. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 1. Fertilisation and cleavage of Op/iioiiereis schaveri. (a) Fertilized eggs have a raised fertilization membrane (FM) and large perivitelline space (arrow), (b) Fertilized eggs and four-cell embryos. Scale bars = 100 tun. and embedded in Spurr's resin at 80°C for 20 h. Larvae were serial sectioned at /im and stained with 1% tolu- idine blue in ethanolamine. Results Early development Fertilized eggs had a 50-jum-wide perivitelline space between the oolemma and the fertilization envelope (Fig. la, b). Althou
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Figure 1. Fertilisation and cleavage of Op/iioiiereis schaveri. (a) Fertilized eggs have a raised fertilization membrane (FM) and large perivitelline space (arrow), (b) Fertilized eggs and four-cell embryos. Scale bars = 100 tun. and embedded in Spurr's resin at 80°C for 20 h. Larvae were serial sectioned at /im and stained with 1% tolu- idine blue in ethanolamine. Results Early development Fertilized eggs had a 50-jum-wide perivitelline space between the oolemma and the fertilization envelope (Fig. la, b). Although looked for, polar bodies were never ob- served, indicating that meiosis is completed during ovula- tion and spawning. Cleavage was initially equal and radial (Fig. 2a). After second cleavage, however, the division planes became offset, resulting in an irregular arrangement of the blastomeres (Fig. 2b). Beyond third cleavage, cell division became asynchronous, with some cells cleaving before others (Fig. 2b). The irregular arrangement of blas- tomeres remained evident to the blastula stage. About 12 h after fertilization, the embryos took on a slightly contorted shape as they developed into wrinkled blastulae. The wrin- kles were shallow, forming slight indentations in the epi- thelium (Fig. 2c). The blastulae subsequently smoothed (Fig. 2d), the epithelium became uniformly ciliated, and the embryos started to rotate within the fertilization envelope. The blastulae hatched about 16 h after fertilization and swam with their anterior pole forward, in no particular direction or orientation. Gastrulation occurred about 21 h after fertilization by invagination of the vegetal plate (Fig. 2e). During gastrulation, the epithelial cells changed shape from cuboidal (Fig. 2d) to columnar (Fig. 2f). Round cells in the epithelium, which were situated towards the apical surface, may be recently divided cells (Fig. 2f). Lipid drop- lets in the eggs of O. scluiveri were about 3 in diam
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
