Super Class - Pisces (Chondrichthyes & Osteichthyes) | Biology for JAMB PDF Download

Pisces

• Pisces are aquatic vertebrates with gills for respiration and lack a true spine.
• They inhabit fresh, marine, and brackish water environments.
• Fins are the organs of locomotion, which can be paired or unpaired.
• The study of fishes is known as ichthyology.
• It is believed that they evolved from sea-squirts, resembling primitive fish.

Pisces

Classification of Pisces:

• Pisces belong to the Kingdom Animalia, Phylum Chordata, Super-class Gnathostomata, and Class Pisces.

Characteristics of Pisces:

• Pisces have a streamlined body with a close circulatory system.
• The body is divided into head, trunk, and tail regions.
• The skeleton can be bony or cartilaginous.
• They exhibit separate sexes and possess a well-developed digestive system.
• Fertilization can be internal or external, and they have scales for external covering.
• They can display herbivorous, carnivorous, or omnivorous feeding habits.

Further Classification of Pisces

Placodermi:

• Extinct class of fishes, known through fossils.
• First fishes with jaws, survived until the Permian period of the Paleozoic era.
• Characterized by bony endoskeleton and heterocercal caudal fin.
• Includes orders like Arthrodiriformes and Antiarchiformes.

Chondrichthyes:

• Also known as elasmobranch, found only in marine waters.
• Features absence of operculum, cartilaginous endoskeleton, and heterocercal caudal fin.
• Subclasses include Selachi and Bradyodonti.

Osteichthyes:

• Largest class of vertebrates with bony internal skeletons.
• Divided into subclasses like Dipnoi, Crossopterygii, and Actinopterygii.
• Presence of autostylic jaw suspension and air bladder in this class.

Physiological Aspects of Pisces

Respiration:

• Fishes respire through gills, with oxygen uptake and carbon dioxide release.
• Gill structures vary among species, with some possessing lungs for respiration.

Excretion:

• Main excretion in fishes is urea, with gills also serving as excretory organs.
• Special adaptations may be present in freshwater species for water excretion.

Circulation:

• Fish have a closed circulatory system with a two-chambered heart.
• Blood flow involves oxygenation in the gills before distribution throughout the body.

Reproduction:

• Fish reproductive organs are internal, with external fertilization being common.
• Examples include scattering eggs in water for fertilization and internal hatching in some species.

Neurological and Sensory Features of Pisces

Nervous System:

• The nervous system comprises the central nervous system (CNS) and peripheral nervous system (PNS).
• Control and coordination during swimming are key functions of the nervous system.

Sensory Organs:

• Fish possess specialized sensory organs for vision, hearing, and reproduction.
• Examples include eyes adapted for underwater vision and internal reproductive structures.