elasmobranch

References

elasmobranch

fish subclass

Also known as: Elasmobranchii

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Last updated

June 26, 2026

Quick Summary

Elasmobranchs are a subclass of cartilaginous fishes that include sharks, rays, and skates. Unlike bony fishes, their skeletons are made of cartilage, though it can be calcified. They typically have five to seven gill openings on each side of their body that open separately to the exterior.123

Key characteristics include:
* Scales: Their skin is covered in tiny, tooth-like structures called dermal denticles.3
* Teeth: Teeth are not fused to the jaw but are embedded in a membrane and are continuously replaced as they are lost or worn.3
* Intestine: A spiral valve within the intestine helps increase surface area for nutrient absorption.3
* Spiracles: Many sharks and all rays have a small opening behind the eye called a spiracle, which is a modified gill cleft used for respiration.3

Elasmobranchs evolved from placoderms, an extinct group of armored fishes, during the Devonian Period, around 350 million years ago.4

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chondrichthyan
Problems of taxonomy
…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…
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…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…
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reproductive behaviour
Fishes
All cartilaginous fishes—the elasmobranches (e.g., sharks, rays, and skates)—employ internal fertilization and usually lay large, heavy-shelled eggs or give birth to live young. The most characteristic features of the more primitive bony fishes is the assemblage of polyandrous (many males) breeding aggregations in open water and the absence…
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All cartilaginous fishes—the elasmobranches (e.g., sharks, rays, and skates)—employ internal fertilization and usually lay large, heavy-shelled eggs or give birth to live young. The most characteristic features of the more primitive bony fishes is the assemblage of polyandrous (many males) breeding aggregations in open water and the absence…
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bone
Evolutionary origin and significance
…ancestors of the cyclostomes and elasmobranchs had armoured headcases, which served largely a protective function and appear to have been true bone, modern cyclostomes have only an endoskeleton, or inner skeleton, of noncalcified cartilage and elasmobranchs a skeleton of calcified cartilage. Although a rigid endoskeleton performs obvious body supportive functions…
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…ancestors of the cyclostomes and elasmobranchs had armoured headcases, which served largely a protective function and appear to have been true bone, modern cyclostomes have only an endoskeleton, or inner skeleton, of noncalcified cartilage and elasmobranchs a skeleton of calcified cartilage. Although a rigid endoskeleton performs obvious body supportive functions…
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spiracle
In elasmobranch and ganoid fishes a pair of spiracles, derived from the gills, is used as a water passageway during respiration. The nasal opening of whales and other cetaceans is called a spiracle, as is the respiratory opening behind the eyes of rays and skates. In…
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In elasmobranch and ganoid fishes a pair of spiracles, derived from the gills, is used as a water passageway during respiration. The nasal opening of whales and other cetaceans is called a spiracle, as is the respiratory opening behind the eyes of rays and skates. In…
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