The deep-sea acorn worm Quatuoralisia malakhovi belongs to the phylum Hemichordata, class Enteropneusta, family Torquaratoridae, which was described in 2005. Owing to their epibenthic lifestyle and deep-sea habitat features, torquaratorids differ anatomically from shallow-water acorn worms; however, their morphology and fine structure are poorly studied. We have the opportunity to make three complete detailed series of histological sections of Q. malakhovi and to study the microscopic anatomy, histology and fine structure of the reproductive system of this acorn worm using scanning and transmission electron microscopy. The sexes of Q. malakhovi are separate and indistinguishable externally. The lobed testes occupy the dorsal side of the genital wings and distinctly bulge into the peribranchial cavity by their mature lobes. The central part of the testis is always submerged into the genital wing and opens via a single gonad pore. The monociliary muscle cells stretch along the external wall of the testis and surround the gonad pore, probably taking part in the contraction of the testis lobes for spawning. The germinative epithelium of the testis contains spermatogenic cells at different stages of development and interstitial cells. Yolk cells are not found. Interstitial cells embrace the spermatogonia and spermatogenic columns, providing horizontal compartmentalization of the germinative epithelium, and contain numerous phagosomes with remnants of degenerating spermatogenic cells. The testis wall contains haemal lacunae, which are usually located on the side opposite the gonad pore. We describe the fine structure of spermatogonia, spermatocytes clustered in spermatogenic columns, spermatids, and spermatozoa. Spermatozoa are of the ectaquasperm type and consist of an acorn-shaped head and a flagellum 18–25 µm long. The sperm head includes a beak-shaped acrosomal part, a spherical nucleus and a midpiece containing a ring of 5 or rarely 6 mitochondria. The male reproductive system and sperm structure of Q. malakhovi, a representative of the family Torquaratoridae, have a number of differences from shallow-water acorn worms; however, the spermatogenesis and sperm structure of Q. malakhovi generally follow the pattern of the other three enteropneust families, and the phylogenetic significance of these deviations should be the subject of further research.

中文翻译：

---

来自白令海的深海橡子蠕虫 Quatuoralisia malakhovi （Hemichordata， Enteropneusta， Torquaratoridae） 的雄性生殖系统


深海橡子蠕虫 Quatuoralisia malakhovi 属于 2005 年描述的 Enteropneusta 类 Orquaratoridae 门。由于其表层底栖生活方式和深海栖息地特征，torquaratorids 在解剖学上与浅水橡子蠕虫不同;然而，它们的形态和精细结构研究不足。我们有机会制作 Q. malakhovi 的三个完整详细的组织学切片系列，并使用扫描和透射电子显微镜研究这种橡子虫生殖系统的微观解剖学、组织学和精细结构。Q. malakhovi 的性别是独立的，在外部无法区分。裂片睾丸占据生殖器翅的背侧，并通过其成熟的裂片明显隆入鳃周腔。睾丸的中央部分总是浸没在生殖器翼中，并通过单个性腺孔打开。单纤毛肌细胞沿着睾丸外壁伸展并围绕性腺孔，可能参与睾丸叶的收缩以产卵。睾丸的生发上皮包含处于不同发育阶段的生精细胞和间质细胞。未发现卵黄细胞。间质细胞包含精原细胞和生精柱，提供生发上皮的水平区室化，并包含许多吞噬体和退化生精细胞的残余物。睾丸壁包含血腔，通常位于性腺孔对面的一侧。我们描述了精原细胞、聚集在精原柱中的精母细胞、精子细胞和精子的精细结构。 精子属于外生植物类型，由橡子形头部和 18-25 μm 长的鞭毛组成。精子头包括一个喙状顶体部分、一个球形核和一个包含一个 5 个或很少 6 个线粒体环的中段。栎属 Torquaratoridae 的代表，其雄性生殖系统和精子结构与浅水橡子蠕虫有许多不同之处;然而，Q. malakhovi 的精子发生和精子结构通常遵循其他 3 个肠系科的模式，这些偏差的系统发育意义应成为进一步研究的主题。