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Acanthodii

Acanthodii  

Class of primitive, fossil fish that had a true bony skeleton, a heterocercal tail fin, a persistent notochord, ganoid scales, and stout spines in front of the fins. The acanthodians lived from the ...
Actinopterygii

Actinopterygii  

; class Osteichthyes)A subclass of ray-finned fish, that includes the majority of living bony fish of sea and fresh water. The fins are composed of a membranous web of skin supported by a varying ...
Andreas Vesalius

Andreas Vesalius  

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(1514–64)Belgian physician and anatomist, who was a professor at Padua for six years before becoming a physician to the Habsburg court. He is remembered for producing in 1538–43 definitive text and ...
cartilage bone

cartilage bone  

Bone that is formed by replacing the cartilage of an embryo skeleton. The process, called endochondral ossification, is brought about by the cells (osteoblasts) that secrete bone. Compare membrane ...
cartilaginous fish

cartilaginous fish  

Fish in which the skeleton, including the skull and jaws, consists entirely of cartilage and never, even in the adult stage, comprises bony tissue. Sharks and rays (Chondrichthyes) have a ...
Craniata

Craniata  

(kingdom Metazoa, phylum Chordata)The subphylum that comprises animals that have a bony or cartilaginous skull and a dorsal vertebral column. See also Vertebrata.http://www.tolweb.org/Craniata ...
fin ray

fin ray  

A rod-like support of the fin membrane, composed of cartilage in lampreys, horny fibres in sharks, and bone in bony fish.
Heterostraci

Heterostraci  

(superclass Agnatha)Oldest known vertebrate order of jawless, heavily armoured fish-like forms, ranging from the Upper Cambrian to the Devonian. The dermal plates of the body lacked true bone cells ...
membrane bone

membrane bone  

A bone that develops in connective tissue by direct ossification, without cartilage being formed first. The bones of the face and skull are membrane bones.
osteoid

osteoid  

A soft material, consisting mainly of collagen, that is secreted by osteoblasts and constitutes the uncalcified matrix of bone. Osteoid is converted into hard bone matrix when it combines with ...
phosphorite

phosphorite  

A sedimentary rock rich in phosphate, usually in the form of carbonate hydroxyl fluorapatite (Ca10(PO4CO3)6F2–3). Phosphorites occur as nodules and crusts formed in oceanic areas where sedimentation ...
phosphorus

phosphorus  

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n. a nonmetallic element. Phosphorus compounds are major constituents in the tissues of both plants and animals. In humans, phosphorus is mostly concentrated in bone. However, certain ...
Pteraspidomorphi

Pteraspidomorphi  

(superclass Agnatha)A class of jawless vertebrates that have an eel-like body, lack paired fins, have two semicircular canals, and a skeleton not consisting of true bone. The class includes the ...
sensory receptors

sensory receptors  

An anatomical structure composed of sensory nerve endings adapted to respond to specific stimuli (1) and to convert them into nerve impulses that are transmitted to other parts of the nervous system, ...
skeletal material

skeletal material  

In most vertebrates the skeleton is made from bone (calcium phosphate); among invertebrates it is more varied. Calcite or aragonite in various forms is common in such groups as the brachiopods ...
sun

sun  

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The central star (G spectral type) in the solar system, 696 000 km in radius, 333 000 × Earth mass, 1 300 000 × Earth volume, and with a mean density of 1410 kg/m3. The equator is inclined at 7.25° ...
Teleostei

Teleostei  

The major superorder of the Osteichthyes (bony fish), containing about 20 000 species. Teleosts have colonized an extensive variety of habitats and show great diversity of form. The group includes ...

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