Chondrichthyes - Definition, Classification, Characteristics, Examples & Facts

Chondrichthyes Classification

Chondrichthyes are a class of vertebrates known as cartilaginous fishes. The notochord is present throughout life, and the skeleton remains cartilaginous instead of forming a bony vertebral column (osteichthyes). This unique trait separates cartilaginous fishes from other vertebrates. The classification of Chondrichthyes highlights their evolutionary link to the Animal Kingdom, Phylum Chordata, Subphylum Vertebrata, and Superclass Pisces.

Chondrichthyes are divided into these subclasses:

1. Elasmobranchii (sharks, rays, and skates)

• It has predatory and streamlined bodies with skeletons made of cartilage, many rows of teeth, and electroreceptive organs.

• Examples: Great White Shark, Manta Ray.

2. Holocephali (chimaeras)

• Unique, rabbit-like faces with specialised dental plates; single gill opening.

• Examples: Ratfish, Ghost Shark.

Also Read:

• Cephalochordata

• Amphibia

• Phylum Platyhelminthes

Chondrichthyes Characteristics

Chondrichthyes are cartilaginous fishes. Their skeleton is composed of cartilage instead of bone, providing flexibility and durability.

• Placoid scales: The tooth-like overlapping scales help reduce drag, hence improving swimming efficiency.

• Fins: It has different fin shapes that allow for stability and survival.

• No swim bladder: Buoyancy is maintained by large livers filled with oil.

• Respiration: Efficient oxygen extraction from water is possible through the gill slits, while some species have spiracles, which are respiratory organs usually used while resting on the ocean floor.

• Control of buoyancy: The liver stores oil changes to maintain buoyancy.

• Osmoregulation: Ability to maintain constant internal salt concentrations in various marine environments.

Reproduction in Chondrichthytes

1. Oviparous: The eggs are laid outside and develop outside the female's body, e.g., skates.

2. Ovoviviparous: The eggs hatch inside the female body and are born live. Example: Most sharks.

3. Viviparous: Embryos develop inside the female. They get nourishment directly from the mother. Example: Some sharks.

Chondrichthyes Examples

The prominent examples of cartilaginous fishes are:

Rays

• Torpedo (Electric ray)

• Narcine bancroftii (Lesser electric ray)

• Trygon (Stingray)

• Manta (Manta ray)

Sharks

• Rhincodon (Whale shark)

• Scoliodon (Dogfish)

• Charcarodon charcharias (The great white shark)

Sawfishes

• Anoxypristis cuspidata (Narrow sawfish)

• Pristis clavata (Dwarf sawfish)

Skates

• Cruriraja andamanica (Andaman leg skate)

• Leucoraja erinacea (Little skate)

• Gurgesiella (Small deepwater skate)

Chimaeras

• Callorhinchus milii (Australian ghost shark)

• Hydrolagus alphus (Whitespot ghost shark)

• Chimaera argiloba (Whitefin chimaera)

Ecological Importance of Chondrichthyes

Chondrichthyes are top predators in regulating prey populations. They maintain ecological balances, and their effects eventually lead to biodiversity and the stability of ecosystems.

• Conservation: Protection of chondrichthyes fishes comes with sustainable fishing methods and protected marine areas as part of conservation efforts.

• They are also challenged by overfishing, bycatch, habitat loss, and pollution.

• Chondrichthyes are economically relevant through fisheries and, more recently, by ecotourism activities such as shark diving.

• Human-shark interaction: Understanding shark behaviour minimises conflicts in such a way that safety is well-balanced against conservation.

Chondrichthyes NEET MCQs (With Answers & Explanations)

Question 1: Which one of the following groups of animals is correctly matched with its one characteristics feature without even a single exception?

1. Reptilia: possess a 3-chambered heart with one incompletely divided ventricle

2. Chordata: possess a mouth provided with an upper and lower jaw

3. Chondrichthyes: possess a cartilaginous endoskeleton

4. Mammalia: give birth to young ones.

Correct Answer: 3) Chondrichthyes: possess a cartilaginous endoskeleton

Explanation:

Marine and predatory. The mouth is located ventrally and teeth are modified, placoid scales directed backwardly. The air bladder is absent. Eg, Torpedo, Scoliodon, Pristis, Petromyzon. All Chondrichthyes possess cartilaginous exoskeletons without any exception. Their mouth is located ventrally, and their teeth are modified for capturing prey, often appearing in multiple rows. These fish are covered with placoid scales that are directed backwards, providing a rough texture to their skin. Notably, they lack an air bladder, which affects buoyancy, as they rely on their large liver for this purpose. Examples of Chondrichthyes include Torpedo, Scoliodon, Pristis, and Petromyzon, all of which possess cartilaginous exoskeletons without exception.

Hence, the correct answer is option 3) Chondrichthyes: possess a cartilaginous endoskeleton

Question 2: A marine cartilaginous fish that can produce an electric current is:

1. Pristis

2. Torpedo

3. Trygon

4. Scoliodon

Correct Answer: 2) Torpedo

Explanation:

Torpedo is a marine cartilaginous fish that produces 8-220 volt electric charge (current) depending on species. Their electric organs are modified lateral muscle plates innervated by cranial nerves. Trygon (sting ray) resembles an electric ray in many aspects but is devoid of electricity-discharging (or producing) organs. Scoliodon (dogfish) is known for its great sense of smell. Pristis or common sawfish (also known as carpenter shark) is characterised by a long, narrow, flattened rostrum lined with sharp transverse teeth to resemble a saw.

Hence, the correct answer is option 2) Torpedo.

Question 3: Chondrichthyes is characterised by

1. Placoid scale

2. Ventral mouth

3. Ctenoid scale and ventral mouth

4. Placoid scale and ventral mouth

Correct Answer: 4) Placoid scale and ventral mouth

Explanation:

Chondrichthyes, or cartilaginous fish, such as sharks, rays, and skates, are distinguished by their placoid scales. The fish can glide more smoothly through the water thanks to these tiny, tooth-like scales that lower friction. The mouth of chondrichthyes is usually ventral, which means it is situated on the underside of the body. The reason the other choices are wrong is the ctenoid scale: Unlike cartilaginous fish, ctenoid scales are seen in bony fish (Osteichthyes). Ventral mouth with Ctenoid scale: This choice is untrue because Chondrichthyes do not have Ctenoid scales.

Hence, the correct answer is option 4)Placoid scale and ventral mouth.

Other useful resources:

• Difference Between Chordates and Non-chordates

• Mammalia

• Urochordata

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