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The center of Hensen's node contains a funnel-shaped depression, the primitive pit, where the cells of the epiblast (the upper layer of embryonic cells) initially begin to invaginate. This invagination expands posteriorly into the primitive groove as the cell layers continue to move into the space between the embryonic cells and the yolk.
The result is cell movement through the fluid medium. Furthermore, the direction of movement is determined by chemotaxis. When chemoattraction occurs in a particular area of the cell membrane, actin polymerization can begin and move the cell in that direction. [9] An excellent example of an organism that utilizes pseudopods is Naegleria fowleri ...
The three modern orders are Anura (the frogs), Caudata (or Urodela, the salamanders), and Gymnophiona (or Apoda, the caecilians). [15] It has been suggested that salamanders arose separately from a temnospondyl-like ancestor, and even that caecilians are the sister group of the advanced reptiliomorph amphibians, and thus of amniotes. [16]
Anura is an order of animals in the class Amphibia that includes frogs and toads. More than 5,000 species are described in the order. The living anurans are typically divided into three suborders: Archaeobatrachia, Mesobatrachia, and Neobatrachia. This classification is based on such morphological features as the number of vertebrae, the ...
Cells communicate, which means that the type of environment of specific cells implies their future roles in the development of the embryo. Cell movements during amphibian gastrulation In frog embryos, gastrulation initiates at the site identified as the gray crescent, located on the future dorsal side of the embryo, slightly below the ...
[3] Other terms sometimes used to refer to the water vascular system are "ambulacral system" [4] [5] [6] and "aquiferous system". In the past, "aquiferous system" was also used to refer to many unrelated invertebrate structures, [7] [8] but today, it is restricted to water channels in sponges [9] and the hydrostatic skeleton of some mollusks ...
The Lissamphibia (from Greek λισσός (lissós, "smooth") + ἀμφίβια (amphíbia), meaning "smooth amphibians") is a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: the Salientia (frogs and their extinct relatives), the Caudata (salamanders and their extinct relatives), and the ...
Temnospondyli (from Greek τέμνειν, temnein 'to cut' and σπόνδυλος, spondylos 'vertebra') or temnospondyls is a diverse ancient order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carboniferous, Permian and Triassic periods, with fossils being found on every continent.