dcsimg

Brief Summary

    Animal: Brief Summary
    provided by wikipedia

    Animals are multicellular eukaryotic organisms that form the biological kingdom Animalia. With few exceptions, animals consume organic material, breathe oxygen, are able to move, reproduce sexually, and grow from a hollow sphere of cells, the blastula, during embryonic development. Over 1.5 million living animal species have been described—of which around 1 million are insects—but it has been estimated there are over 7 million animal species in total. Animals range in length from 8.5 millionths of a metre to 33.6 metres (110 ft) and have complex interactions with each other and their environments, forming intricate food webs. The study of animals is called zoology.

    Most living animal species are in the Bilateria, a clade whose members have a bilaterally symmetric body plan. The Bilateria include the protostomes—in which many groups of invertebrates are found, such as nematodes, arthropods, and molluscs—and the deuterostomes, containing the echinoderms and chordates (including the vertebrates). Life forms interpreted as early animals were present in the Ediacaran biota of the late Precambrian. Many modern animal phyla became clearly established in the fossil record as marine species during the Cambrian explosion which began around 542 million years ago. 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived 650 million years ago.

    Aristotle divided animals into those with blood and those without. Carl Linnaeus created the first hierarchical biological classification for animals in 1758 with his Systema Naturae, which Jean-Baptiste Lamarck expanded into 14 phyla by 1809. In 1874, Ernst Haeckel divided the animal kingdom into the multicellular Metazoa (now synonymous with Animalia) and the Protozoa, single-celled organisms no longer considered animals. In modern times, the biological classification of animals relies on advanced techniques, such as molecular phylogenetics, which are effective at demonstrating the evolutionary relationships between animal taxa.

    Humans make use of many other animal species for food, including meat, milk, and eggs; for materials, such as leather and wool; as pets; and as working animals for power and transport. Dogs have been used in hunting, while many terrestrial and aquatic animals are hunted for sport. Non-human animals have appeared in art from the earliest times and are featured in mythology and religion.

    Brief Summary
    provided by EOL authors

    The Kingdom Animalia (=Metazoa) is one of a handful of lineages rooted far back in the branching "tree" that represents the history of life on Earth. This lineage that is composed of those organisms we know as "animals" represents one of the three major origins of multicellularity (the other two large and diverse groups of multicellular organisms are the fungi and the green plants).

    It is difficult to list characteristics that apply to all animals, since various branches of the animal tree have undergone a range of significant modifications. However, most animals obtain energy from other organisms. They generally feed on them as predators (killing and eating a prey item); parasites, including herbivores feeding on plants (feeding on their "prey" without killing it, at least not immediately); or detritivores (ingesting tiny bits of decomposing organic material such as fallen leaves). In contrast to animals, most plants make their own food, through the extraordinary process of photosynthesis, using energy captured from the sun; most fungi break down decaying organic material (without ingesting it) into its chemical constituents and absorb released nutrients. Animal cells lack a rigid cell wall (some form of which is typical of plants and most fungi) and their cell biology and physiology differ in a variety of ways from other organisms.

    The diversity of animals is impressive. Zhang (2011; 2013) recently coordinated an effort to outline a classification scheme for all known animals and to estimate species richness (i.e., number of species) in different parts of the animal tree. Results from this publication are enlightening. More than 1.5 million animal species have been described (and many more continue to be discovered and formally described each year). The phylum Arthropoda (insects, spiders, crustaceans, etc.) accounts for around 80% of this total; around 2/3 of the total is accounted for by the insects alone. Well over a third of all known insects (and around a quarter of all known animal species!) are beetles: nearly 400,000 different species of beetles have already been described. Among the known species of insects are also nearly 120,000 Hymenoptera (ants, bees, and wasps) and nearly 160,000 Lepidoptera (moths and butterflies). More than 40,000 spider species and over 50,000 species of Acari (mites and ticks) have been described. Nearly 70,000 species of Crustacea (crabs, shrimps, barnacles, pillbugs, and many groups completely unfamiliar to those who don't study them!) are known. The Myriapoda (millipedes, centipedes, and relatives) includes around 12,000 described species. The Mollusca (clams, snails, octopuses, and relatives) is among the largest of the animal phyla, with nearly 120,000 known species. There are over 17,000 known species of Annelida (segmented worms, including earthworms, "polychaete" worms, leeches, and their relatives), Even some groups most people have never even heard of are quite diverse. For example, there are over 1000 described Acanthocephala, over 3000 Pseudoscorpiones, and more than 1500 Rotifera species (and rotifer specialists believe this last number may represent just a tenth or less of the true global rotifer species diversity). By comparison with these invertebrate clades, the generally more familiar vertebrate groups are less diverse, but many people may still be surprised to learn, for example, that there are around 32,000 species of described "fishes" and nearly 6,000 described mammal species. The numbers presented here are merely an appetizer. Anyone seriously interested in biodiversity will thoroughly enjoy studying the original volume by Zhang and colleagues which is freely available online.

Comprehensive Description

Education Resources

Citizen Science links