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Related to ectoderm: mesoderm


layer of cells that covers the surface of an animal embryo after the process of gastrulation has occurred. This outer layer, together with the endodermendoderm
, in biology, inner layer of tissue formed in the gastrula stage of the developing embryo. At the end of the blastula stage, cells of the embryo are arranged in the form of a hollow ball.
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, or inner layer, is present in all early embryos. In the development of animals of the phyla PoriferaPorifera
[Lat.,=pore bearer], animal phylum consisting of the organisms commonly called sponges. It is the only phylum of the animal subkingdom Parazoa and represents the least evolutionarily advanced group of the animal kingdom.
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, CtenophoraCtenophora
, a small phylum of exclusively marine, invertebrate animals, commonly known as comb jellies. Because they are so delicate that specimens are difficult to collect, little was known about them until the advent of blue-water scuba and submersible collecting.
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, and CnidariaCnidaria
or Coelenterata
, phylum of invertebrate animals comprising the sea anemones, corals, jellyfish, and hydroids. Cnidarians are radially symmetrical (see symmetry, biological).
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, these two primary layers give rise to all the tissues and organs of the animals, a process known as diploblastic development. In higher animals, such as those of the phyla EchinodermataEchinodermata
[Gr.,=spiny skin], phylum of exclusively marine bottom-dwelling invertebrates having external skeletons of calcareous plates just beneath the skin. The plates may be solidly fused together, as in sea urchins, loosely articulated to facilitate movement, as in sea
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 and ChordataChordata
, phylum of animals having a notochord, or dorsal stiffening rod, as the chief internal skeletal support at some stage of their development. Most chordates are vertebrates (animals with backbones), but the phylum also includes some small marine invertebrate animals.
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, a third, middle layer, the mesodermmesoderm,
in biology, middle layer of tissue formed in the gastrula stage of the developing embryo. At the end of the blastula stage, cells of the embryo are arranged in the form of a hollow ball.
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, is formed between the ectoderm and endoderm during gastrulation, and the process is termed triploblastic development. In most embryos, differentiation of ectodermal tissue gives rise to epidermis and its specialized structures (scales, feathers, nails, and hair); some exocrine glands (sweat and sebaceous glands); some endocrine glands (the pineal body and the pituitary gland); the nervous system; and the organs of special sense (ear and eye). In animals of some phyla, such as the MolluscaMollusca
, taxonomic name for the one of the largest phyla of invertebrate animals (Arthropoda is the largest) comprising more than 50,000 living mollusk species and about 35,000 fossil species dating back to the Cambrian period.
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 and AnnelidaAnnelida
[Lat., anellus=a ring], phylum of soft-bodied, bilaterally symmetrical (see symmetry, biological), segmented animals, known as the segmented, or annelid, worms.
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, the fate of particular cells of the embryo is determined in the earliest stages of the fertilized egg and may even be fixed at or before fertilization.



(1) The outermost germ layer; the external layer of the embryo of multicellular animals in the gastrular stage. From the ectoderm are formed the integuments, nervous system, sensory organs, anterior and posterior sections of the digestive tract, external gills, and ectomesenchyme. In the Deuterostomia, all the elements derived from the ectoderm are formed as a result of the action upon it of the chordomesoderm, the entoderm, and their derivatives.

(2) The external wall of the body of coelenterates. The ectoderm consists of a single layer of cells—epithelial, epithelio-muscular, interstitial, and sensory cells, as well as stinging capsules.


The outer germ layer of an animal embryo. Also known as epiblast.
(invertebrate zoology)
The outer layer of a diploblastic animal.
References in periodicals archive ?
The ectoderm first differentiates the brain and nervous system tissue, then forms the endoderm, which produces the internal mucous membranes and a number of endocrine glands (such as the thyroid and the thymus) and exocrine glands (such as the pancreas).
Dynamic expression of chicken Sox2 and Sox3 genes in ectoderm induced to form neural tissue.
Histological analysis of this region indicated that spine formation began with the formation of a central, longitudinal depression in the ectoderm (Fig.
To say that derivatives of the embryonic ectoderm are involved means that the hair, nails, teeth, sweat glands, and other such structures are abnormally formed.
ESCs can also be derived from a type of human tumor called a teratoma A teratoma is a germ cell tumor comprised of elements of different types of tissue from one or more of the three germ cell layers, which include the endoderm, mesoderm and ectoderm.
One condition that exhibits missing teeth is hereditary hypohidrotic ectodermal dysplasia, the best known of a group of genetic conditions in which at least two derivatives of the ectoderm (teeth, hair, nails, glands) are deficient in function or absent altogether.
The ectoderm, which produces the skin and nervous system
11] Neurulation occurs as the ectoderm folds to form the neural tube.
These results indicate that cells derived from both the mesoderm and ectoderm are required for establishing the normal distribution of axonal process, and that a subset of neuroectodermal cells that express the leech engrailed-class gene are required for forming the posterior segmental nerve
Other cellular action during and after migration through the primitive streak is controlled by various compounds produced by the ectoderm (Developmental Biology 234-41).
It is the first step toward gastrulation, in which an outer layer of cells dimples inward at what will be either the mouth or anus to form the three distinct precursor cell types shared by most animals: the ectoderm, or outer layer, which forms neurons, skin cells and pigment; the endoderm, or inner layer, which forms many of the organs; and mesoderm, or middle layer, which forms muscle and red blood cells.
We investigated EB formation and differentiation capacity into the three germ layers, such as endoderm, mesoderm, and ectoderm.