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An optical instrument that permits viewing along a displaced or deflected axis, providing an observer with the view from a position which may be inaccessible or dangerous. Periscopes range in complexity from the simple unit-power tank periscope to the complex multielement submarine periscope.
Industry:Science
An optical manifestation of a large-scale electrical discharge process which surrounds the Earth. The discharge is powered by the so-called solar wind–magnetosphere generator. The Sun continuously blows out its upper atmosphere, the corona, with a supersonic speed. This fully ionized and magnetized gas flow interacts with the Earth's magnetic field, resulting in a comet-shaped cavity (the magnetosphere) carved around the Earth, while the lines of force of the Earth's magnetic field and of the solar wind magnetic field interconnect. Electric power of as much as 10<sup>12</sup> W is generated as the solar wind blows across the interconnected field lines near the comet-shaped boundary. A part of the electric current (carried mainly by electrons) thus generated flows between the magnetospheric boundary and an annular, ring-shaped region of the polar upper atmosphere along the lines of force of the Earth's magnetic field.
Industry:Science
An order (or a class according to some taxonomists) of the Acanthocephala characterized by the presence of a small number of giant subcuticular nuclei which are similar to the embryonic nuclei. Body spines may or may not be present and the chief lacunar vessels are dorsal and lateral. The cement gland of the male is a single syncytial organ with a specialized cement reservoir. Ligament sacs persist in the female. Proboscis hooks are few in number and arranged in circles. Eggs are ellipsoidal and thin shelled. These worms are parasitic in cold-blooded vertebrates (turtles, fish). The cystacanth occurs in crustaceans.
Industry:Science
An order (or class, according to some classifications) of the phylum Acanthocephala. The adult worms are parasitic in terrestrial vertebrates. The body wall and lemnisci of species in this order have numerous amitotically fragmented nuclei or a few ameboid giant nuclei. The main trunks of the lacunar system are dorsal and ventral, or dorsal. Typically, there are eight separate cement glands in the male. Two ligament sacs are present in the female, one dorsal, the other ventral. They are persistent and united with the openings of the uterine bell. The eggs are elliptical and have a thick shell. The proboscis receptacle has a conspicuous ventral cleft or is a closed sac with two concentric muscle layers. The proboscis hooks occur in long rows or spiral rows, and the trunk lacks spines. The cystacanth occurs in grubs, roaches, and grasshoppers. Some common archiacanthocephalans are <i>Oncicola canis</i>, <i>Moniliformis moniliformis</i>, and <i>Macracanthorhynchus hirudinaceus</i>.
Industry:Science
An order (xiphosurids, or horseshoe crabs) of the class Xiphosura (phylum Arthropoda). These “sword-tailed” arthropods are a classic example of a “living fossils” group that has seemingly changed little over a period of many millions of years.
Industry:Science
An order and clade of elongate lepospondyls with highly reduced limbs and a lightly built, open skull known from the Middle Pennsylvanian to Lower Permian (305–270 million years ago) of North America and the British Isles. Unlike other lepospondyls, no lysorophians have been found in continental Europe. The vast majority of specimens come from two localities: the coal deposits of Linton, Ohio, and the Clear Fork redbeds of north central Texas. They were aquatic in their lifestyle, and are frequently found in large numbers curled in burrows. These burrows are believed to be estivation chambers, structures constructed by animals for periods of dormancy associated with suboptimal living conditions.
Industry:Science
An order comprising the even-toed ungulates (hoofed mammals). There are two main radiations: the predominantly omnivorous Bunodontia, including suoids (such as pigs, peccaries, and hippos); and the more herbivorous Selenodontia, including camels and ruminants (such as deer, giraffe, cattle, sheep, and antelope). Artiodactyla contains about 213 living species, making it the fifth most speciose order of mammals (exceeded primarily by rodents and bats, and slightly by carnivores and primates). First known from the early Eocene, artiodactyls have proliferated during the last 55 million years to reach great diversity (especially among the family Bovidae). Their radiation is often contrasted with that of the odd-toed ungulates, or Perissodactyla (horses, rhinos, and tapirs). Artiodactyls are also important for human economy and agriculture, comprising most of the domestic animals, providing milk, wool, and most of the meat supply. See also: Perissodactyla
Industry:Science
An order containing seven superfamilies of marine and brackish bivalves with byssal attachment at some time in their geological history (the Ostreacea are exceptional, with the lower valve attached by byssal cement at settlement, and with no record of ancestral attachment by byssal threads). Byssal attachment is associated with departure from the ancestral isomyarian form; Mytilacea and Pinnacea are heteromyarian, with a small anterior adductor muscle; others are monomyarian, with one central posterior adductor. Byssal attachment is lost in some: <i>Placuna</i> is free-living; <i>Pecten maximus</i> can right itself if inverted; <i>Chlamys</i> can swim to escape from starfish; some <i>Lima</i> can swim, while the tropical <i>Amusium</i> swims strongly. Pearls are obtained from <i>Pinctada</i> (Pteriacea).
Industry:Science
An order formerly in Osteoglossiformes but now independent, with the two orders comprising the extant Osteoglossomorpha, a primitive group of teleost fishes. The Hiodontiformes consist of one family, one genus, and two extant species, <i>Hiodon alosoides</i> (goldeye) and <i>H. tergisus</i> (mooneye). Hiodontids superficially resemble clupeids and for many years were classified as clupeiforms. The body is deep and laterally compressed and has a ventral keel, but the keel is not serrated as in most clupeids; the eyes are far forward and large, with the diameter greater than the length of the snout; the scales are large and cycloid and either bright silvery or golden; the anal fin base is much longer than the dorsal fin base; and the caudal fin is forked. The goldeye differs from the mooneye in having 9 or 10 principal dorsal fin rays versus 11 or 12, and a ventral keel extending anteriorly past the pelvic fins versus not extending anteriorly past the pelvic fins.
Industry:Science
An order in the class Actinopterygii, subdivision Euteleostei, superorder Acanthopterygii. The Mugiliformes comprise 17 genera and about 72 species, all in the single family Mugilidae, the mullets (also known as grey mullets). Past classifications considered mullets as primitive perciforms; however, they are presently deemed subperciforms and are the only order in Mugilomorpha, one of three series making up the Acanthopterygii.
Industry:Science
