Key Features and Classifications of Animal Life

Multicellular

Organisms composed of multiple cells.

Heterotrophic

Organisms that consume other organisms for energy.

Lack cell walls

Characteristic of animals that differentiates them from plants and fungi.

Radial Symmetry

Symmetry around a central axis; can be divided into similar halves by multiple planes.

Bilateral Symmetry

Only one plane splits the body into mirror-image halves.

Protostomes

Organisms where the mouth develops first from the embryonic opening (blastopore).

Deuterostomes

Organisms where the anus develops first from the blastopore.

Choanocytes

Specialized cells with flagella that drive water through the sponge and trap food.

Amoebocytes

Cells that digest food and transport nutrients in sponges.

Porocytes

Cells that form pores in sponges.

Eumetazoa

Organisms with true tissues and organized body structures, such as nerve and muscle tissues.

Parazoa

Organisms without true tissues, exemplified by sponges.

Cnidocytes

Stinging cells that define cnidarians.

Spiralia

Organisms that grow by adding body mass and exhibit spiral cleavage during embryonic development.

Platyzoans

Organisms characterized by flat body shapes and simple body plans.

Phylum Mollusca

A group of animals with bodies divided into head-foot, visceral mass, and mantle.

Radula

A feeding structure found in most mollusks.

Gastropoda

A class of mollusks that includes snails and slugs.

Bivalvia

A class of mollusks that includes clams and oysters.

Cephalopoda

A class of mollusks that includes octopuses and squids, known for their intelligence and jet propulsion.

Polyplacophora

A class of mollusks known as chitons.

Polychaeta

A class of annelids that are mostly marine and have many bristles.

Clitellata

A class of annelids that includes earthworms and leeches.

Ecdysozoans

Organisms that grow by molting their exoskeleton.

Nematodes

Roundworms that are mostly parasitic, with some being free-living.

Ascariasis

An intestinal infection caused by nematodes.

Trichinosis

A disease caused by undercooked meat containing nematodes.

Filarial diseases

Diseases caused by nematodes that block lymph vessels, such as elephantiasis.

Arthropods

Organisms with segmented bodies, jointed appendages, and exoskeletons made of chitin.

Chelicerata

A class of arthropods that includes spiders and scorpions.

Myriapoda

A class of arthropods that includes centipedes and millipedes.

Crustacea

A class of arthropods that includes crabs and lobsters.

Hexapoda

A class of arthropods that includes insects.

Advantages of Exoskeleton

Protection from predators, waterproof barrier, support for muscles.

Drawbacks of Exoskeleton

Limits growth due to molting and can be heavy relative to size if large.