The two modes of development in sea urchins are direct development, in which the adult develops directly from the gastrula to the adult and does not feed, and indirect development, in which the adult develops indirectly through a feeding larva. In this account of the indirect, feeding larva of Heliocidaris tuberculata, the question raised is whether an evolutionary difference of unequal cell divisions contributes to the development of feeding structures in the indirect larva. In indirect development, the cell divisions at the fourth and fifth cell cycles of the zygote are unequal, with four small micromeres formed at the vegetal pole at the fifth cell division. In direct development, these cell divisions are not unequal. From their position at the head of the archenteron, the small micromeres are strategically located to contribute to the feeding tissues of the larva and the adult of H. tuberculata.

中文翻译：

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海胆Heliocidaris tuberculata的摄食幼虫的早期发育：小型微生物的作用。

海胆的两种发育方式是直接发育和间接发育，其中成年后从腹足直接发育到成年后不进食，间接发育中成年后通过喂食幼虫间接发育。由于这种原因，Heliocidaris tuberculata的间接摄食幼虫，提出的问题是，不等细胞分裂的进化差异是否有助于间接幼虫的进食结构的发育。在间接发育中，合子在第四和第五个细胞周期的细胞分裂是不相等的，在第五个细胞分裂的植物极处形成了四个小的微粒。在直接开发中，这些细胞分裂并非不平等。从它们在弓形虫头部的位置出发，这些微小的小动物在策略上处于有利位置，可以为幼虫和结核杆菌的成虫提供食物。