Segmentation (biology)Segmentation in biology is the division of some animal and plant body plans into a series of repetitive segments. This article focuses on the segmentation of animal body plans, specifically using the examples of the taxa Arthropoda, Chordata, and Annelida. These three groups form segments by using a "growth zone" to direct and define the segments. While all three have a generally segmented body plan and use a growth zone, they use different mechanisms for generating this patterning.
OpabiniaOpabinia regalis is an extinct, stem group arthropod found in the Middle Cambrian Burgess Shale Lagerstätte (505 million years ago) of British Columbia. Opabinia was a soft-bodied animal, measuring up to 7 cm in body length, and its segmented trunk had flaps along the sides and a fan-shaped tail. The head shows unusual features: five eyes, a mouth under the head and facing backwards, and a clawed proboscis that probably passed food to the mouth. Opabinia probably lived on the seafloor, using the proboscis to seek out small, soft food.
OnychophoraOnychophora Qnᵻ'kQf@r@ (from ονυχής, onyches, "claws"; and φέρειν, pherein, "to carry"), commonly known as velvet worms (due to their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus pəˈrɪpətəs (after the first described genus, Peripatus), is a phylum of elongate, soft-bodied, many-legged panarthropods. In appearance they have variously been compared to worms with legs, caterpillars, and slugs. They prey upon other invertebrates, which they catch by ejecting an adhesive slime.
Brine shrimpArtemia is a genus of aquatic crustaceans also known as brine shrimp. It is the only genus in the family Artemiidae. The first historical record of the existence of Artemia dates back to the first half of the 10th century AD from Lake Urmia, Iran, with an example called by an Iranian geographer an "aquatic dog", although the first unambiguous record is the report and drawings made by Schlösser in 1757 of animals from Lymington, England. Artemia populations are found worldwide, typically in inland saltwater lakes, but occasionally in oceans.
SpringtailSpringtails (Collembola) form the largest of the three lineages of modern hexapods that are no longer considered insects (the other two are the Protura and Diplura). Although the three orders are sometimes grouped together in a class called Entognatha because they have internal mouthparts, they do not appear to be any more closely related to one another than they are to all insects, which have external mouthparts. Collembolans are omnivorous, free-living organisms that prefer moist conditions.
ExtremophileAn extremophile (from Latin extremus meaning "extreme" and Greek philiā (φιλία) meaning "love") is an organism that is able to live (or in some cases thrive) in extreme environments, i.e. environments with conditions approaching or expanding the limits of what known life can adapt to, such as extreme temperature, radiation, salinity, or pH level. Since the definition of an extreme environment is relative to an arbitrarily defined standard, often an anthropocentric one, these organisms can be considered ecologically dominant in the evolutionary history of the planet.
CuticleA cuticle (ˈkjuːtɪkəl), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non-homologous, differing in their origin, structure, function, and chemical composition. In human anatomy, "cuticle" can refer to several structures, but it is used in general parlance, and even by medical professionals, to refer to the thickened layer of skin surrounding fingernails and toenails (the eponychium), and to refer to the superficial layer of overlapping cells covering the hair shaft (cuticula pili), consisting of dead cells, that locks the hair into its follicle.
Deinococcus radioduransDeinococcus radiodurans is an extremophilic bacterium and one of the most radiation-resistant organisms known. It can survive cold, dehydration, vacuum, and acid, and therefore is known as a polyextremophile. It has been listed as the world's toughest known bacterium in The Guinness Book Of World Records. The name Deinococcus radiodurans derives from the Ancient Greek δεινός () and κόκκος () meaning "terrible grain/berry" and the Latin radius and durare, meaning "radiation surviving".
