There are stinging cells on the body surface, the radiation is symmetrical, there is a mouth but no anus.

Hydra

Symmetrical on both sides, flat dorsally and ventrally, with mouth but no anus

planarian

Cylindrical, with cuticle, mouth and anus, slender body

roundworms

It is cylindrical in shape, and its body is composed of similar segments. Its movement is assisted by setae or warts.

earthworm

Leeches: extract hirudin

There is a mantle on the surface of the soft body, most of which have shells. The locomotor organs are feet.

Razor clam: open in and close out

locust

Crustaceans: shrimp, crab, etc.

Myriapods: centipedes, etc.

Arachnids: Spiders, etc.

Living in water, breathing through gills, relying on the swing of the tail and trunk and the coordination of the fins

The body is streamlined to reduce the resistance of the fish when swimming in the water

The body is covered with scales that secrete mucus to protect the body

The function of fish tail fin: control direction and provide power

Respiratory organs of fish: gills

Metamorphosis develops. The larvae live in water and breathe with gills. The adults live on land and can also swim in water and breathe with lungs. The skin can assist breathing.

frog

There are horny scales or nails on the body surface, and there are sharp and tough egg shells on the surface of the eggs. They use lungs to breathe.

Reproduction and development free from dependence on water

The function of horny scales or nails: to prevent the loss of water in the body

The body is streamlined to reduce drag in the air

The body surface is covered with feathers, and the forelimbs become wings.

Bones are light, thin, strong, long bones are hollow

Short rectum, no bladder, weight loss

Breathing method: double breathing, the air bag can assist breathing, but it is not used as a place for gas exchange

warm-blooded animals

Body surface covered with hair, viviparous, lactating, teeth including canines, incisors, and molars.

Incisors: bite off food

Viviparous breastfeeding greatly improves the survival rate of offspring

The components of the movement system: bones (levers), joints (fulcrums), skeletal muscles (power)

Joint: joint head, glenoid fossa, joint capsule, articular cartilage, joint cavity

Structures related to joint stability: joint capsule, ligaments

Composition of skeletal muscle: muscle bellies and tendons

When the elbow is flexed, the biceps brachii contracts and the triceps brachii relaxes; when the elbow is extended, the biceps brachii relaxes and the triceps brachii contracts.

innate sexual behavior

learning behavior