Phreodrilidae is a small family uniting about 50 species of minute freshwater clitellate annelids inhabiting mainly the Southern hemisphere. Other than the male and spermathecal genitalia, their internal organization is poorly known. Here, we present results of our study of the ovaries and oogenesis in Insulodrilus bifidus, a phreodrilid from Western Australia using light and electron microscopy. The ovaries are paired and located in segment XII. They are inconspicuous and composed of several (10–12) spherical germ‐line cysts loosely interconnected by flattened somatic cells. The cysts usually comprise 32 germ cells and each cell is connected via a cytoplasmic bridge (ring canal) to the central cytoplasmic mass (the cytophore). In ovaries, germ cells in a given cyst develop in full synchrony. However, there is no synchrony among cysts, so there is a developmental gradient of cysts (from oogonial to early meiotic) along the longitudinal ovary axis. Within the cysts that are located in the distal end of the ovary the synchrony is finally lost and interconnected cells diversify into two morphologically distinct categories: an oocyte and 31 nurse cells. Such cysts detach from the ovaries and further development occurs within the body cavity. The oocyte gathers nutrients, mainly in form of yolk spheres, whereas nurse cells grow slightly and do not gather yolk. Organelles such as ribosomes, mitochondria and endoplasmic reticulum pass freely through the ring canals and are present within the cytophore, which suggests cytoplasmic transfer towards the oocyte. The formation of female germ‐line cysts equipped with cytophore and cells differentiated into oocyte and nurse cells matches the general pattern of oogenesis found in clitellates. In details, the ovary organization and oogenesis found in I. bifidus resembles the situation described in some representatives of Naidinae and Enchytraeidae.

中文翻译：

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phreodrilid clitellate 中卵巢组织和卵子发生的描述

Phreodrilidae 是一个小家族，由大约 50 种微小的淡水 clitellate 环节动物组成，主要栖息在南半球。除了男性和受精生殖器外，它们的内部组织鲜为人知。在这里，我们展示了我们使用光学和电子显微镜研究双歧双歧杆菌（一种来自西澳大利亚的 phreodrilid）卵巢和卵子发生的结果。卵巢是成对的，位于第 XII 段。它们不显眼，由几个（10-12）个球形生殖系包囊组成，通过扁平的体细胞松散地相互连接。囊肿通常包含 32 个生殖细胞，每个细胞通过细胞质桥（环管）与中央细胞质团块（细胞团）相连。在卵巢中，特定囊肿中的生殖细胞完全同步发育。然而，囊肿之间没有同步性，因此，沿卵巢纵轴存在囊肿的发育梯度（从卵原细胞到早期减数分裂）。在位于卵巢远端的囊肿内，同步性最终消失，相互连接的细胞分化为两个形态不同的类别：卵母细胞和 31 个护士细胞。这种囊肿从卵巢分离，并在体腔内进一步发展。卵母细胞主要以卵黄球的形式收集营养，而保育细胞生长缓慢，不收集卵黄。细胞器如核糖体、线粒体和内质网自由通过环管并存在于细胞胞内，这表明细胞质向卵母细胞转移。雌性生殖系囊肿的形成与细胞团和分化为卵母细胞和护士细胞的细胞相匹配，这与在阴蒂中发现的卵子发生的一般模式相匹配。详细地说，在双歧杆菌中发现的卵巢组织和卵子发生类似于 Naidinae 和 Enchytraeidae 的一些代表中描述的情况。