Gastrula

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gastrula

[′ga·strə·lə]
(embryology)
The stage of development in animals in which the endoderm is formed and invagination of the blastula has occurred.

Gastrula

 

one of the stages of embryonic development in multicellular animals. In the gastrula stage the embryo has a two-layer wall and cavity (gastrocoel) that communicates with the surrounding environment by means of an opening, the blastopore. The outer wall is called the ectoderm; the inner wall, the endoderm. They are the primordial embryonic layers. In the beginning the endoderm, and less frequently the ectoderm, also contains the material for a middle layer of tissue—the mesoderm. At the end of gastrulation, the mesoderm separates and becomes independent, and the embryo is transformed from a two-layer to a three-layer organization.

The transformation from the blastula to the gastrula takes place differently in different animals. Already at the gastrula stage, certain differences in the properties of the embryonic layers that are precursors of their morphological differentiation can be observed. The differences in structure of the embryos of different animals at this stage of development are determined both by the structure of the eggs and by the different modes of existence of the embryos. In most animals the embryo spends the gastrula stage in the egg envelope or in the mother’s body; in some hydrozoans the gastrula is a free-living larva. Sometimes the differences pertain to the most general features; for example, in the embryos of bony fish the gastrocoel is lacking, and in certain coelenterate gastrulae the blastopore is lacking. The presence of the gastrula stage (with its characteristic separation into embryonic tissues) in the development of all multicellular organisms was demonstrated by A. O. Kovalevskii and E. Metchnikoff and provided proof of the common origin of animals.

T. A. DETLAF

References in periodicals archive ?
After the incubation, gastrulae were liberated from the jelly coat and egg capsules by finely mincing the egg strands with a razor blade.
californica gastrulae per slide were needed to obtain at least 10 single nuclei not associated with any cellular debris or at least 10 well-spaced metaphase chromosome spreads.
cidaris), pits on the ectoderm of gastrulae, a mouth that opens late in the two-arm pluteus stage, and juvenile spine morphology.
Usherin is expressed in gastrulae, planulae, and polyps
Using methods identical to those employed to collect the data illustrated in Figure 4, additional experiments (total n = 7) were conducted on different batches (gametes from different parents) of blastulae, gastrulae, and larvae of S.
Gastrulae and early planulae stages were also observed sooner at 30 and 31.5 [degrees]C than at 28 [degrees]C, but statistical analyses could not be run due to small sample sizes.
The gastrulae developed into bipinnaria-like larvae 36 h after insemination.
This rate increased at gastrulation and ranged (n = 2) from 7.0% to 7.2% embry[o.sup.-1] [h.sup.-1] in 10-day-old gastrulae. In later larval stages that were unfed for 43 days, fractional rates of synthesis decreased and ranged (n = 2) from 0.4% to 0.5% larv[a.sup.-1] [h.sup.-1].
Of ciliary swimmers, some asteroids first swim as bla stulae, others as gastrulae; spiralians swim before or after gastrulation, or even as veliger larvae.