Sponges
Sponges have no true tissues or organs. [source]
The major animal groups
A whistle-stop tour of the big branches, from animals that are barely more than plumbing to the ones reading this sentence.
Eight phyla worth knowing
Cnidarians
Cnidarians (jellyfish, corals, anemones) number over 11,000 species. [source]
Segmented worms
Annelids — segmented worms — number over 22,000 species. [source]
Molluscs
Molluscs are the second-largest animal phylum, with about 86,600 known species. [source]
Arthropods
Arthropods make up over 80 per cent of described living animal species. [source]
About 400,000 beetle species have been described — roughly 40 per cent of described insects. [source]
Tardigrades
About 1,500 tardigrade species have been described. [source]
Echinoderms
There are about 7,600 living species of echinoderm, all of them marine. [source]
Chordates
Chordates number over 81,000 species, about half of them ray-finned fishes. [source]
The vertebrate classes
Birds are living dinosaurs — the surviving branch of the theropods. [source]
Fish
There are over 33,000 described fish species. [source]
Amphibians
AmphibiaWeb lists 9,149 amphibian species: 8,068 frogs and toads, 846 newts and salamanders, 235 caecilians (22 Oct 2026). [source]
Reptiles
The Reptile Database lists about 12,000 reptile species. [source]
Birds
There are over 11,000 living bird species. [source]
Mammals
There are about 6,640 mammal species in 27 orders. [source]