Animals are multicellular, eukaryotic organisms of the kingdom Animalia (also called Metazoa). Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their lives. Most animals are motile, meaning they can move spontaneously and independently. All animals must ingest other organisms or their products for sustenance.
Most known animal phyla appeared in the fossil record as marine species during the Cambrian explosion, about 542 million years ago. Animals are divided into various sub-groups, some of which are: vertebrates (birds, mammals, amphibians, reptiles, fish); mollusks (clams, oysters, octopuses, squid, snails); arthropods (millipedes, centipedes, insects, spiders, scorpions, crabs, lobsters, shrimp); annelids (earthworms, leeches); sponges; and jellyfish.
Selected article of the month
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. Some species eject unfertilized ova into the water while others keep their ova in brood chambers until they hatch, and some of these species use placenta-like organs to nourish the developing eggs. After hatching, the larvae swim for a short time and then settle on a surface. There they metamorphose, and the larval gut generally rotates by up to 180°, so that the mouth and anus face upwards. Both colonial and solitary species also reproduce by cloning – solitary species grow clones in the space between the tentacles and then release them when developed, while colonial ones produce new members from the stalks or from corridor-like stolons.
Some species of nudibranchs ("sea slugs") and turbellarian flatworms prey on entoprocts. A few entoproct species have been found living in close association with other animals. It is uncertain whether any are invasive species.
Selected animal of the month
Sydney funnel-web spider
The Sydney funnel-web spider Atrax robustus
, is an Australian funnel-web spider usually found within a 100 km (62 mi) radius of Sydney
, New South Wales
Sydney funnel-webs are medium-to-large in size, with a body length ranging from 2 cm to 7 cm (0.9" to 3"). They are glossy and darkly coloured, ranging from blue-black to black to brown or dark-plum coloured. The carapace covering the cephalothorax is almost hairless and so appears smooth and glossy. The shorter lived males are smaller than females but longer legged. It is one of three species of the genus Atrax in the family Hexathelidae. The common name of the species is shared by other members of the genus Hadronyche, but it and the northern tree funnel-web are the only Australian funnel-web spiders known to have inflicted fatal bites to humans.
Selected quote of the month
When the fox dies, fowls do not mourn.
In biology, a phylum is a taxonomic rank below Kingdom and above Class. "Phylum" is equivalent to the botanical term division. The kingdom Animalia contains approximately forty phyla; the kingdom Plantae contains twelve divisions. Current research in phylogenetics is uncovering the relationships between phyla, which are contained in larger clades, like Ecdysozoa and Embryophyta. The best known animal phyla are the Mollusca, Porifera, Cnidaria, Platyhelminthes, Nematoda, Annelida, Arthropoda, Echinodermata, and Chordata, the phylum to which humans belong, along with all other vertebrate species. Although there are 36 animal phyla, these nine include over 96% of animal species. Many phyla are exclusively marine, and only one phylum, the Onychophora (velvet worms) is entirely absent from the world's oceans—although ancestral onycophorans were marine.