Development of <i>Oulastrea crispata</i>.

<p>(A) Spawned egg. (B) 2-cell stage. (C) At the 4-cell stage the blastomeres are offset. (D) 8-cell stage. (E) 16-cell stage. (F) Another embryo at the 16 cell stage. (G) This embryo has started to flatten. The blastocoel is apparent by the lightening at the center of the embryo. (H) By this stage the ectodermal cells are becoming columnar rather than circular in outline. The central blastocoel is apparent. (I-L) As cell division continues the flattened spheroid gradually resumes a spherical shape. (M) Pear-shaped planula. (N) Invagination (inv) has started at the oral end of the planula. (O) There is a ledge-like constriction at the oral end of the planula and the aboral end has thickened in preparation for settlement. (P) The constriction at the oral end of the planula is now less sharp and has moved aborally, the aboral end has become more rounded and the oral pore is now clearly apparent. In M-P the blastopore/oral pore is marked with an asterisk.