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Notocord
The notochord is an elastic, rod-like structure found in chordates. In vertebrates the notochord is an embryonic structure that disintegrates, as the vertebrae develop, to become the nucleus pulposus in the intervertebral discs of the vertebral column. In non-vertebrate chordates a notochord persists. The notochord is derived from the embryonic mesoderm and consists of an inner core of vacuolated cells filled with glycoproteins, covered by two helical collagen-elastin sheaths. It lies longitudinally along the rostral-caudal (head to tail) axis of the body, dorsal to the gut tube, and ventral to the dorsal nerve cord. Some chordate invertebrates, such as tunicates, develop a notochord during the larval stage but lose it through subsequent stages into adulthood. The notochord is important for signaling the dorso-ventral patterning of cells coming from the mesodermal progenitors. This helps form the precursors needed for certain organs and the embryo to develop. In summary ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Axial Mesoderm
Axial mesoderm, or chordamesoderm, is the mesoderm in the embryo that lies along the central axis under the neural tube. * will give rise to notochord * starts as the notochordal process, whose formation finishes at day 20 in humans. * important not only in forming the notochord itself but also in inducing development of the overlying ectoderm into the neural tube * will eventually induce the formation of vertebral bodies. * ventral floor of the notochordal process fuses with endoderm. * The notochord will form the nucleus pulposus of intervertebral discs. There is some discussion as to whether these cells contributed from the notochord are replaced by others from the adjacent mesoderm. It gives rise to the notochordal process, which later becomes the notochord The notochord is an elastic, rod-like structure found in chordates. In vertebrates the notochord is an embryonic structure that disintegrates, as the vertebrae develop, to become the nucleus pulposus in the inter ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dorsal (anatomy)
Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. This position provides a definition of what is at the front ("anterior"), behind ("posterior") and so on. As part of defining and describing terms, the body is described through the use of anatomical planes and anatomical axes, axes. The meaning of terms that are used can change depending on whether a vertebrate is a biped or a quadruped, due to the difference in the neuraxis, or if an invertebrate is a non-bilaterian. A non-bilaterian has no anterior or posterior surface for example but can still have a descriptor used such as proximal or distal in relation to a body part that is nearest to, or furthest from its middle. International organisations have determined vocabularies that are often used as standards for subdisciplines of anatomy. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Vertebral Column
The spinal column, also known as the vertebral column, spine or backbone, is the core part of the axial skeleton in vertebrates. The vertebral column is the defining and eponymous characteristic of the vertebrate. The spinal column is a segmented column of vertebrae that surrounds and protects the spinal cord. The vertebrae are separated by intervertebral discs in a series of cartilaginous joints. The dorsal portion of the spinal column houses the spinal canal, an elongated body cavity, cavity formed by the alignment of the vertebral neural arches that encloses and protects the spinal cord, with spinal nerves exiting via the intervertebral foramina to innervate each body segment. There are around 50,000 species of animals that have a vertebral column. The human spine is one of the most-studied examples, as the general structure of human vertebrae is fairly homology (biology), typical of that found in other mammals, reptiles, and birds. The shape of the vertebral body does, howev ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cartilaginous
Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck and the bronchial tubes, and the intervertebral discs. In other taxa, such as chondrichthyans and cyclostomes, it constitutes a much greater proportion of the skeleton. It is not as hard and rigid as bone, but it is much stiffer and much less flexible than muscle. The matrix of cartilage is made up of glycosaminoglycans, proteoglycans, collagen fibers and, sometimes, elastin. It usually grows quicker than bone. Because of its rigidity, cartilage often serves the purpose of holding tubes open in the body. Examples include the rings of the trachea, such as the cricoid cartilage and carina. Cartilage is composed of specialized cell ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bone
A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and enable mobility. Bones come in a variety of shapes and sizes and have complex internal and external structures. They are lightweight yet strong and hard and serve multiple functions. Bone tissue (osseous tissue), which is also called bone in the uncountable sense of that word, is hard tissue, a type of specialised connective tissue. It has a honeycomb-like matrix internally, which helps to give the bone rigidity. Bone tissue is made up of different types of bone cells. Osteoblasts and osteocytes are involved in the formation and mineralisation of bone; osteoclasts are involved in the resorption of bone tissue. Modified (flattened) osteoblasts become the lining cells that form a protective layer on the bone surface. The mine ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hagfish
Hagfish, of the Class (biology), class Myxini (also known as Hyperotreti) and Order (biology), order Myxiniformes , are eel-shaped Agnatha, jawless fish (occasionally called slime eels). Hagfish are the only known living Animal, animals that have a skull but no vertebral column, although they do have rudimentary vertebrae. Hagfish are marine animal, marine predators and scavengers that can defend themselves against other larger predators by releasing copious amounts of slime coat, slime from mucous glands in their skin. Although their exact relationship to the only other extant taxon, living group of Agnatha, jawless fish, the lampreys, was long the subject of controversy, genetic evidence suggests that hagfish and lampreys are more closely related to each other than to jawed vertebrates, thus forming the superclass Cyclostomi. The oldest-known stem group hagfish are known from the Pennsylvanian (geology), Late Carboniferous, around Moscovian (Carboniferous), 310 million years ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lancelet
The lancelets ( ), also known as amphioxi (: amphioxus ), consist of 32 described species of somewhat fish-like benthic filter feeding chordates in the subphylum Cephalochordata, class Leptocardii, and family Branchiostomatidae. Lancelets diverged from other chordates during or prior to the Cambrian period. A number of fossil chordates have been suggested to be closely related to lancelets, including ''Pikaia'' and ''Cathaymyrus'' from the Cambrian and ''Palaeobranchiostoma'' from the Permian, but their close relationship to lancelets has been doubted by other authors. Molecular clock analysis suggests that modern lancelets probably diversified much more recently, during the Cretaceous or Cenozoic. They are of interest to List of authors of names published under the ICZN, Zoologists as lancelets contain many organs and organ systems that are Homology (biology), homologous to those of modern fish. Therefore, they provide a number of examples of possible evolutionary exaptation. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cephalochordate
The lancelets ( ), also known as amphioxi (: amphioxus ), consist of 32 described species of somewhat fish-like benthic filter feeding chordates in the subphylum Cephalochordata, class Leptocardii, and family Branchiostomatidae. Lancelets diverged from other chordates during or prior to the Cambrian period. A number of fossil chordates have been suggested to be closely related to lancelets, including '' Pikaia'' and '' Cathaymyrus'' from the Cambrian and '' Palaeobranchiostoma'' from the Permian, but their close relationship to lancelets has been doubted by other authors. Molecular clock analysis suggests that modern lancelets probably diversified much more recently, during the Cretaceous or Cenozoic. They are of interest to Zoologists as lancelets contain many organs and organ systems that are homologous to those of modern fish. Therefore, they provide a number of examples of possible evolutionary exaptation. For example, the gill-slits of lancelets are used for feeding only ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Endoskeleton
An endoskeleton (From Ancient Greek ἔνδον, éndon = "within", "inner" + σκελετός, skeletos = "skeleton") is a structural frame (skeleton) — usually composed of mineralized tissue — on the inside of an animal, overlaid by soft tissues. Endoskeletons serve as structural support against gravity and mechanical loads, and provide anchoring attachment sites for skeletal muscles to transmit force and allow movements and locomotion. Vertebrates and the closely related cephalochordates are the predominant animal clade with endoskeletons (made of mostly bone and sometimes cartilage, as well as notochordal glycoprotein and collagen fibers), although invertebrates such as sponges also have evolved a form of "rebar" endoskeletons made of diffuse meshworks of calcite/silica structural elements called spicules, and echinoderms have a dermal calcite endoskeleton known as ossicles. Some coleoid cephalopods (squids and cuttlefish) have an internalized vestigial aragon ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Embryonic Development
In developmental biology, animal embryonic development, also known as animal embryogenesis, is the developmental stage of an animal embryo. Embryonic development starts with the fertilization of an egg cell (ovum) by a sperm, sperm cell (spermatozoon). Once fertilized, the ovum becomes a single diploid cell known as a zygote. The zygote undergoes mitosis, mitotic cell division, divisions with no significant growth (a process known as cleavage (embryo), cleavage) and cellular differentiation, leading to development of a multicellular embryo after passing through an organizational checkpoint during mid-embryogenesis. In mammals, the term refers chiefly to the early stages of prenatal development, whereas the terms fetus and fetal development describe later stages. The main stages of animal embryonic development are as follows: * The zygote undergoes a series of cell divisions (called cleavage) to form a structure called a morula. * The morula develops into a structure called a bla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Larva
A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase of their life cycle. A larva's appearance is generally very different from the adult form (''e.g.'' caterpillars and butterflies) including different unique structures and organs that do not occur in the adult form. Their diet may also be considerably different. In the case of smaller primitive arachnids, the larval stage differs by having three instead of four pairs of legs. Larvae are frequently adapted to different environments than adults. For example, some larvae such as tadpoles live almost exclusively in aquatic environments but can live outside water as adult frogs. By living in a distinct environment, larvae may be given shelter from predators and reduce competition for resources with the adult population. Animals in the lar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tunicate
Tunicates are marine invertebrates belonging to the subphylum Tunicata ( ). This grouping is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time called Urochordata, and the term urochordates is still sometimes used for these animals. Despite their simple appearance and very different adult form, their close relationship to the vertebrates is certain. Both groups are chordates, as evidenced by the fact that during their mobile larval stage, tunicates possess a notochord, a hollow dorsal nerve cord, pharyngeal slits, post-anal tail, and an endostyle. They resemble a tadpole. Tunicates are the only chordates that have lost their Myomere, myomeric segmentation, with the possible exception of the seriation of the gill slits. However, Doliolida, doliolids still display segmentation of the muscle bands. Some tunicates live as solitary individuals, but others replicate by budding and be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
