Osedax is a genus of siboglinid annelids in which the females live on dead vertebrate bones on the seafloor. These females have a posterior end that lies within the bone and contains the ovarian tissue, as well as the “roots” involved with bone degradation and nutrition. The males are microscopic and live as “harems” in the lumen of the gelatinous tube that surrounds the female trunk, well away from the ovary. Females are known to spawn fertilized primary oocytes, suggesting internal fertilization. However, little is known about sperm transfer, sperm storage, or the location of fertilization, and the morphology of the female reproductive system has not been described and compared with the reproductive systems of other siboglinids. A 3D-reconstruction of the ovisac of Osedax showed ovarian tissue with multiple lobes and mature oocytes stored in a “uterus” before being released through the single oviduct. The oviduct emerges as a gonopore on the trunk and travels along the trunk to finally open to the seawater as a thin cylindrical tube among the crown of palps. Light and transmission electron microscopy of mature Osedax sperm revealed elongate heads consisting of a nucleus with helical grooves occupied by mitochondria. In contrast to other Siboglinidae, Osedax sperm are not packaged into spermatophores or spermatozeugmata, and Osedax females lack a discrete region for sperm storage. Transmission electron microscopy and fluorescence microscopy allowed detection of sperm associated with ovarian tissue of the female ovisac of four different Osedax species. This provides the first evidence for the site of internal fertilization in Osedax. A heart body was found in the circulatory system, as seen in other siboglinids and some other annelids. The possible presence of nephridia in the anterior ovisac region was also documented. These morphological features provide new insights for comparing the regionalization of Osedax females in relation to other siboglinids.

中文翻译：

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Osedax（Annelida，Siboglinidae）的生殖系统：卵巢结构，精子超微结构和受精方式

Osedax 是 siboglinid 环节动物的一个属，其中雌性生活在海底的死脊椎动物骨头上。这些雌性的后端位于骨骼内并包含卵巢组织，以及与骨骼退化和营养有关的“根”。雄性是微观的，作为“后宫”生活在围绕着雌性躯干的胶状管腔中，远离卵巢。已知雌性会产生受精的原代卵母细胞，这表明内部受精。然而，人们对精子转移、精子储存或受精位置知之甚少，雌性生殖系统的形态也没有被描述和与其他 sibogliids 的生殖系统进行比较。Osedax 卵囊的 3D 重建显示具有多个叶的卵巢组织和成熟的卵母细胞储存在“子宫”中，然后通过单个输卵管释放。输卵管在树干上以生殖孔的形式出现，并沿着树干行进，最终在触须冠之间以细圆柱管的形式通向海水。成熟的 Osedax 精子的光学和透射电子显微镜显示细长的头部由一个核组成，螺旋槽被线粒体占据。与其他 Siboglinidae 相比，Osedax 的精子没有被包装到精囊或精子细胞中，并且 Osedax 雌性缺乏用于精子储存的离散区域。透射电子显微镜和荧光显微镜允许检测与四种不同 Osedax 物种的雌性卵囊的卵巢组织相关的精子。这为 Osedax 体内受精部位提供了第一个证据。在循环系统中发现了心脏体，如在其他 sibogliids 和一些其他环节动物中所见。还记录了前卵囊区域可能存在肾病。这些形态特征为比较 Osedax 雌性与其他 sibogliids 的区域化提供了新的见解。