Here are some examples of animal groups that have organ system level of organization:
* Cnidaria: Jellyfish, corals, sea anemones
* Platyhelminthes: Flatworms
* Nematoda: Roundworms
* Annelida: Segmented worms (earthworms, leeches)
* Mollusca: Snails, clams, octopuses
* Arthropoda: Insects, spiders, crustaceans
* Echinodermata: Starfish, sea urchins
* Chordata: Vertebrates (fish, amphibians, reptiles, birds, mammals) and invertebrates (tunicates, cephalochordates)
Organ system level of organization means that the animal's body is composed of different organs that work together to perform specific functions. These organs are made up of different tissues, and tissues are made up of cells. Here are some examples of organ systems:
* Digestive system: Breaks down food
* Circulatory system: Transports blood and nutrients
* Respiratory system: Takes in oxygen and releases carbon dioxide
* Nervous system: Controls and coordinates body functions
* Excretory system: Removes waste products
The presence of organ systems allows animals to perform more complex functions and to adapt to a wider range of environments than animals that only have tissue or cell level organization.
