Chondrichthyes - Classification, Characteristics and Reproduction

Chondrichthyes: Chondrichthyes, also known as cartilaginous fish, represent a class of jawed fish characterized by skeletons primarily composed of cartilage rather than bone. This sets them apart from osteichthyes, or bony fishes, another major group. Members of Chondrichthyes include sharks, skates, rays, and chimaeras.

Chondrichthyes Classification

Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Superclass: Gnathostomata

Class: Chondrichthyes

1. Elasmobranchii: This subclass encompasses sharks, rays, skates, and sawfish. Elasmobranchs are characterized by their entirely cartilaginous skeletons, five to seven pairs of gill slits located on their bodies' sides, and placoid scales, which give their skin a rough texture.
2. Holocephali: This subclass comprises chimaeras, also known as ghost sharks. Holocephalans possess a distinctive head structure with a single median dorsal fin and a bony plate in their upper jaw. Unlike elasmobranchs, holocephalans have four pairs of gill slits covered by an operculum (a bony flap) and cycloid scales resembling those of bony fishes.

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Chondrichthyes Characteristics

1. Cartilaginous Skeleton: Chondrichthyes have skeletons primarily composed of cartilage, a flexible connective tissue. Although some calcification may occur for reinforcement, they lack the true bones found in Osteichthyes.
2. Placoid Scales: Their skin is covered in tough, tooth-like placoid scales structurally similar to teeth. These scales reduce drag during swimming and provide protective armor.
3. Heterocercal Tail: Most Chondrichthyes possess a heterocercal tail, characterized by an asymmetrical tail fin where the upper lobe is larger than the lower lobe. This design enhances swimming efficiency and is reminiscent of sharks and some primitive bony fish.
4. Gills for Respiration: Chondrichthyes extract oxygen from water through their gills. Unlike bony fish, they lack swim bladders, relying on constant swimming to maintain buoyancy.
5. Predatory Nature: Most Chondrichthyes are carnivorous, adapted for hunting with keen senses, powerful jaws bearing multiple rows of replaceable teeth, and streamlined bodies for efficient movement. Sharks, skates, and rays are examples of Chondrichthyes.
6. Cold-Blooded : Chondrichthyes are poikilothermic, meaning their internal body temperature fluctuates with the surrounding environment, as they lack mechanisms for regulating their temperature.

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Chondrichthyes Examples

• Sharks: Among the most recognizable cartilaginous fish, sharks exhibit a wide range of sizes and shapes. From the enormous whale shark, exceeding 40 feet in length, to the diminutive dwarf pygmy shark, measuring just 6 inches long.
• Rays: Rays are flat-bodied fish that inhabit the ocean floor. They possess wing-like pectoral fins used for swimming and burrowing in the sand. Common types of rays include stingrays, manta rays, and electric rays.
• Skates: Skates resemble rays but feature more pointed snouts and triangular pectoral fins. They are typically found in shallow coastal waters worldwide.
• Chimaeras: Also referred to as ghost sharks, chimaeras are a group of deep-sea fish distinguished by a rabbit-like snout and a long, slender tail. Chimaeras are the least common type of cartilaginous fish.

Chondrichthyes Reproduction

**Oviparity**

Systole and Diastole

**Viviparity**

Sexual Reproduction in Flowering Plants

Chondrichthyes are Oviparous or Viviparous