An Overview of the Invertebrates
Life on Earth evolved from single-celled oragnisms that lived in the oceans around 3,500 million years ago. Jellyfish, simple worms and other multicellular animals later evolved in the seas followed by creatures with hard outsides, such as shellfish and trilobites. These are the primitive arthropods (Phylum: Arthropoda).
These arthropods later became the first land animals, emerging from the oceans as scavengers about 420 million years ago. The co-evolution of land plants provided resources for numerous different arthropod species, the most successful being the insects.
Today, invertebrates (animals without a backbone) make up 97% of living animals. Vertebrates (animals with a backbone) make up the remainding 3%. Within the invertebrates, the huge group Arthropoda contains the majority of species - over 1 million.
The Phyla of the
Animal Kingdom showing scientific names, common names and number of species
Phylum Placozoa Placozoa 1
Phylum
Porifera Sponges 10 000
Phylum
Cnidaria Sea Anemones, Jellyfishes
9 500
Phylum Ctenophora Comb Jellies 90
Phylum
Platyhelminthes Flat Worms 25 000
Phylum
Mesozoa Mesozoa 50
Phylum
Nemertina Ribbon Worms 900
Phylum
Gnathostomulida Sand Worms
80
Phylum
Gastrotricha Gastrotrichs 400
Phylum
Rotifera Rotifers 2000
Phylum
Nematoda Nematodes 80 000
Phylum
Nematomorpha Horsehair Worms 240
Phylum
Kinorhyncha Spiny-crown Worms
100
Phylum
Loricifera Brush Heads 10
Phylum
Acanthocephala Spiny-headed Worms
1 000
Phylum
Cycliophora Cycliophorans 1
Phylum
Entoprocta Marine Mats 150
Phylum
Ectoprocta Bryozoans 5 000
Phylum
Phoronida Phoronans 10
Phylum
Brachiopoda Lamp Shells 335
Phylum
Mollusca Slugs, Snails, Squid. 110 000
Phylum
Priapulida Phallus Worms
16
Phylum
Sipuncula Peanut Worms
320
Phylum
Echiura Spoon Worms
140
Phylum
Annelida Earthworms, Ragworms 9 000
Phylum
Tardigrada Water Bears 700
Phylum
Pentastoma Tongueworms 70
Phylum
Onychophora Peripatus 80
Phylum
Pogonophora Beard Worms
120
Phylum
Echinodermata Starfish and allies 6 000
Phylum
Chaetognatha Arrow-worms 110
Phylum
Hemichordata Hemichordates 90
Phylum
Chordata Chordates (Tunicates, Mammals, Birds etc.) 50 000