List of animal phyla
List of animal phyla is a list of the major groups af animals usually classified as a phylum. Modern sources have been used: the list is different from that of Linnaeus or Cuvier. A list of this type may be arranged alphabetically; but equally it might be arranged according to evolutionary relationships. No list will be completely satisfactory. Authorities differ in what they consider a phylum, and in the actual name of the phylum. Despite this, there is agreement on most phyla. Most modern surveys include groups above the phylum: superphyletic groupings based on evidence of common descent.
Differences of opinion about evolutionary relationships have been reduced by the use of molecular evolution and molecular clock research. These make use of protein amino acid sequences, and whole genome DNA sequence analysis. These modern techniques have led to changes and renaming of many higher categories. Classification based on traditional comparative anatomy had errors which needed to be corrected. So, for example, the old phylum Coelenterata, which had stood for almost two hundred years, was split down into two separate phyla, the Cnidaria and the Ctenophora.
Major groups in large type.
- Choanoflagellata: 140 species of single-celled flagellates some of which form colonies. They do not have chloroplasts, so they are heterotrophic. They are sometimes classified as protista. If animals, then they are a minor phylum.
- Porifera: the sponges. 5000 species, aquatic metazoa. Have collared cells with long cilia. Sessile, have cell differentiation. Skeleton are of spongin, or are calcareous CaCO3, or silicious SiO2.
- Placozoa: only one species known, Trichoplax adhaerens, discovered in 1883. Small, about 2mm, aquatic, eats bacteria and single-celled algae & protozoa. Obviously, a minor phylum.
- Cnidaria: a large and important phylum, with an extensive fossil record. 10,000 living species. Aquatic, mainly marine, five classes: Anthozoa (sea anemones, corals); Scyphozoa (true jellyfish); Cubozoa (box jellies); Hydrozoa: the hydroids; Staurozoa (stalked jellyfish). Larvae are planulas; or (star fish) bipinnaria, then brachiolaria.
- Ctenophora: the comb jellies. Eight comb rows of fused cilia. 80 living marine species: pelagic, transparent and rather beautiful. A minor phylum.
- Sipuncula: 150 species, no certain fossil record. Small, tube-like marine animals with long tentacle-like front part which can be pulled in or out. The mouth is surrounded by a ring of cilia. Has pelagic larvae. A minor phylum.
- Mollusca: a great phylum by number of species and by variety of body forms; largely aquatic. Hugely important fossil record from the Lower Cambrian. A major food source for mankind, second only to fish. United by their mantle, the muscular 'foot', the radula (teeth band), and (ancestrally) by the shell. Number of living species estimated as 50,000 to 150,000. Classes: lesser classes are the Aplacophora, Monoplacophora, and Polyplacophora. Major classes are the Gastropods, Cephalopods, Bivalves and Scaphopods. A familiarity with bivalve evolution is valuable for identifying strata, so common are their fossils. Larvae are trochophores; or veligers (many gastropods & bivalves); glochidium (some freshwater bivalves).
- Annelida: important phylum of both aquatic and terrestrial segmented worms. At least 15,000 living species. Fossil record weak, evolutionary history not well known. Classes: Polychaeta (marine worms), Oligochaeta (earthworms), Hirudinea (leeches). Larvae are trochophores or nectochaeta.
- Onychophora: the velvet worms. Only 110 species from two families, they are relatives of the Arthropods. A minor phylum.
- Arthropoda: by far the largest phylum. A recent estimate of the number of arthropods on Earth today is 3.7 million species. It includes animals with jointed limbs and an exoskeleton made of chitin. There are many opinions about its classification. An arrangement found in several texts is: Superphylum Arthropoda: Phyla Chelicerata, Crustacea, Uniramia (Insects + Myriapoda).p61 If Arthropoda is ranked as a phylum, its subdivisions rank as Subphyla:
- Trilobitomorpha: the trilobites, Cambrian to Permian. Sometimes classed as Crustacea.
- Chelicerata. Classes Arachnida: the spiders, mites, scorpions. Xiphosura: horseshoe crab Limulus. Pycnogonida: sea spiders. Eurypterida: sea scorpions (extinct).
- Myriapoda. Classes: Chilopoda: centipedes. Diplopoda: millipedes. Symphyla and Pauropoda: minor groups.
- Hexapoda. Two Classes of hugely different size. Insecta: the insects; overwhelmingly the most common terrestrial animals, with an estimated 1.5 to 3 million species in about 30 orders. Apterygota are the wingless insects. Development of insects involves many kinds of larvae, both aquatic and terrestrial and, almost always, metamorphosis. The other class, the Entognatha consists of three small groups.
- Crustacea. Classes: Branchiopoda: brine shrimps. Cephalocarida: horseshoe shrimps. Maxillopoda: barnacles, fish lice. Ostracoda: seed shrimps. Malacostraca: lobsters, crabs, shrimp. Remipedia: a group of blind underground crustacea, globally distributed but confined to coastal aquifers. First larva is usually a nauplius, which may be followed by other larval stages.
- Tardigrada: 'Water bears'. 700 species of microscopic animals from damp or aquatic habitats. Structure is constant: head, four segments, each with two legs. Terrestrial species are adapted to survive extreme conditions. A minor phylum.
- Bryozoa, also known as the Ectoprocta: An aquatic phylum with a huge fossil record (one of the most common in the Palaeozoic). Still fairly common, though little known to the public. There are now 5000 species, most of which build calcareous skeletons. They are almost all colonial, and all their zooids are clones.
- Entoprocta: A small phylum (150 species) of sessile benthic marine animals. A minor phylum.
- Platyhelminthes: the flatworms. Classes: Turbellaria: free-living and aquatic (4,500 species); Trematoda: parasitic flukes of molluscs and vertebrates (~1500 species); Cestoda: tapeworms, parasitic in the digestive tract of vertebrates (3400 species); Monogenea: ectoparasites on the gills and skin of fish (1100 species). Müller's larva is characteristic of the free-living species, but in the parasitic groups development may be direct.
- Nemertea or Nemertini: flat, unsegmented ribbon worms, mostly aquatic. They have also been called Rhynchocoela or proboscis worms. About 1400 species. There have been reports of extremely long ribbon worms, unconfirmed. Larvae are pilidiums. A minor phylum.
- Rotifera: the rotifers. The rotifers (2200 species) are everywhere in transient pools and in sea and fresh water. The ring of cilia circling the mouth and the protective lorica are distinctive. The phylum now includes the Acanthocephala, parasitic thorn-headed worms.
- Cycliophora: a recently discovered group of tiny animals which live on lobsters. One genus and three species so far. A minor phylum.
- Gastrotricha: another phylum of small aquatic animals, with about 700 species. They are bilateral with a complete gut. They are covered with cilia, and have two terminal glands. One gland secretes cement, the other dissolves it. They have a short life span of a few days. A minor phylum.
- Gnathostomulida: jaw worms, a small phylum of small marine animals (100 species). Hermaphrodite, live in muddy benthic habitat, scape food from particles with their jaw. A minor phylum.
- Chaetognatha: arrow worms. Only about 120 species, but huge numbers in the plankton; some are benthic. They are predators, up to 12 cm long. They use a neurotoxin to subdue prey. A minor phylum.
- Nematoda: the round worms. For purists, the name Nemata has priority. Despite their rather limited body form, this is a major phylum, with huge numbers in every conceivable habitat. Over 80,000 species have been described, and 15,000 are parasitic. It has been estimated that the total number may be several hundred thousand. A public relations claim that nematodes "account for 90% of all life at the bottom of the sea" has no reliable basis, but they are certainly important.
- Nematomorpha: small group of nematode-like parasites. They spend their larval stage in the body cavity of arthropods. The adult stage is free, but non-feeding, though it may live for several months. About 350 species. A minor phylum.
- Priapulida or Priapula: small phylum of 18 species, with large front section which can be drawn back into the body cavity and extruded for feeding. The larger species are carnivores, seizing prey. The Burgess Shale fauna from the Cambrian shows that the living species are but a remnant of a once much larger group.p358 A minor phylum.
- Kinorhyncha: another small phylum (150 species) with an introvert which carries a mouth at the end when extended. A minor phylum.
- Loricifera: a new phylum, discovered in the 1970s. They are microscopic, 100–485μm; ~100 species. They have an exoskeleton called a lorica, and an introvert which can be withdrawn into the trunk. They live at the bottom of the water column attached to gravel. Three species live completely without oxygen. A minor phylum.
- Xenoturbellida: a new phylum, by DNA sequence analysis. One genus with two species makes this a very minor phylum. It is basal among the deuterostomes.
- Acoelomorpha: a group once placed in the Platyhelminths, now DNA sequence analysis has it as a sister group to Xenoturbella, and basal to the deuterostomes. Also a minor phylum.
- Phoronida: A very small phylum, with 12 species. Live on the sea floor (benthic), build chitinous tubes covered with mud or sand or bore into calcareous rock. Usually have horeshoe-shaped lophophores with ciliated tentacles. A minor phylum.
- Brachiopoda: the lamp-shells, with a huge fossil record going back to the Cambrian. 12,000 species, of which 350 are still living (or 100 according to Clarkson).p158 They look rather like bivalves, and they do have an upper and lower part to the shell. However, their internal organisation is quite different.p395 They were the dominant inshore fauna (infauna) of the Palaeozoic, but were much reduced by the two main extinction events, the P/Tr and K/T. Bivalve molluscs took over their inshore habitats in the Mesozoic, and since then the brachiopods have been confined to deeper water, except for a handful of species.
- Echinodermata: One of the most important marine phyla, with radial symmetry. 17,000 living species, which all live in the ocean, mostly on the sea bed. This is the largest phylum which is entirely marine. The main classes are quite well-known. The Crinoids are 'sea lilies', a remnant of a once great clade; the Asterozoa are the starfish, major predators of shell-fish, and the brittle stars. The Echinozoa are the sea urchins, sand dollars and the sea cucumbers. There are also some extinct groups. The echinoderm fossil record is extensive. Larvae are varied and planktonic: pluteus (echinoids); dipleurula, then bipinneria; then brachiolaria (starfish); ophiopluteus (brittle stars); doliolaris (sea cucumbers).
- Hemichordata: The Chordates' closest relatives, three groups which are brought together in most modern taxonomies.
- Graptolites: fossil colonial animals.
- Pterobranchia: a small phylum of two or three marine groups which usually build tubes, and form small colonies on sea floor. They have a long fossil record. Zooids carry prominent ciliated tentacles. A minor phylum.
- Enteropneusta: the acorn worms. A small, well-defined group with 70 marine species. Relatives of the chordates. A minor phylum.
- Chordata: the phylum which contains the vertebrates. As with the Arthropoda, some taxonomists regard this as a Superphylum, with three phyla. Here, the chordata has three sub-phyla:
Depending on how one counts, the list contains 32 (or 39) phyla of metazoan animals. Of these, 20 are minor phyla, and at least 21 are exclusively aquatic, with several others in quasi-aquatic habitats on land. None are entirely terrestrial. This is testimony to the importance of water for life, and to the sea in particular. It is fairly certain that all phyla originated in the sea or, at any rate, in water. Most made their first showing in the Cambrian, or in the Ediacaran. Naturally, most of the soft-bodied phyla have left few fossils.
Phyla may be grouped according to evidence about their evolutionary relationships. The list above puts similar groups together, for example:
- Parazoa: all animals with different kinds of cells, but no tissues
- Eumetazoa: animals with different tissues (all except sponges)
This kind of megataxonomy is becoming more convincing as DNA sequence analysis proceeds through the phyla. Some entirely fossil groups are still placed where they are on anatomy and commonsense rather than hard molecular evidence. The trilobites are a good example. Their position in the Arthropoda is based on not much more than their bilateral symmetry and an exoskeleton. These groupings are discussed further in the references to this page.
- Arthur, Wallace 1997. The origin of animal body plans: a study in evolutionary developmental biology. Cambridge.
- Nielsen, Claus 2001. Animal evolution: interrelationships of the living phyla. 2nd ed, Oxford.
- Valentine, James W. 2004. On the origin of phyla. Chicago University Press.
- Cells of different types
- Barnes, Robert D. 1982. Invertebrate zoology. Holt-Saunders, Philadelphia PA. pp945–946. ISBN 0-03-056747-5.
- Counting creatures, Research highlights, Nature vol 465, 27 May 2010 p400.
- Millionths of a metre
- Clarkson E.N.K. 1998. Invertebrate palaeontology and evolution. 4th ed, Blackwell, Oxford.
- Rudwick M.J.S. 1970. Living and fossil brachiopods. Hutchinson, London.
- Fox, Richard; Barnes, Robert D. and Ruppert, Edward E. 2003. Invertebrate zoology: a functional evolutionary approach. Revision of Barnes' standard textbook. 1008 pages. ISBN 978-8131501047