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Animal Phyla

Last updated about 2 years ago

The major subgroups of animals are usually classified as phyla (singular: phylum). The higher classification of animals is still in flux, and scientists' opinions on which groups should be given phylum status change as new information about the structure of the animal tree of life becomes available. So you may see that some of the groups listed here as phyla are classified differently elsewhere. For example, the spiny-headed worms, Acanthocephala used to be treated as a phylum, but research has shown that this group is probably nested within the phylum Rotifera, so it will probably disappear from modern lists of animal phyla.

Follow the links below to find out more about each animal phylum. Species estimates are from:

Chapman, A. D. 2009. Numbers of Living Species in Australia and the World. 2nd edition. Australian Government, Department of the Environment, Water, Heritage and the Arts. Canberra, Australia.

Zhang, Z.-Q. 2011. Animal biodiversity: An introduction to higher-level classification and taxonomic richness. Zootaxa 3148: 7–12.

Want a fun way to practice recognizing animal phyla? Play the Animal Phyla Memory Game

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    Spiny-headed Worms

    Obligate intestinal parasites of vertebrates. Most acanthocephalans are less than 20 cm long, although a few exceed 60 cm. 1,194 species, including 2 fossil species.

    Recent evidence indicates that acanthocephalans are not an independent phylum but rather an unusual group of rotifers.

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    Small, marine, soft-bodied flattened worms lacking a gut and anus. Most are free-living. 393 species.

    Acoel worms used to be placed in the phylum Platyhelminthes, but molecular data have shown that they are not a part of this group. Recent evidence indicates that Acoelomorpha are closely related to the enigmatic Xenoturbella, and the two groups are sometimes combined as subphyla in the phylum Xenacoelomorpha.

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    Segmented Worms

    Includes earthworms, leaches and marine segmented worms. Echiura, Pogonophora, and Sipuncula, which used to be independent phyla, are now part of Annelida. 17,590 species.

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    Includes terrestrial groups like insects, spiders, millipedes, centipedes as well as predominantly marine groups like crustaceans and sea spiders. 1,242,040 species, including 6,182 fossil species. Many species have yet to be discovered.

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    Lamp Shells

    Marine suspension feeders that superficially resemble mussels due to their hard shells. 443 living species. Many more extinct species.

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    Moss Animal

    Also sometimes called ectoprocts. Predominantly marine suspension feeders, but some in freshwater environments. Most bryozoans live in sessile colonies that resemble algae or corals. 10,941 species, including 5,455 fossil species.

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    Arrow Worms

    Planktonic (floating in the water column) and benthic (bottom-dwelling) marine predators. 186 species, including 7 fossil species

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    Includes the well-known vertebrates (fishes, amphibians, reptiles, birds, mammals) as well as tunicates (Urochordata) and lancelets (Cephalochordata). 64,791 living species, many fossil vertebrate species.

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    Predominantly marine predators, but some live in freshwater. Found as sessile polyps or free-living medusae. Includes hydras, sea fans, jellyfishes, sea anemones, corals. 10,105 living species, many fossil species.

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    Comb Jellies

    Gelatinous marine animals. Predators feeding on zooplankton such as fish eggs, copepods, amphipods, and larvae. 242 species.

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    Tiny marine animals that live in close association with lobsters. 2 species

    Cycliophorans are most likely related to entoprocts and bryozoans.

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    Entirely marine, includes sea stars, brittle stars, sea urchins, sand dollars, sea cucumbers, and sea lilies. 20,509 species, including 13,000 fossil species

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    Goblet Worms

    Small, transparent, sessile, mostly marine suspension feeders. May be solitary or colonial. 169 species

    Entoprocts are probably closely related to cycliophorans and bryozoans.

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    Very small, worm-like animals. Live in marine, brackish, and freshwater habitats. 790 species

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    Jaw Worms

    Translucent microscopic, interstitial (i.e., living between sediment particles) marine worms. 109 species

    Gnathostomulids are probably closely related to rotifers.

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    Soft-bodied, benthic (bottom-dwelling) marine animals. 120 species

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    Mud Dragons

    Microscopic worm-like animals. Most live in marine sand or mud from the intertidal zone. 179 species.

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    Microscopic animals that live between the particles of marine sediments. 30 species.

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    A microscopic animal, discovered living in homothermic springs on Disko Island, Greenland. 1 species

    This group is most likely closely related to rotifers.

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    Includes snails, slugs, clams, mussels, squid, and octopuses. Most are marine, but also many terrestrial and freshwater species. 117,358 species

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    Most are free-living worms in soil or aquatic sediment (sand or mud) but many species are parasites of plants and animals. 24,783 species, including 10 fossil species. Many species have yet to be discovered.

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    Horsehair Worms

    Parasitic worms. Attack insects and other arthropods. Reproduce in freshwater environments. 351 species.

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    Ribbon Worms

    Mostly marine, unsegmented, predatory worms. 1,200 species

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    Velvet Worms

    Caterpillar-like relatives of arthropods. Predators found in humid terrestrial habitats. 182 species, including 3 fossil species

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    Microscopic parasites of marine invertebrates like flatworms, polychaete worms, bivalve molluscs, and echinoderms. 43 species.

    The relationships of this group to other animals are unclear.

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    Horseshoe Worms

    Sessile, worm-like, marine suspension feeders. 10 species

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    Small marine animals. The structurally simplest metazoan. 1 species

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    Unsegmented, soft-bodied worms. Many parasitic species. Free-living species in marine, freshwater, and humid terrestrial environments. 29,285 species

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    Aquatic filter-feeders. 8,346 species

    Sponges may not be a natural group (monophyletic). Some sponges may be more closely related to other animals than to other sponges.

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    Penis Worms

    Free-living benthic (bottom-dwelling) marine worms. 19 species.

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    Tiny parasites that live in the renal appendages of cephalopods. 123 species.

    The relationships of this group to other animals are unclear.

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    Tiny sessile or free-swimming animals. Inhabit freshwater, marine, or semi-terrestrial environments. 1,583 species.

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    Peanut Worms

    Marine invertebrate worms. 144 species

    Recent evidence indicates that sipunculans are not an independent phylum but rather an unusual group of annelids.

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    Water Bears

    Small, water-dwelling, segmented animals. Inhabit a variety of wet or moist habitats, including marine and freshwater, moist soils, hot-springs, glaciers, mosses, lichens, leaf-litter. 1,157 species

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    Strange Worms

    Ciliated marine worms. 2 species

    Recent evidence indicates that Xenoturbella is closely related to Acoelomorpha, and the two groups are sometimes combined as subphyla in the phylum Xenacoelomorpha.