- For other uses, see phyla.
In biological taxonomy, a phylum (Greek Φῦλον plural: Φῦλα phyla) is a taxon in the rank below kingdom and above class. "Phylum" is adopted from the Greek φυλαί phylai, the clan-based voting groups in Greek city-states. Phyla represent the largest generally accepted groupings of animals and other living things with certain evolutionary traits, although the phyla themselves may sometimes be grouped into superphyla (e.g. Ecdysozoa with eight phyla, including arthropods and roundworms; and Deuterostomia with the echinoderms, chordates, hemichordates and arrow worms). Informally, phyla can be thought of as grouping animals based on general body plan[1]; this is morphological grouping. Thus despite the seemingly different external appearances of organisms, they are classified into phyla based on their internal organizations[2]. For example, though seemingly divergent, spiders and crabs both belong to Arthropoda, whereas earthworms and tapeworms, similar in shape, are from Annelida and Platyhelminthes, respectively. Although the International Code of Botanical Nomenclature allows the use of the term "Phylum" in reference to plants, the term "Division" is almost always used by botanists.
The best known animal phyla are the Mollusca, Porifera, Cnidaria, Platyhelminthes, Nematoda, Annelida, Arthropoda, Echinodermata, and Chordata, the phylum to which humans belong. Although there are approximately 35 phyla, these nine include the majority of the species. Many phyla are exclusively marine, and only one phylum is entirely absent from the world's oceans: the Onychophora or velvet worms. The most recently discovered phylum is Cycliophora[3] found in 1993; only three phyla were discovered in the last century.
The Cambrian explosion was a great flowering of life forms that occurred between roughly 530 and 520 million years ago;[4] during this time organisms similar to, but not strictly members of, modern phyla existed;[5] whilst some appear to be represented in the Ediacaran biota, it remains a matter of debate whether all phyla existed prior to the explosion. Over time the roles among different phyla have varied. For instance, during the Cambrian, the dominant megafauna, or large animals, were arthropods, whereas now the megafauna is dominated by vertebrates (chordata).[6] The arthropods are still by far the most dominant phylum.
List of animal phyla
Phylum | Meaning | Group | Distinguishing characteristics | Species described |
Acanthocephala | Thorny head | Thorny-headed worms | Reversible spiny proboscis | about 1,151 |
Acoelomorpha | Without gut | Acoels | No mouth or alimentary canal |
Annelida | Little ring | Segmented worms | Multiple circular segments | about 15,000 modern |
Arthropoda | Jointed foot | Arthropods | Chitin exoskeleton | 1,134,000+ |
Brachiopoda | Arm foot | Lamp shells | Lophophore and pedicle | between 300 and 500 extant |
Bryozoa | Moss animals | Moss animals, sea mats | Lophophore, no pedicle, ciliated tentacles | about 5,000 living species |
Chaetognatha | Longhair jaw | Arrow worms | Chitinous spines either side of head, fins | about 100 modern species |
Chordata | Cord | Chordates | Hollow dorsal nervous chord | about 100,000+ |
Cnidaria | Stinging nettle | Coelenterates | Nematocysts (stinging cells) | about 11,000 |
Ctenophora | Comb bearer | Comb jellies | Eight "comb rows" of fused cilia | about 100 modern species |
Cycliophora | Wheel carrying | Symbion | Circular mouth surrounded by small cilia | at least 3 |
Echinodermata | Spiny skin | Echinoderms | Five-fold radial symmetry, mesodermal calcified spines | about 7,000 living species and 13,000 extinct ones |
Echiura | Spine tail | Spoon worms | Set of hooks at posterior end | about 140 |
Entoprocta | Inside anus | Goblet worm | Anus inside ring of cilia | about 150 |
Gastrotricha | Hair stomach | Meiofauna | Two terminal adhesive tubes | about 690 |
Gnathostomulida | Jaw orifice | Jaw worms |
| about 100 |
Hemichordata | Half cord | Acorn worms | Stomochord in collar | about 100 living species |
Kinorhyncha | Motion snout | Mud dragons | Eleven segments, each with a dorsal plate | about 150 |
Loricifera | Corset bearer | Brush heads | Umbrella-like scales at each end | about 122 |
Mesozoa | Middle animals | Mesozoans | Somatoderm of ciliated cells surrounding reproductive cell(s) |
|
Micrognathozoa | Tiny jaw animals | — | Accordion like extensible thorax | 1 |
Mollusca | Thin shell | Mollusks / molluscs | Muscular foot and mantle round shell | 112,000[7] |
Myxozoa | Slime animals |
| Polar capsules resembling nematocysts | 13,000+ |
Nematoda | Thread like | Round worms | Round cross section, keratin cuticle | 80 000 - 1 million |
Nematomorpha | Thread form | Horsehair worms |
| about 320 |
Nemertea | A sea nymph | Ribbon worms |
| about 1200 |
Onychophora | Claw bearer | Velvet worms | Legs tipped by chitinous claws | about 200 modern |
Orthonectida | Straight swim |
|
| about 20 |
Phoronida | Zeus' mistress | Horseshoe worms | U-shaped gut | 20 |
Placozoa | Plate animals |
|
| 1 |
Platyhelminthes | Flat worms | Flat worms |
| about 25,000[8] |
Porifera | Pore bearer | Sponges | Perforated interior wall | over 5,000 modern |
Priapulida | Penis | Priapulid worms | Retractable proboscis surrounded by papillae | 17 |
Rhombozoa | Lozenge animal | — | Single axial cell surrounded by ciliated cells | 75 |
Rotifera | Wheel bearer | Rotifers | Anterior crown of cilia | about 2000 |
Sipuncula | Small tube | Peanut worms | Mouth surrounded by invertible tentacles | 144-320 |
Tardigrada | Slow step | Water bears | Four segmented body and head | 1,000+ |
Xenoturbellida | Strange flatworm | — | Ciliated deuterostome | 2 |
TOTAL |
|
|
| 2,000,000- |
Groups formerly ranked as phyla
List of plant divisions
List of fungi divisions
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