Bilateria

• Overview
• Taxonomy
• Phyla
• References
• Footnotes
• Sources

Overview

Taxonomy

The Subkingdom Bilateria is further organized into finer groupings including:

• Branch (2): Deuterostomia · Protostomia
• Infrakingdom (8): Chordonia · Coelenterata · Coelomopora · Ecdysozoa · Lophotrochozoa · Platyzoa · Rhizaria · Spongiaria
• Superphylum (5): Aschelminthes · Eutrochozoa · Gnathifera · Lophophorata · Panarthropoda
• Phylum (31): Acanthocephala · Acoelomorpha · Annelida · Arthropoda · Brachiopoda · Bryozoa · Chaetognatha · Chordata · Cycliophora · Dicyemida · Echinodermata · Echiura · Entoprocta · Gastrotricha · Gnathostomulida · Hemichordata · Kinorhyncha · Loricifera · Mollusca · Nematoda · Nematomorpha · Nemertea · Onychophora · Orthonectida · Platyhelminthes · Priapulida · Rotifera · Sipuncula · Tardigrada · Vetulicolia · Xenoturbellida

Phyla

Acanthocephala

Acanthocephala (Greek , akanthos, thorn + ?efa??, kephale, head) is a phylum of parasitic worms known as acanthocephales, thorny-headed worms, or spiny-headed worms, characterized by the presence of an evertable proboscis, armed with spines, which it uses to pierce and hold the gut wall of its host. Acanthocephalans typically have complex life cycles, involving a number of hosts, including invertebrates, fishes, amphibians, birds, and mammals. About 1150 species have been described.^{[citation needed]} [more]

Acoelomorpha

[more]

Annelida

The annelids (also called "ringed worms"), formally called Annelida (from French annel?s "ringed ones", ultimately from Latin anellus "little ring"), are a large phylum of segmented worms, with over 17,000 modern species including ragworms, earthworms and leeches. They are found in marine environments from tidal zones to hydrothermal vents, in freshwater, and in moist terrestrial environments. Although most textbooks still use the traditional division into polychaetes (almost all marine), oligochaetes (which include earthworms) and leech-like species, research since 1997 has radically changed this scheme, viewing leeches as a sub-group of oligochaetes and oligochaetes as a sub-group of polychaetes. In addition, the Pogonophora, Echiura and Sipuncula, previously regarded as separate phyla, are now regarded as sub-groups of polychaetes. Annelids are considered members of the Lophotrochozoa, a "super-phylum" of protostomes that also includes molluscs, brachiopods, flatworms and nemerteans. [more]

Arthropoda

An arthropod is an invertebrate animal having an exoskeleton (external skeleton), a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda (from Greek ?rthron, "joint", and p?d?? pod?s "foot", which together mean "jointed feet"), and include the insects, arachnids, crustaceans, and others. Arthropods are characterized by their jointed limbs and cuticles, which are mainly made of a-chitin; the cuticles of crustaceans are also biomineralized with calcium carbonate. The rigid cuticle inhibits growth, so arthropods replace it periodically by molting. The arthropod body plan consists of repeated segments, each with a pair of appendages. It is so versatile that they have been compared to Swiss Army knives, and it has enabled them to become the most species-rich members of all ecological guilds in most environments. They have over a million described species, making up more than 80% of all described living animal species, and are one of only two animal groups that are very successful in dry environments ? the other being the amniotes. They range in size from microscopic plankton up to forms a few meters long. [more]

Brachiopoda

Brachiopods, phylum Brachiopoda, are marine animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection. Two major groups are recognized, articulate and inarticulate. Articulate brachiopods have toothed hinges and simple opening and closing muscles, while inarticulate brachiopods have untoothed hinges and a more complex system of muscles used to keep the two halves aligned. In a typical brachiopod a stalk-like pedicle projects from an opening in one of the valves, known as the pedicle valve, attaching the animal to the seabed but clear of silt that would obstruct the opening. [more]

Bryozoa

The Bryozoa, also known as Ectoprocta or commonly as moss animals^[], are a phylum of aquatic invertebrate animals. Typically about 0.5 millimetres (0.020 in) long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia. Most marine species live in tropical waters, but a few occur in oceanic trenches, and others are found in polar waters. One class lives only in a variety of freshwater environments, and a few members of a mostly marine class prefer brackish water. Over 4,000 living species are known. One genus is solitary and the rest colonial. [more]

Chaetognatha

Chaetognatha, meaning hair-jaws, and commonly known as arrow worms, are a phylum of predatory marine worms that are a major component of plankton worldwide. About 20% of the known species are benthic, that is belonging to the lowest zone of the ocean, or benthic zone, and can attach to algae and rocks. They are found in all marine waters, from surface tropical waters and shallow tide pools to the deep sea and polar regions. Most chaetognaths are transparent and are torpedo shaped, but some deep-sea species are orange. They range in size from 2 to 120 millimetres (0.079 to 4.7 in). [more]

Chordata

Chordates (phylum Chordata) are animals which are either vertebrates or one of several closely related invertebrates. They are united by having, for at least some period of their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail. The phylum Chordata consists of three subphyla: Tunicata, represented by tunicates; Cephalochordata, represented by lancelets; and Craniata, which includes Vertebrata. The Hemichordata have been presented as a fourth chordate subphylum, but they are now usually treated as a separate phylum. Tunicate larvae have both a notochord and a nerve cord which are lost in adulthood. Cephalochordates have a notochord and a nerve cord (but no brain or specialist sensory organs) and a very simple circulatory system. Craniates are the only sub-phylum whose members have skulls. In all craniates except for hagfish, the dorsal hollow nerve cord is surrounded with cartilaginous or bony vertebrae and the notochord is generally reduced; hence, hagfish are not regarded as vertebrates. The chordates and three sister phyla, the Hemichordata, the Echinodermata and the Xenoturbellida, make up the deuterostomes, one of the two superphyla that encompass all fairly complex animals. [more]

Cycliophora

Symbion is the name of a genus of aquatic animals, less than ? mm wide, found living attached to the bodies of cold-water lobsters. They have sac-like bodies, and three distinctly different forms in different parts of their two-stage life-cycle. They appear so different from other animals that they were assigned their own, new phylum Cycliophora shortly after they were discovered in 1995. This was the first new phylum of multicelled organism to be discovered since the Loricifera in 1983. [more]

Dicyemida

[more]

Echinodermata

Echinoderms (Phylum Echinodermata) are a phylum of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone. Aside from the hard-to-classify Arkarua, the first definitive members of the phylum appeared near the start of the Cambrian period. [more]

Echiura

The Echiura, or spoon worms, are a small group of marine animals. They are often considered to be a group of annelids, although they lack the segmented structure found in other members of that group, and so may also be treated as a separate phylum. However, phylogenetic analyses of DNA sequences place echiurans and pogonophorans within the Annelida. The Echiura fossilise poorly and the earliest known specimen is from the Upper Carboniferous (called the Pennsylvanian in North America). However, U-shaped fossil burrows that could be Echiuran have been found dating back to the Cambrian. [more]

Entoprocta

Entoprocta, whose name means "anus inside", is a phylum of mostly sessile aquatic animals, ranging from 0.1 to 7 millimetres (0.0039 to 0.28 in) long. Mature individuals are goblet-shaped, on relatively long stalks. They have a "crown" of solid tentacles whose cilia generate water currents that draw food particles towards the mouth, and both the mouth and anus lie inside the "crown". The superficially similar Bryozoa (Ectoprocta) have the anus outside a "crown" of hollow tentacles. Most families of entoprocts are colonial, and all but 2 of the 150 species are marine. A few solitary species can move slowly. [more]

Gastrotricha

The gastrotrichs (from Greek ?ast??, gaster ["stomach"], and ????, thrix ["hair"]), often called hairy backs, are a phylum of microscopic (0.06-3.0 mm) animals abundant in fresh water and marine environments. Most fresh water species are part of the periphyton and benthos. Marine species are found mostly interstitially in between sediment particles, while terrestrial species live in the water films around grains of soil. [more]

Gnathostomulida

Gnathostomulids, or jaw worms, are a small phylum of nearly microscopic marine animals. They inhabit sand and mud beneath shallow coastal waters and can survive in relatively anoxic environments. They were first recognised and described in 1956. [more]

Hemichordata

Hemichordata is a phylum of marine deuterostome animals, generally considered the sister group of the echinoderms. They date back to the Lower or Middle Cambrian and include two main classes: Enteropneusta (acorn worms), and Pterobranchia. A third class, Planctosphaeroidea, is known only from the larva of a single species. The extinct class Graptolithina is closely related to the pterobranchs. [more]

Kinorhyncha

Kinorhyncha (Gr. ?????, kineo 'move' + ??????, rhynchos 'snout') is a phylum of small (1 mm or less) marine pseudocoelomate invertebrates that are widespread in mud or sand at all depths as part of the meiobenthos. They are also called mud dragons. [more]

Loricifera

[more]

Mollusca

The Mollusca (pronounced ), common name molluscs or mollusks (pronounced /'m?l?sks/), is a large phylum of invertebrate animals. There are around 85,000 recognized extant species of molluscs. Mollusca is the largest marine phylum, comprising about 23% of all the named marine organisms. Numerous molluscs also live in freshwater and terrestrial habitats. Molluscs are highly diverse, not only in size and in anatomical structure, but also in behaviour and in habitat. The phylum is typically divided into nine or ten taxonomic classes, of which two are entirely extinct. Cephalopod molluscs such as squid, cuttlefish and octopus are among the most neurologically advanced of all invertebrates ? and either the giant squid or the colossal squid is the largest known invertebrate species. The gastropods (snails and slugs) are by far the most numerous molluscs in terms of classified species, and account for 80% of the total. [more]

Nematoda

The nematodes () or roundworms (phylum Nematoda) are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. The total number of nematode species has been estimated to be about 1,000,000. Unlike cnidarians or flatworms, roundworms have tubular digestive systems with openings at both ends. [more]

Nematomorpha

Nematomorpha (sometimes called Gordiacea, and commonly known as horsehair worms or Gordian worms) is a phylum of parasitic animals that are superficially morphologically similar to nematode worms, hence the name. They range in size in most species from 50 to 100 centimetres (20 to 39 in) long and can reach in extreme cases up to 2 metres, and 1 to 3 millimetres (0.039 to 0.12 in) in diameter. Horsehair worms can be discovered in damp areas such as watering troughs, streams, puddles, and cisterns. The adult worms are free living, but the larvae are parasitic on beetles, cockroaches, orthopterans, and crustaceans. About 351 species are known and a conservative estimate suggests that there may be about 2000 species worldwide. The name "Gordian" stems from the legendary Gordian knot. This relates to the fact that nematomorpha often tie themselves in knots. [more]

Nemertea

Nemertea is a phylum of invertebrate animals also known as "ribbon worms" or "proboscis worms". Alternative names for the phylum have included Nemertini, Nemertinea and Rhynchocoela. Although most are less than 20 centimetres (7.9 in) long, one specimen has been estimated at 54 metres (177 ft), which would make it the longest animal ever found. Most are very slim, usually only a few millimeters wide, although a few have relatively short but wide bodies. Many have patterns of yellow, orange, red and green coloration. [more]

Onychophora

The velvet worms (Onychophora ? literally "claw bearers", also known as Protracheata) are a minor ecdysozoan phylum. These obscurely segmented organisms have tiny eyes, antennae, multiple pairs of legs and slime glands. They have variously been compared to worms with legs, caterpillars and slugs. Most common in tropical regions of the Southern Hemisphere, they prey on smaller animals such as insects, which they catch by squirting an adhesive slime. In modern zoology, they are particularly renowned for their curious mating behaviour and for bearing live young. They are becoming increasingly popular as pets due to their bizarre appearance and eating habits.^[] [more]