SummaryMating behaviours for two species of dioecious eutardigrades: a strain of Paramacrobiotus sp. and Macrobiotus shonaicus (Stec et al., 2018) have been recorded previously, and observations have indicated that spermatozoa of both species are first released into the environment, then swim through the cloaca of the females and into the spermatheca. The fusion of gamete nuclei has not yet occurred in a laid egg. Therefore, it has been suggested that fertilization is completed externally as the egg is released into the environment before the nuclei of the gametes fuse. In the present study, the spermatozoa of both Paramacrobiotus sp. and M. shonaicus spermatozoa underwent morphological changes during reproduction. In morphometrical analyses of testicular spermatozoa, the tail, mid-piece, nucleus, and acrosome were significantly longer in Paramacrobiotus sp. compared with M. shonaicus. The nuclei of both the testicular and spermathecal spermatozoa were equally coiled, but the latter had shorter tails in both species. These spermatozoa were present on the surface of the egg chorion after oviposition. The tip of the acrosomes lay buried in the chorion, suggesting that penetration had occurred. We also proposed that the reduced tail is a conserved trait, at least in Macrobiotidae.

中文翻译：

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繁殖过程中精子形态的变化和首次观察到两种雌雄异株的巨型生物（Tardigrada：Eutardigrada）的顶体接触

摘要两种雌雄异株的 eutardigrades 的交配行为：一种副食肉动物sp。和长生菌（科技等人., 2018) 之前有记录，观察表明这两个物种的精子首先被释放到环境中，然后游过雌性的泄殖腔并进入受精囊。配子核的融合尚未在产卵中发生。因此，有人建议在配子核融合之前将卵子释放到环境中，从而在外部完成受精。在本研究中，两者的精子副食肉动物sp。和米.shonaicus精子在繁殖过程中经历了形态变化。在睾丸精子的形态计量学分析中，尾部、中段、核和顶体显着较长。副食肉动物sp。和....相比米.shonaicus. 睾丸和精囊精子的细胞核同样卷曲，但后者在两个物种中都有较短的尾巴。这些精子在产卵后存在于卵子绒毛膜的表面。顶体的尖端埋在绒毛膜中，表明发生了穿透。我们还提出减少的尾巴是一种保守的特征，至少在 Macrobiotidae 中是这样。