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Spiny Dogfish
The spiny dogfish (''Squalus acanthias''), spurdog, mud shark, or piked dogfish is one of the best known species of the Squalidae (dogfish) family of sharks, which is part of the Squaliformes order. While these common names may apply to several species, ''Squalus acanthias'' is distinguished by two spines (one anterior to each dorsal fin) and no anal fin. It lives in shallow waters and further offshore in most parts of the world, especially in temperate waters. Those in the northern Pacific Ocean were reevaluated in 2010 and found to constitute a separate species, now called the Pacific spiny dogfish (''Squalus suckleyi''). Description and behaviour The spiny dogfish has dorsal fins, no anal fin, and white spots along its back. The caudal fin has asymmetrical lobes, forming a heterocercal tail. The species name ''acanthias'' refers to the shark's two spines. These are used defensively. If captured, the shark can arch its back to pierce its captor with spines near the dorsal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tortonian
The Tortonian is in the geologic time scale an age or stage of the late Miocene that spans the time between 11.608 ± 0.005 Ma and 7.246 ± 0.005 Ma (million years ago). It follows the Serravallian and is followed by the Messinian. The Tortonian roughly overlaps with the regional Pannonian Stage of the Paratethys timescale of Central Europe. It also overlaps the upper Astaracian, Vallesian and lower Turolian European land mammal ages, the upper Clarendonian and lower Hemphillian North American land mammal ages and the upper Chasicoan and lower Huayquerian South American land mammal ages. Definition The Tortonian was introduced by Swiss stratigrapher Karl Mayer-Eymar in 1858. It was named after the Italian city of Tortona in the Piedmont region. The base of the Tortonian Stage is at the last common appearance of calcareous nanoplankton '' Discoaster kugleri'' and planktonic foram '' Globigerinoides subquadratus''. It is also associated with the short normal pol ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ovoviviparity
Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop inside eggs that remain in the mother's body until they are ready to hatch. The young of some ovoviviparous amphibians, such as '' Limnonectes larvaepartus'', are born as larvae, and undergo further metamorphosis outside the body of the mother. Members of genera '' Nectophrynoides'' and '' Eleutherodactylus'' bear froglets, not only the hatching, but all the most conspicuous metamorphosis, being completed inside the body of the mother before birth. Among insects that depend on opportunistic exploitation of transient food sources, such as many Sarcophagidae and other carrion flies, and species such as many Calliphoridae, that rely on fresh dung, and parasitoids such as tachinid flies that depend on entering the host as soon as possible, the embryos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Galeorhinus Galeus
The school shark (''Galeorhinus galeus'') is a houndshark of the family Triakidae, and the only living member of the genus '' Galeorhinus''. Common names also include tope, tope shark, snapper shark, and soupfin shark. It is found worldwide in temperate seas at depths down to about . It can grow to nearly long. It feeds both in midwater and near the seabed, and its reproduction is ovoviviparous. This shark is caught in fisheries for its flesh, its fins, and its liver, which has a very high vitamin A content. The IUCN has classified this species as critically endangered in its Red List of Threatened Species. Taxonomy The school shark is the only extant member of '' Galeorhinus'', an ancient genus that dates to at least the Early Eocene, when the very similar species '' G. cuvieri'' is known, and likely as far back as the mid-Cretaceous. Fossil teeth of the modern school shark date as far back as the mid-late Eocene, where they are known from the Castle Hayne Formation of N ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fin Needles
A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foils that produce lift or thrust, or provide the ability to steer or stabilize motion while traveling in water, air, or other fluids. Fins are also used to increase surface areas for heat transfer purposes, or simply as ornamentation. Fins first evolved on fish as a means of locomotion. Fish fins are used to generate thrust and control the subsequent motion. Fish and other aquatic animals, such as cetaceans, actively propel and steer themselves with pectoral and tail fins. As they swim, they use other fins, such as dorsal and anal fins, to achieve stability and refine their maneuvering.Helfman G, Collette BB, Facey DE and Bowen BW (2009"Functional morphology of locomotion and feeding" Chapter 8, pp. 101–116. In:''The Diversity of Fishes: Biology'', John Wiley & Sons. . The fins on the tails of cetaceans, ichthyosaurs, metriorhynchids, mosasaurs and plesiosaurs are c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Houndshark
The Triakidae or houndsharks are a family of ground sharks, consisting of about 40 species in nine genera. In some classifications, the family is split into two subfamilies, with the genera ''Mustelus'', '' Scylliogaleus'' and '' Triakis'' in the subfamily Triakinae, and the remainders in the subfamily Galeorhininae. Houndsharks are distinguished by possessing two large, spineless dorsal fins, an anal fin and oval eyes with nictitating eyelids. They are small to medium in size, ranging from in adult length. They are found throughout the world in warm and temperate waters, where they feed on small fish and invertebrates on the seabed and in midwater. Fossil records of this group date back to the Cenomanian. Genera Houndsharks are classified into subfamilies and genera as follows: * Galeorhininae Gill, 1862 ** '' Furgaleus'' Whitley, 1951 (whiskery shark) ** '' Galeorhinus'' Blainville, 1816 (school shark) ** '' Gogolia'' Compagno, 1973 (sailback houndshark) ** ''Hemitriak ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Braised Dogfish
Braising (from the French word ''braiser'') is a combination-cooking method that uses both wet and dry heats: typically, the food is first browned at a high temperature, then simmered in a covered pot in cooking liquid (such as wine, broth, coconut milk or beer). It is similar to stewing, but braising is done with less liquid and usually used for larger cuts of meat. Braising of meat is often referred to as pot roasting, though some authors make a distinction between the two methods, based on whether additional liquid is added. Osso buco and coq au vin are well known braised meat dishes, and the technique can also be used to prepare fish, tempeh, tofu, or fruits and vegetables. Techniques Most braises follow the same basic steps. The food to be braised (meats, vegetables, mushrooms, etc.) is first pan-seared to brown its surface and enhance its flavor (through the Maillard reaction). If the food will not produce enough liquid of its own, a certain amount of cooking liquid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vertebra
Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal segment and the particular species. The basic configuration of a vertebra varies; the vertebral body (also ''centrum'') is of bone and bears the load of the vertebral column. The upper and lower surfaces of the vertebra body give attachment to the intervertebral discs. The posterior part of a vertebra forms a vertebral arch, in eleven parts, consisting of two pedicles (pedicle of vertebral arch), two laminae, and seven processes. The laminae give attachment to the ligamenta flava (ligaments of the spine). There are vertebral notches formed from the shape of the pedicles, which form the intervertebral foramina when the vertebrae articulate. These foramina are the entry and exit conduits for the spinal nerves. The body of the vertebr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pelvic Fin
Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hindlimbs of tetrapods, which evolved from lobe-finned fish during the Middle Devonian. Structure and function Structure In actinopterygians, the pelvic fin consists of two endochondrally-derived bony girdles attached to bony radials. Dermal fin rays ( lepidotrichia) are positioned distally from the radials. There are three pairs of muscles each on the dorsal and ventral side of the pelvic fin girdle that abduct and adduct the fin from the body. Pelvic fin structures can be extremely specialized in actinopterygians. Gobiids and lumpsuckers modify their pelvic fins into a sucker disk that allow them to adhere to the substrate or climb structures, such as waterfalls. In priapiumfish, males have modified their pelvic structures into ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neoteny
Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the Physiology, physiological, or Somatic (biology), somatic, development of an organism, typically an animal. Neoteny in humans, Neoteny in modern humans is more significant than in other primates. In progenesis or paedogenesis, sexual development is accelerated. Both neoteny and progenesis result in paedomorphism (as having the form typical of children) or paedomorphosis (changing towards forms typical of children), a type of heterochrony. It is the retention in adults of traits previously seen only in the young. Such retention is important in evolutionary biology, domestication, and evolutionary developmental biology. Some authors define paedomorphism as the retention of larval traits, as seen in salamanders.Schell, S. C. ''Handbook of Trematodes of North America North of Mexico'', 1985, pg. 22 History and etymology Julius Kollmann created the term ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cloaca
A cloaca ( ), : cloacae ( or ), or vent, is the rear orifice that serves as the only opening for the digestive (rectum), reproductive, and urinary tracts (if present) of many vertebrate animals. All amphibians, reptiles, birds, cartilaginous fish and a few mammals ( monotremes, afrosoricids, and marsupial moles, etc.) have this orifice, from which they excrete both urine and feces; this is in contrast to most placental mammals, which have separate orifices for evacuation and reproduction. Excretory openings with analogous purpose in some invertebrates are also sometimes called cloacae. Mating through the cloaca is called cloacal copulation and cloacal kissing. The cloacal region is also often associated with a secretory organ, the cloacal gland, which has been implicated in the scent-marking behavior of some reptiles, marsupials, amphibians, and monotremes. Etymology The word is from the Latin verb ''cluo'', "(I) cleanse", thus the noun ''cloaca'', " sewer, drain" ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clasper
In biology, a clasper is a male anatomical structure found in some groups of animals, used in mating. Male cartilaginous fish have claspers formed from the posterior portion of their pelvic fin which serve to channel semen into the female's cloaca during mating. The act of mating in some fish including sharks usually includes one of the claspers raised to allow water into the siphon through a specific orifice. The clasper is then inserted into the cloaca, where it opens like an umbrella to anchor its position. The siphon then begins to contract, expelling water and sperm. The claspers of many shark species have spines or hooks, which may hold them in place during copulation. Many male holocephalans, including living chimaeras, have cephalic claspers (tenacula) on their heads, which are thought to aid in holding the female during mating. In entomology Entomology (from Ancient Greek ἔντομον (''éntomon''), meaning "insect", and -logy from λόγος (''lógos'') ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Countershading
Countershading, or Thayer's law, is a method of camouflage in which animal coloration, an animal's coloration is darker on the top or upper side and lighter on the underside of the body. This pattern is found in many species of mammals, reptiles, birds, fish, and insects, both in predators and in prey. When light falls from above on a uniformly coloured three-dimensional object such as a sphere, it makes the upper side appear lighter and the underside darker, grading from one to the other. This pattern of light and shade makes the object appear solid, and therefore easier to detect. The classical form of countershading, discovered in 1909 by the artist Abbott Handerson Thayer, works by counterbalancing the effects of self-shadowing, again typically with grading from dark to light. In theory this could be useful for military camouflage, but in practice it has rarely been applied, despite the best efforts of Thayer and, later, in the Second World War, of the zoologist Hugh Cott. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
