Medicneet Logo

Class Chondrichthyes: Cartilaginous Fishes (Sharks and Rays)

Biology · Animal Kingdom · NEET

Chondrichthyes are the cartilaginous fishes, like sharks and rays. Their whole skeleton is made of cartilage (soft, flexible bone), not hard bone. They live in the sea, have a mouth on the underside (ventral), and have NO air bladder, so they must keep swimming or they sink. Memory hook: "Chondro" = cartilage, so Chondrichthyes = cartilage-fish that never stops swimming.
Class Chondrichthyes: Key Features (Shark)Mouth ventralGill slits (no operculum)Heterocercal finCartilage skeleton, Placoid scales, NO air bladder (must keep swimming)Marine, Notochord persistent, Poikilothermous, Internal fertilisation, often viviparous
A shark showing the diagnostic features of Chondrichthyes: ventral mouth, separate gill slits without an operculum, unequal (heterocercal) tail fin, cartilaginous skeleton, placoid scales, and no air bladder.

Your doubts, answered

Is the skeleton of Chondrichthyes made of cartilage or bone?

It is made ONLY of cartilage. Cartilage is a soft, flexible tissue (like the tip of your nose or ear). This is the single most tested fact: 'cartilaginous endoskeleton always holds true for Chondrichthyes.' There is no true bone anywhere in their body. This is why the class is named Chondrichthyes ('chondro' means cartilage).

Why do sharks have to keep swimming all the time?

Because they have NO air bladder. In bony fishes (Osteichthyes), the air bladder is a gas-filled sac that helps them float and stay at one depth without effort. Chondrichthyes lack this sac, so they are heavier than water and would sink. To avoid sinking, they must swim constantly. This 'no air bladder = constant swimming' link is a common NEET question.

Do Chondrichthyes have an operculum (gill cover)?

No. Their gill slits are separate and open directly to the outside, WITHOUT an operculum covering them. Sharks show 5-7 open gill slits on the side. Only bony fishes (Osteichthyes) have an operculum. NEET uses this to catch you: 'all pisces have gills covered by an operculum' is FALSE, because Chondrichthyes have no operculum.

What are placoid scales?

Placoid scales are tiny, tough, tooth-like scales that cover the skin of Chondrichthyes. They make shark skin rough like sandpaper. Important twist: the teeth of these fishes are actually MODIFIED placoid scales that point backward. So the 'teeth' and 'skin scales' are the same kind of structure.

Is the notochord present in Chondrichthyes?

Yes. The notochord is PERSISTENT throughout life in Chondrichthyes (it does not fully disappear in the adult). Per NCERT this statement is TRUE. Do not confuse it with higher vertebrates, where the notochord is replaced by the vertebral column. NEET 2026 tested this exact statement.

What is the difference between Chondrichthyes and Osteichthyes?

Chondrichthyes = cartilage skeleton, no air bladder, no operculum, placoid scales, ventral mouth, always marine, must swim to not sink (sharks, rays). Osteichthyes = bony skeleton, has air bladder, has operculum, cycloid/ctenoid scales, terminal mouth, marine or freshwater (Exocoetus, Pterophyllum, Betta). This pair is one of the most tested contrasts in the chapter.

Are Chondrichthyes cold-blooded or warm-blooded, and how do they reproduce?

They are poikilothermous (cold-blooded), meaning their body temperature changes with the water. Sexes are separate. Fertilisation is internal, and many of them are viviparous (give birth to young ones). In males, the pelvic fins bear claspers used during mating.

⚠️ The NEET trap
✗ All fishes (pisces) have their gills covered by an operculum.
✓ Only Osteichthyes have an operculum. Chondrichthyes have separate gill slits with NO operculum, so this statement is false.
🧠 Operculum = 'Osteichthyes only'. Both start with O. Sharks show open gill slits, no cover.

Real NEET questions

NEET 2016 Phase 1

Which of the following characteristic features always holds true for the corresponding group of animals?

A · Cartilaginous endoskeleton - Chondrichthyes ✓
B · Viviparous - Mammalia
C · Possess a mouth with an upper and a lower jaw - Chordata
D · 3-chambered heart with one incompletely divided ventricle - Reptilia
Solution: A cartilaginous endoskeleton ALWAYS holds true for Chondrichthyes, so (a) is correct. (b) fails because egg-laying mammals (Ornithorhynchus, Echidna) exist and are not viviparous. (c) fails because jawless cyclostome chordates have no jaws. (d) fails because crocodiles are reptiles with a four-chambered heart.
NEET 2016 Phase 2

Choose the correct statement.

A · All mammals are viviparous
B · All cyclostomes do not possess jaws and paired fins ✓
C · All reptiles have a three-chambered heart
D · All pisces have gills covered by an operculum
Solution: (b) is correct: cyclostomes are jawless and lack paired fins. (d) is the Chondrichthyes trap: it is FALSE because Chondrichthyes (sharks, rays) have separate gill slits with NO operculum, so not all pisces have a gill cover. (a) fails due to egg-laying mammals; (c) fails because crocodiles have a four-chambered heart.
NEET 2020

Match the columns: (a) 6-15 pairs of gill slits (b) Heterocercal caudal fin (c) Air bladder (d) Poison sting with (i) Trygon (ii) Cyclostomes (iii) Chondrichthyes (iv) Osteichthyes

A · a-iv, b-ii, c-iii, d-i
B · a-i, b-iv, c-iii, d-ii
C · a-ii, b-iii, c-iv, d-i ✓
D · a-iii, b-iv, c-i, d-ii
Solution: 6-15 pairs of gill slits = Cyclostomes, so a-ii. The heterocercal (unequal-lobed) caudal fin is a feature of cartilaginous fishes, so b-iii (Chondrichthyes). The air bladder for buoyancy is only in bony fishes, so c-iv (Osteichthyes). The poison sting is borne by Trygon, so d-i. Correct match is option C.

Solved Animal Kingdom NEET PYQs

Try the real previous-year questions from this chapter — each with the answer and a full solution.

See all 41 Animal Kingdom NEET PYQs ›
Next concept: Class Osteichthyes →Keep learning — 2 minFeeling ready? Solve the Animal Kingdom NEET PYQs ›Or practice on your phone — get the free MedicNEET app ›

Frequently asked

Give NCERT examples of Chondrichthyes.

Scoliodon (Dog fish), Pristis (Saw fish), Carcharodon (Great white shark), Trygon (Sting ray), and Torpedo (Electric ray). Trygon is famous for its poison sting.

Where is the mouth located in Chondrichthyes?

The mouth is located ventrally (on the lower/under side of the head). In bony fishes the mouth is usually terminal (at the front tip).

Are Chondrichthyes marine or freshwater?

They are marine (sea-living) animals with a streamlined body. This is a fixed NCERT fact for the class.

What kind of scales and teeth do they have?

They have minute placoid scales in the tough skin. Their teeth are modified placoid scales that point backward, and their jaws are very powerful because they are predators.

How do Chondrichthyes reproduce?

Sexes are separate. Fertilisation is internal and many are viviparous. Males have claspers on the pelvic fins used to transfer sperm during mating.

Related concepts:
Class Osteichthyes: Bony Fishes and the Air BladderDifference Between Chondrichthyes and OsteichthyesWhat Is the Air Bladder and Why Bony Fishes Have ItClass Cyclostomata: Jawless Ectoparasitic FishesCold-Blooded vs Warm-Blooded: Poikilotherms and Homeotherms
Practise Biology for NEET:
Biology MCQs (free, chapter-wise)Animal Kingdom PYQs