The below mentioned article provides biology notes on Class Osteichthyes. 1. The endoskeleton is cartilaginous in the embryonic stage, but in the adult forms more or less it is replaced by bones. Thus they have bony endoskeleton. They are ectothermic (cold blooded). There are about 25,000 species of bony fishes. 2. Caudal fin usually homocercal symmetrical (Gr. homos- alike). 3. [...]
The below mentioned article provides short notes on Class Chondrichtyes. 1. The fishes of this class bear cartilaginous endoskeleton. They are cold blooded (poikilothermous or ectothermic). There are about 600 species of cartilaginous fishes. 2. The skin is tough, containing minute placoid scales, which are dermal in origin. 3. Except in the Chimaeras, the gills are not covered by an [...]
In this article we will discuss about the General Characters and Classification of Phylum Platyhelminthes. General Characteristics of Phylum Platyhelminthes: (Gk. platys- broad or flat; helminworm) Gegenbaur (1859) placed flat worms in a separate group and gave the term Platyhelminthes. The phylum Platyhelminthes includes about 13,000 species. General Characters: 1. Habitat: The flat worms arc mostly parasites but some flat [...]