Eckelbarger Kevin J, Grassle Judith P
Biol Bull. 1983 Oct;165(2):379-393. doi: 10.2307/1541203.
Ultrastructural studies of ovarian follicle cells and mature eggs in four sibling species in the polychaete genus Capitella have revealed distinct and consistent morphological differences that parallel in some respects the differences between the species in egg size, and embryonic and larval development. Capitella spp. I and II are extremely similar in all respects: the follicle cells lack lipid and contain a modest amount of glycogen; the mature eggs are rich in lipid and glycogen and contain very similar proteid yolk granules. In both species mature eggs have a characteristic electron-dense band and a zone of mitochondria in the cortical ooplasm. These sympatric species have eggs that are similar in size and lecithotrophic larvae that are planktonic for only a short time. Capitella sp. III (Capitella jonesi) has ovarian follicle cells containing a small amount of lipid and no glycogen, while the mature eggs have a small amount of lipid, abundant glycogen, and large proteid yolk granules. These small eggs show no evidence of an electron-dense band or any concentration of mitochondria in the cortical ooplasm. This species has planktotrophic larvae that remain in the plankton for many weeks. Capitella sp. IIIa has ovarian follicle cells rich in both lipid and glycogen. The large mature eggs are rich in lipid, have relatively little glycogen, and have abundant proteid yolk granules. The cortical ooplasm contains electron-dense material similar to that observed in the eggs of species I and II but it is distributed in a discontinuous band. This species has direct development, and juvenile worms emerge from the parental brood tube after metamorphosis. The egg envelopes and microvilli of the eggs of all four sibling species undergo substantial morphological changes following release from the ovary into the coelom. The significance of these morphological and biochemical differences between the species is not known, but the lack of intraspecific variation in these characters suggests that their presence or absence reflects specific differences in the processes of yolk formation and utilization.
对多毛纲小头虫属四个姊妹种的卵泡细胞和成熟卵的超微结构研究表明，存在明显且一致的形态学差异，这些差异在某些方面与物种间卵大小、胚胎及幼虫发育的差异相似。小头虫属I和II在各方面都极为相似：卵泡细胞不含脂质，含有适量糖原；成熟卵富含脂质和糖原，含有非常相似的蛋白质卵黄颗粒。在这两个物种中，成熟卵在皮质卵质中都有一条特征性的电子致密带和一个线粒体区域。这些同域分布的物种卵大小相似，其卵黄营养型幼虫仅在浮游阶段停留很短时间。小头虫属III（琼斯小头虫）的卵泡细胞含有少量脂质且无糖原，而成熟卵含有少量脂质、丰富的糖原和大的蛋白质卵黄颗粒。这些小卵没有电子致密带的迹象，也没有线粒体在皮质卵质中的任何聚集。该物种有浮游营养型幼虫，在浮游阶段停留数周。小头虫属IIIa的卵泡细胞富含脂质和糖原。大的成熟卵富含脂质，糖原相对较少，有丰富的蛋白质卵黄颗粒。皮质卵质含有与I和II物种卵中观察到的类似的电子致密物质，但呈不连续带分布。该物种直接发育，幼体在变态后从亲体的育儿管中孵出。所有四个姊妹种的卵从卵巢释放到体腔后，其卵膜和微绒毛都会发生显著的形态变化。这些物种间形态和生化差异的意义尚不清楚，但这些特征缺乏种内变异表明它们的存在或缺失反映了卵黄形成和利用过程中的特定差异。
