Revision: Class 11 >> Animal Kingdom NEET (UG) Animal Kingdom

Small pores through which water enters the body of a sponge are called ostia.

A large opening through which water exits the body of a sponge is called an osculum.

Special types of cells present in sponges that help in generating water current and food collection are called collar cells.

Coelom: Coelom is the internal body cavity between visceral organs and body wall in which well-developed organs can be accommodated. In some animals pseudocoelom is present (e.g. nematodes) which is a body cavity not lined by mesoderm. True coelom is lined by mesoderm and first appears in annelids. Examples of animals in which true coelom is present are Earthworm, cockroach, snail, all chordates such as birds, humans, etc.

A cylindrical body form in coelenterates, such as Hydra, which is usually attached to a surface, is called a Polyp.

An umbrella-shaped body form in coelenterates, such as Aurelia (jellyfish), is called a Medusa.

• Habitat: Aquatic animals, mostly marine and few freshwater species
• Body Symmetry: Mostly asymmetrical
• Special Features: Presence of pores (ostia and oscula), collar cells, and sedentary (non-motile) nature
• Body Support: Supported by spicules or spongin fibres made of calcium carbonate or silica
• Reproduction: Asexual (by budding) and sexual methods; good regeneration ability
• Examples: Sycon, Euspongia (Bath sponge), Hyalonema, Euplectella

• Body Shape: Cylindrical (Polyp) or umbrella-like (Medusa)
• Habitat: Mostly marine; few are freshwater dwellers
• Body Structure: Radially symmetrical and diploblastic
• Special Feature: Tentacles with cnidoblasts used for capturing prey and injecting toxins
• Examples: Hydra, Adamsia (Sea anemone), Physalia (Portuguese man-of-war), Aurelia (Jellyfish), Corals

• Body Shape: Slender, flat like a leaf or strip (called flatworms)
• Habitat: Mostly endoparasitic; few are free-living and aquatic
• Body Structure: Acoelomate, bilaterally symmetrical, and triploblastic
• Reproduction: Hermaphrodite – both male and female systems in one body
• Examples: Planaria, Liver fluke, Tapeworm

• Body Shape: Long, thread-like or cylindrical (called roundworms)
• Habitat: Free-living (aquatic or terrestrial) or endoparasitic
• Body Structure: Triploblastic, pseudocoelomate, non-segmented, with a tough cuticle
• Reproduction: Unisexual – male and female are separate
• Examples: Ascaris (intestinal worm), Filarial worm, Loa loa (eye worm)

• Body Structure: Long, cylindrical, metamerically segmented
• Habitat: Mostly free-living (marine, freshwater, or terrestrial); some are ectoparasites
• Body Type: Triploblastic, bilaterally symmetrical, and eucoelomate
• Locomotion: Movement with setae, parapodia, or suckers
• Reproduction: Hermaphrodite or unisexual
• Examples: Earthworm, Leech, Nereis

• Body Structure: Segmented, triploblastic, eucoelomate, and bilaterally symmetrical
• Appendages: Jointed appendages with a chitinous exoskeleton
• Habitat: Found in all types of environments – aquatic, terrestrial, and aerial
• Reproduction: Unisexual
• Examples: Crab, spider, cockroach, butterfly, honey bee

• Body Structure: Soft, non-segmented, triploblastic, eucoelomate body
• Symmetry: Bilateral (except in some, like snail)
• Body Division: Head, foot, and visceral mass covered by a mantle
• Shell: Hard, calcareous shell (may be external, internal, or absent)
• Reproduction: Unisexual
• Examples: Bivalve, Snail, Octopus

• Body Structure: Triploblastic, eucoelomate, radially symmetrical in adults and bilaterally symmetrical in larvae
• Habitat: Exclusively marine
• Locomotion: Tube feet are used for movement and capturing prey; some are sedentary
• Skeleton: Made of calcareous spines and ossicles
• Reproduction: Mostly unisexual
• Examples: Starfish, sea urchin, sea cucumber, brittle star

• Body Structure: Divided into proboscis, collar, and trunk.
• Notochord: Present only in the proboscis region, hence the name hemichordates.
• Habitat: Marine animals that live in burrows in sand.
• Respiration: Possess one to many pharyngeal gill slits.
• Reproduction: Mostly unisexual, though some may be hermaphrodite.
• Examples: Balanoglossus, Saccoglossus.
• Evolutionary Importance: Balanoglossus is considered a connecting link between non-chordates and chordates.

• Notochord: Replaced by vertebral column
• Head: Well developed
• Brain Protection: Enclosed in a cranium
• Endoskeleton: Cartilaginous or bony
• Jaw Type: Some are jawless (Agnatha), others have jaws (Gnathostomata)

• Mouth: Jawless, with sucker
• Skin: Soft, without scales
• Appendages: Paired appendages absent
• Endoskeleton: Cartilaginous
• Lifestyle: Mostly ectoparasitic
• Examples: Petromyzon, Myxine

• Life Stages: Aquatic larva (with aquatic respiration); adult lives on land and water
• Appendages: Two pairs, digits without claws
• Skin: Moist, without scales
• Respiration: Both aquatic and aerial in adults
• Sensory Organs: Tympanum present, external ear absent, eyelids present
• Examples: Frog, Toad, Salamander

• Movement: Creeping (body cannot be fully lifted)
• Temperature Regulation: Cold-blooded (Poikilotherms)
• Skin: Dry and scaly
• Neck: Present
• Digits: With claws
• External Ear: Absent
• Examples: Tortoise, Lizard, Snake

• Temperature Regulation: Warm-blooded (Homeotherms)
• Body Structure: Spindle-shaped to reduce air resistance
• Forelimbs: Modified into wings
• Exoskeleton: Feathers; digits with scales and claws
• Jaws: Modified into beak
• Neck: Present
• Examples: Peacock, Parrot, Duck, Penguin

• Unique Feature: Mammary glands present
• Temperature Regulation: Warm-blooded
• Body Division: Head, neck, trunk, tail
• Digits: Provided with nails, claws, or hooves
• Exoskeleton: Hair or fur
• Examples: Elephant, Human, Kangaroo, Dolphin