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Phylum in the animal kingdom Chordata (chordate), animals having at least at some stage of development a notochord, dorsally situated central nervous system, and gill clefts; includes mammals, birds, reptiles, amphibians, fish, and certain marine lower forms (such as lancelets, sea squirts, and tunicates); includes some 45,000 living species. Hemichordata (hemichordate), a phylum in the kingdom Animalia that contains a group of ancestral marine animals, including the classes Enteropneusta, Pterobranchia, and Graptolithina, that have in the proboscis an outgrowth of the pharyngeal wall which superficially resembles the notochord of the chordates; includes some 230 living species. Echinodermata (echinoderms), a phylum of usually radially symmetrical marine animals with a calcareous exoskeleton, they are slow moving and rely mainly on small processes called tube feet for locomotion. All are marine, including starfish, sea urchins, sea lilies, and sea cucumbers; includes some 6,000 living species. Chaetognatha (Chaetognath), a phylum of torpedo-shaped planktonic wormlike marine organisms (arrowworms) having curved bristles on either side of the head for seizing their prey, usually small crustacea; includes some 50 living species. Brachiopoda (lampshells), a phylum of marine animals characterized by a bivalve shell and by a pair of cilia-covered arms by which a current of water is made to bring microscopic food to the mouth; includes some 250 living species and 30,000 fossil species. Loricifera (loriciferans), a phylum of minute sediment dwelling marine aschelminths only 0.5 mm (0.02 in) long that adhere tightly to gravel substrates. Kinorhyncha or Echinodera (kinorhynchs), a phylum or class of free-living, segmented, marine worms with spiny bodies that live in subtidal mud and feed principally on diatoms; includes some 100 living species. Bryozoa or Ectoprocta (bryzoans), a phylum of minute, mosslike marine and freshwater creatures, with distinct alimentary canals, they usually form permanently attached branched or mossy colonies and reproduce by budding; includes some 4,000 living species. Phoronida (horseshoe worms), a small phylum of small, wormlike marine animals, having tentacles around the mouth, that live in a chitinous tube with the lophophore and anus at the open end. All are marine and inhabit shallow coastal waters; includes some 10 living species. Pentastomida or Linguatulida (tongue worms), a small phylum of wormlike segmented animals, having no circulatory, respiratory, or excretory systems. They are parasites in the respiratory system of some vertebrates including snakes, crocodiles, and some mammals and birds; includes some 90 living species. Tardigrada (water bears), a class or subphylum of minute arthropods having sucking mouthparts and four pairs of stout clawed legs, usually living in water or damp moss. They are able to survive dehydration and are distributed from sea floors to fresh water creeks to roadside ditches; includes some 400 living species. Priapula (priapulida), a small phylum of free-living marine worms that are cylindrical and ringed, having spiny and wartlike appendages on the proboscis, abdomen, and tail; includes some 17 living species. Echiura (spoon worms), any of a taxon (class Echiuroidea) of marine worms of uncertain taxonomic similarities which have a sensitive but nonretractile proboscis above the mouth, they live in sand burrows or rock crevices; includes some 17 living species. Sipuncula (peanut worms), a phylum of marine worms having a saclike body and a long proboscis, they inhabit marine substrates, burrowing in sand, mud, or tropical reef limestone; includes some 300 living species. Pogonophora (beard worms), a phylum of marine wormlike animals of uncertain systematic relationships that live in chitinous tubes, have obscure segmentation and a beardlike bunch of tentacles used in respiration and feeding. Beard worms lack a mouth and digestive tract; includes some 80 living species. Arthropoda (arthropods), the largest phylum of invertebrate animals including insects, arachnids, and crustaceans that have a segmented body and jointed appendages, typically with paired, jointed antennae, wings, or legs, a usually chitinous exoskeleton molted at intervals and a dorsal anterior brain connected to a ventral chain of ganglia; includes one million living species. Annelida (segmented worms), a phylum of usually elongated segmented worms that have a true coelom. Invertebrates such as earthworms, various marine worms, and leeches are included. Often found with a pair of bristlelike projections (setae) on each segment used in crawling, they also have a closed vascular system with hemoglobin-bearing blood; includes some 8,700 living species. Mollusca (mollusks), the second largest animal phylum including oysters, snails, clams and squid. Mollusks typically are soft-bodied animals, most with a calcium carbonate shell secreted by the mantle, a muscular foot for locomotion, and gills. Other forms, such as the octopus and squid, can grow to considerable size; includes some 100,000 living species. Gnathostomulida (jaw worms), tiny worms that live in marine sand. The phyla was first discovered in 1956; includes 80 living species. Acanthocephala (spiny-headed worms), a phylum of spiny-headed unsegmented endoparastic worms with a reversible, elongated proboscis bearing hooks by which attachment is made to the intestinal wall of the host. The juveniles develop within crustaceans and insects, and adults are parasitic in the digestive tracts of vertebrates; includes 500 living species. Nematomorpha (hairworms), a small phylum of pseudocoelomate wormlike animals which are parasitic on arthropods as juveniles but free-living as adults; includes 230 living species. Nematoda (roundworms or nematodes), a phylum of elongated cylindrical, smooth-skinned, unsegmented worms, both aquatic and terrestrial, parasitic in animals or plants or free-living in soil or water; includes some 10,000 living species. Rotifera (rotifers or "wheel animals"), in the phylum Aschelminthes, a class of chiefly freshwater aquatic invertebrates, wormlike or spherical in appearance. They are minute, often microscopic, but many-celled, the corona of cilia by which they move and feed gives the appearance of a revolving wheel; includes some 1,800 living species. Gastrotricha (Gastrotrichs), a phylum of minute marine and freshwater pseudocoelomate animals that usually have a spiny or scaly cuticle and cilia on the ventral surface; includes some 400 living species. Nemertinea or Rhynchocoela (proboscis worms), a phylum of often elongate, vividly colored marine worms most of which burrow in the mud or sand along seacoasts. Also called the ribbon worm, prey is taken with an extensible proboscis; includes some 650 living species. Platyhelminthes (flatworms), the phylum of soft-bodied flatworms such as the planarians, the parasitic flukes, and tapeworms, also included are the free-living class Turbellaria, these worms lack respiratory and circulatory systems, their flat design allows for gas and nutrient exchange from their environment; includes some 13,000 living species. Ctenophora (comb jellies), a phylum containing the comb jellies, gelatinous marine organisms, superficially resembling jellyfishes, swimming by means of eight meridional bands of locomotory cilia; includes 50 living species. Cnidaria (true jellyfish and hydroids, corals, and sea anemones), including jellyfish, coral and hydras. Animals with a life history which includes an attached polyp stage as in sea anemones, a free-swimming medusa as in jellyfish, or both. Typically prey is taken with stinging tentacles. They are saltwater animals, except for a few freshwater forms such as the hydra; includes 9,000 living species. Porifera (sponges), the phylum of sponges, the most primitive of all multicellular organisms, having no true tissues or organs. They live attached to a substrate and feed by drawing water into the body through pores, then filtering food particles with flagellated cells. All are sessile, most are marine, but a few occur in freshwater; includes 5,000 living species. Placozoa, a phylum of Metazoa containing two species of small (2-3 mm), flattened, ameoba-like marine organisms with a flattened body composed of two outer layers of flagellated epithelioid cells enclosing loose cells. The body lacks symmetry, has no organs, and has no muscular or nervous system; they feed on algae and protozoans by extracellular predigestion. |