Class Cyclostomata
- All are ectoparasites on some fishes.
- Elongated body without scales and paired fins.
- 6-15 pairs of gill slits for respiration.
- Sucking and circular mouth without jaws.
- Cartilaginous cranium and vertebral column.
- Circulation is closed type.
- Marine, but migrate for spawning to fresh water. After spawning, they die. Their larvae, after metamorphosis, return to ocean.
- E.g., Petromyzon (Lamprey), Myxine (Hagfish)
Superclass Pisces (Fishes)
Class Chondrichthyes (Cartilaginous Fishes)
- Marine. Stream-lined body. Predaceous.
- Cartilaginous endoskeleton.
- Notochord is persistent throughout life.
- Ventral mouth.
- Gill slits without operculum. Powerful jaws.
- Skin with placoid scales. Teeth are modified placoid scales which are backwardly directed.
- No air bladder. So, they have to swim constantly to avoid sinking.
- Poikilotherms (Cold-blooded animals): Animals that lack the capacity to regulate their body temperature.
- Two-chambered heart (one auricle and one ventricle).
- Sexes are separate. In males, pelvic fins bear claspers. Internal fertilization. Many of them viviparous.
- Examples:
- Scoliodon (Dogfish)
- Pristis (Saw Fish)
- Carcharodon (Great White Shark)
- Trygon (Sting Ray - has poison sting)
- Torpedo (Electric Ray - has electric organ)
Class Osteichthyes (Bony Fishes)
- Marine & fresh water. Stream-lined body.
- Bony endoskeleton.
- Terminal mouth.
- 4 pairs of gills covered by operculum on each side.
- Scales are cycloid, ctenoid, etc.
- Air bladder for buoyancy.
- Poikilotherms (cold-blooded).
- Two-chambered heart (one auricle and one ventricle).
- Sexes are separate. External fertilisation.
- Mostly oviparous. Development is direct.
- Examples:
- Marine: Exocoetus (Flying Fish), Hippocampus (Seahorse)
- Fresh Water: Labeo (Rohu), Catla (Katla), Clarias (Magur)
- Aquarium: Betta (Fighting Fish), Pterophyllum (Angel Fish)
