Chondrichthyes - Definition, Classification, Characteristics, Examples & Facts

Chondrichthyes - Cartilaginous Fish

Chondrichthyes are a class of cartilaginous fish under Phylum Chordata and Subphylum Vertebrata. They are called cartilaginous fish because their skeleton is made of cartilage tissue, not bone. They have placoid scales, a ventral mouth and 5-7 pairs of gill slits without an operculum. Cartilaginous fishes' buoyancy is maintained by oil- rich liver instead of swim bladders.

These fish are known worldwide by many names: peixes cartilaginosos (Portuguese), condroitti (Italian), knorpelfisch / knorpelfische (German), paryby / paryba (Czech, Polish), peces cartilaginosos / condrictios / condrictes (Spanish, Catalan), pesci cartilaginei (Italian), and broskfisk (Swedish). All these terms mean the same group of fish with cartilage skeletons.

Examples include sharks (Scoliodon, Rhincodon), rays (Torpedo, Trygon), sawfishes (Pristis), and chimaeras (Ghost shark). As top predators, they regulate prey populations and maintain marine ecosystem balance.

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.

Chodrichthyes 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.

Characteristics of Cartilaginous Fish

Chondrichthyes are cartilaginous fishes. Their skeleton is composed of cartilage instead of bone, providing flexibility and durability. Some of the characteristics of chondrichthyes fish are -

• Placoid scales: These are the tooth-like overlapping scales that help reduce drag. Hence, it improves swimming efficiency.

• Fins: Cartilaginous fishes have different fin shapes that allow for stability and survival.

• No swim bladder: The cartilaginous fishes' buoyancy is maintained by large livers filled with oil.

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

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

• Osmoregulation: It is the ability to maintain constant internal salt concentrations in various marine environments.

Unique Characteristics of Chondrichthyes in tabular form:

Reproduction in Chondrichthytes

Reproduction in cartilaginous fish is unique among vertebrates. These cartilaginous fishes show internal fertilisation using claspers. Depending on the species. They may be -

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.

This diversity in reproductive modes of cartilaginous fish helps them to adapt to the marine ecosystem and ensure the survival of their offspring.

Examples of Cartilaginous Fish

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: The protection of chondrichthyes fishes comes from the sustainable fishing methods and protecting marine areas as part of conservation efforts. These are affected by overfishing, bycatch, habitat loss, and pollution.

• Human-shark interaction: The shark behaviour pattern can help minimise the conflicts in such a way that safety is well-balanced with their conservation.

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

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 the teeth are modified, placoid scales directed backwardly. The air bladder is absent. Eg, Torpedo, Scoliodon, Pristis, Petromyzon. All Chondrichthyes possess cartilaginous exoskeletons without 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.

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