
* Swim Bladder Most bony fish possess a swim bladder that helps with buoyancy, whereas cartilaginous fish lack this organ.
* Scales Cartilaginous fishes have placoid scales, which are bony, spiny projections with an enamel-like covering, while bony fishes have cycloid or ctenoid scales.
* Fertilization Bony fishes typically have external fertilization, while cartilaginous fishes have internal fertilization.
10 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What is the skeleton of a chondrichthyan fish made of?
The skeleton of a chondrichthyan fish, a class that includes sharks, rays, and chimaeras, is primarily made of cartilage. Although this cartilage can be calcified, especially in the vertebrae, it lacks true bone, except in the roots of the teeth. Cartilage provides tensile strength and flexibility, crucial for bearing weight.
8 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What are some important features of chondrichthyan skin and teeth?
Chondrichthyan, or cartilaginous fishes, including sharks and rays, possess distinguishing features in their skin and teeth.

Skin

Their skin is notably tough, covered in placoid scales, also known as dermal denticles. These scales are structurally similar to teeth, featuring a spiny, tooth-like shape. Each scale consists of a hollow cone of dentine surrounding a pulp cavity and is covered by a hard, enamel-like substance. Unlike bony fish, chondrichthyan scales do not grow; instead, new scales develop as the body expands.

Teeth

Chondrichthyan teeth are structurally modified scales. These teeth aren't firmly attached to the jaws but are embedded in a fibrous membrane. As teeth break or wear down, they are replaced by new ones from the rows behind.
3 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How do chondrichthyans reproduce and care for their young?
Chondrichthyans, including sharks, rays, and chimaeras, exhibit diverse reproductive strategies with internal fertilization. Males use claspers, located on their pelvic fins, to transfer sperm to females.

Some chondrichthyans are oviparous, laying eggs encased in a horny shell that protects the embryo as it develops. Others are ovoviviparous, where the egg hatches inside the mother, and the embryo is nourished by the yolk sac or uterine secretions. A few species are viviparous, forming a yolk-sac placenta to directly nourish the developing young.

In preparation for birth, pregnant females of some shark species migrate to specific nursery areas with suitable environmental conditions. While mating behaviors have been observed in some species, they remain undocumented in others such as white sharks. After giving birth, the mother departs.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

chondrichthyan, (class Chondrichthyes), any member of the diverse group of cartilaginous fishes that includes the sharks, skates, rays, and chimaeras. The class is one of the two great groups of living fishes, the other being the osteichthians, or bony fishes. The name Selachii is also sometimes used for the group containing the sharks.

Many unique structural, physiological, biochemical, and behavioral characters make these fishes of particular interest to scientists. The dissection of a small shark is often the biology student’s introduction to vertebrate anatomy. These fishes are, in a sense, living fossils, for many of the living sharks and rays are assigned to the same genera as species that swam the Cretaceous seas over 100 million years ago. More than 400 species of sharks and about 500 species of rays are known. Although by any reckoning a successful group, the modern chondrichthyans number far fewer species than the more advanced bony fishes, or teleosts.

The danger some sharks and stingrays present to humans makes these animals fascinating and, at the same time, fearsome. Perhaps for this reason, they figure prominently in the folklore and art of many tropical peoples who depend on the sea. The danger from shark attack, while very real, is remarkably uncommon and easily sensationalized. Quite frequently, little attempt is made to distinguish between dangerous and harmless species.

General features

Problems of taxonomy

The name Selachii refers to a category of fishlike vertebrates characterized by a skeleton primarily composed of cartilage. Selachii are given a variety of treatments by ichthyologists. Some authorities consider Selachii to be a class or subclass that contains all the modern sharks and rays; other authorities restrict the use of the name to an order of modern sharks and certain extinct ancestral forms. Under the latter system, the rays (including the sawfishes, guitarfishes, electric rays, mantas, skates, and stingrays) are ranked separately.

Young chimpanzee dressed in a shirt and sweater vest, scratching his head thinking. (primates)

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The chimaeras (Holocephali) bear many similarities to sharks and rays in skeletal structure, internal organs, and physiology. Ichthyologists commonly although not unanimously emphasize these similarities by grouping the modern and ancient sharks, rays, and chimaeras in the class Chondrichthyes, the cartilaginous fishes. Under this system, which is used in the present article, the sharks, skates, and rays are further grouped into one subclass, Elasmobranchii, and the chimaeras into another, Holocephali. Some authorities classify the elasmobranchs into one class (Selachii) and classify the chimaeras into another (Holocephali); however, assigning the two groups class rank implies a degree of distinctness equal to that of the amphibians (Amphibia), reptiles (Reptilia), birds (Aves), and mammals (Mammalia).

Distribution and abundance

The majority of sharks and rays are marine fishes, but many enter estuaries; some travel far up rivers, and a few are permanent residents of fresh water. Most species live in the relatively shallow waters of continental margins or around offshore islands; a few roam far out in the vast spaces of the oceans. Some live at great depths, in midwaters or on the bottom; others are surface swimmers or inhabit the bottom in shallow waters.

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Once regarded as “trash” fish, sharks and rays are increasingly represented in the fisheries of most countries. With numbers of more highly valued bony fishes decreasingly rapidly, many fisheries are specifically targeting elasmobranchs as a primary commercial resource. Annual yields are as much as 750,000 metric tons (roughly 827,000 short tons), and most of this is sold fresh, dried, salted, or processed. This intense harvest is causing the reduction of many shark and ray populations and, in some cases, causing the commercial extinction of some species. One consequence of this depletion of these top-level predators may be a disruption of the food chain in marine ecosystems.