claspers. They have internal fertilisation and many of them are viviparous. Examples: Scoliodon (Dog fish), Pristis (Saw fish), Carcharodon (Great white shark), Trygon (Sting ray). .
. . Class – Osteichthyes Class – Osteichthyes Class – Osteichthyes Class – Osteichthyes Class – Osteichthyes It includes both marine and fresh water fishes with bony endoskeleton. Their body is streamlined.
Mouth is mostly terminal (Figure . ). They have four pairs of gills which are covered by an operculum on each side. Skin is covered with cycloid/ctenoid scales.
Air bladder is present which regulates buoyancy. Heart is two- chambered (one auricle and one ventricle). They are cold-blooded animals. Sexes are separate.
Fertilisation is usually external. They are mostly oviparous and development is direct. Examples: Marine – Exocoetus (Flying fish), Hippocampus (Sea horse); Freshwater – Labeo (Rohu), Catla (Katla), Clarias (Magur); Aquarium – Betta (Fighting fish), Pterophyllum (Angel fish). .
. . Class – Amphibia Class – Amphibia Class – Amphibia Class – Amphibia Class – Amphibia As the name indicates ( Gr., Amphi : dual, bios , life), amphibians can live in aquatic as well as terrestrial habitats (Figure . ).
Most of them have two pairs of limbs. Body is divisible into head and trunk. Tail may be present in some. The amphibian skin is moist (without scales).
The eyes have eyelids. A tympanum represents the ear. Alimentary canal, urinary and reproductive tracts open into a common chamber called cloaca which opens to the exterior. Respiration is by gills, lungs and through skin.
The heart is three- chambered (two auricles and one ventricle). These are cold-blooded animals. Sexes are separate. Fertilisation is external.
They are oviparous and development is indirect. Examples: Bufo (Toad), Rana (Frog), Hyla (Tree frog), Salamandra (Salamander), Ichthyophis (Limbless amphibia). Figure . Examples of Amphibia : (a) Salamandra (b) Rana Figure .
Examples of Bony fishes : (a) Hippocampus (b) Catla . . . .
. . . Class – Reptilia Class – Reptilia Class – Reptilia Class – Reptilia Class – Reptilia The class name refers to their creeping or crawling mode of locomotion (