Animalia  

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.

La rata canguro orejona tiene las orejas más grandes de todas las ratas canguro y como pesa alrededor de 85 gramos califica como una de las más grandes en California dentro de la especie Dipodomys. Es de color canela obscura con las partes ocultas blancas y orejas color café. Vive únicamente en la parte sur de la Región del Gavilán en los condados de San Benito y Monterrey en California. A causa de los incendios forestales en el chaparral adonde ella vive y debido a la sobrepoblación humana en ese hábitat, la rata canguro orejona está catalogada como rara en la Unión Internacional para la Conservación de la Naturaleza y Recursos Naturales (UICN). Los depredadores incluyen a búhos, zorros y coyotes.

Enlaces:
Especies de Mamíferos del Mundo
Pulse aquí para el índice sobre especies de mamíferos de: The American Society of Mammalogists

El mapa muestra la posible distribución del lobo rojo cuando los primeros inmigrantes europeos llegaron a norteamérica. En los siglos siguientes, los lobos rojos fueron llevados casi a la extinción, los coyotes regresaron a su distribución original y muchas veces las dos especies se cruzaron. La pequeña población de lobos rojos que existe en la actualidad en estado silvestre, es el resultado de animales que fueron criados en cautiverio y reintroducidos. En 1997, biólogos contaron cerca de 80 lobos rojos en dos localidades diferentes. Además, había entonces 160 animales en cautiverio. En su ambiente natural, viven en manadas, cazan principalmente durante la noche aunque pueden entrar en actividad durante el día en el invierno. Sólo usan madrigueras para criar a sus cachorros.

Enlaces:
Especies de Mamíferos del Mundo
Pulse aquí para el índice sobre especies de mamíferos de: The American Society of Mammalogists

The Animalia are the animals. The word metazoa is also used for this group. Animals include sponges, cnidaria and all animals with epithelia (sheets of cells covering the outside of the organism, the gut system, and from which other organisms are derived). Animals are distinguished as organisms which may be multicellular, use extracellular collagen as a skeletal material, have a sexual developmental cycle that involves motile sperm, relatively immotile eggs, and development that involves the formation of a blastula (or are derived from organisms with these features). With our current understanding, this life form has diversified much more than any other group. Animals were often divided into the vertebrates (including fish, amphibia, reptiles and birds, and mammals), and the invertebrates. Most invertebrates and all vertebrates are organisms that are bilaterally symmetrical - with many organs such as appendages motion, sensory organs, nerves and muscle - similar on both sides of the body. Most animals have a head - a region with a concentration of sensory organisms and nervous system (brain). The animals evolved from a group of unicellular organisms - the choanoflagellates or collar flagellates. The first multicellular organisms were the sponges. Later organisms like jellyfish appeared, and these are represented in the fossil record. While sponges are filter feeders, the cnidaria (includes jellyfish) eat larger morsels of food. This style of feeding, coupled with the ability to actively move, set off the explosion of animal life. Worm-like organisms with appendages, heads, centralized nervous systems followed next and much of the animal diversity was established in the Cambrian geological period. Animals are the most successful (in terms of number of species) of evolutionary lineages that moved from unicellularity to multicelluarity - current estimates being that there are about 1,500,000 species, but this excludes fossil species and the myriads of so far undescribed animals.