The animals that belong to the class Pisces are commonly known as fishes. It belongs to the phylum Chordata. They have two sets of paired fins known as pectoral and pelvic fins, and in the middle line, it is comprised of dorsal, anal, and caudal fins.
The class Pisces is further into two subclasses, they are Chondrichthyes and Osteichthyes:
Chondrichthyes: Commonly referred to as cartilaginous fishes.
Osteichthyes: Commonly referred to as bony fishes.
Let us learn more about subclasses of the Pisces.
Chondrichthyes in the Greek language has the following meaning, chondr means ‘Cartilage’ and ichthyes means ‘Fish’. The class Chondrichthyes means a class that contains cartilaginous fishes whose skeleton is composed of cartilage.
Chondrichthyes is further subdivided into two subclasses:
In Greek, elasmo means ‘Plate’ and branchia means ‘gill’, hence we can tell that long and broad flattened gills are the characteristics of these fishes. It includes sharks and rays, skates, and sawfishes.
The word Holocephali means ‘complete head’. It includes Chimaeras, also known as ghost sharks.
The classification of Chondrichthyes is as follows:
Some of the Chondrichthyes examples are:
Sharks: Dogfish, Whale shark, Angel shark, Ground Shark, etc.
Rays: Electric ray, String ray, Manta ray, etc.
Skates: Little skate, Small deepwater skate, Andaman leg skate, etc.
Sawfishes: Narrow sawfish, Dwarf sawfish.
The cartilaginous fish characteristics are as follows:
Chondrichthyes are marine fishes that contain powerful jaws.
The second-largest vertebra and the largest fish, whale sharks belong to this class and it can be measured to a length of 15m.
The mouth is present on the ventral side.
The endoskeleton is made up of cartilage and the calcium deposits provide strength to it.
The presence of notochord can be throughout life.
The tail contains two lobes, the elongated upper lobe, and the shorter lower lobe. The vertebrae can be extended into the upper lobe and the distinct heterocercal tail arises from the lower lobe.
The skin is covered with placoid scales.
They have five to seven pairs of gills.
They have to swim continuously to avoid sinking as they lack air bladders.
They cannot regulate their internal body temperature as they are poikilothermic animals.
They feed on the other fishes, mollusks and the crustaceans hence called predatory fishes.
They have 2 chambered hearts which consist of one auricle and one ventricle.
They have a brain and spinal cord that is protected by the vertebral column.
Chondrichthyes sharks contain special sense organs called electroreceptors on their head which help them to detect their prey which also helps in navigation.
They have poison sting which provides protection from the enemies and also helps in the predation.
Chondrichthyes digestive system: The digestive system consists of the mouth, pharynx, stomach, intestine, and cloaca. In females, the cloaca has a dual function it can be used as a reproductive organ and as an excretory organ.
The fertilization is internal. Some of them are oviparous and some of them are viviparous.
These are the major Chondrichthyes characteristics some of these might be characteristics of the Osteichthyes.
The general characteristics of Chondrichthyes and Osteichthyes are as follows:
They belong to the same phylum Pisces.
They both have endoskeleton and exoskeleton.
They can breathe through gills.
They have jaws and paired appendages.
They can be oviparous, viviparous, or oviviviparous.
The phylum Pisces has two different classes which are divided based on the composition of the endoskeleton and they are Chondrichthyes and Osteichthyes. These are found in both marine and freshwater. The fishes are not only important to balance the ecosystem but also very important to human beings because they provide nutrients and micronutrients which plays an important role in the diet as it controls most of the diseases. These nutrients are essential for the physical development of children. They are an important source of income and employment for the people living in coastal regions of many developing countries.
1. Write the difference between Chondrichthyes and Osteichthyes.
Smaller in size compared to Chondrichthyes
Position of mouth
Placoid scales are present
Cycloid scales are present
Number of gills
Five to seven pairs of gills are present excluding the operculum.
Four pairs of gills are present including the operculum.
Has a single set of jaws
Two sets of jaws are found.
2. Why do Sharks consider Cartilaginous Fishes?
Sharks, skates, and rays all of these fishes have cartilaginous Skeleton because the density of the cartilage is very less which helps the sharks to move faster in the water without the use of more energy and keeps them afloat. As the density of the cartilage is less as compared to the bones it provides more flexibility and hence they can bend easily as compared to the bony fishes.
3. Write down the characteristics of Cartilaginous Fish.
The characteristics of cartilaginous fish are as follows:
The endoskeleton is made up of cartilage.
They have paired gills and fins.
The heart is two-chambered.
The body is covered by placoid scales.
The fertilization takes place internally.
They lack a swim bladder.