How is a giant sperm ejaculated? Anatomy and function of the sperm pump, or “Zenker organ,” in Pseudocandona marchica (Crustacea, Ostracoda, Candonidae)

Abstract

'Giant sperm', in terms of exceptionally long spermatozoa, occur in a variety of taxa in the animal kingdom, predominantly in arthropod groups, but also in flatworms, mollusks, and others. In some freshwater ostracods (Cypridoidea), filamentous sperm cells reach up to ten times the animal's body length; nonetheless, during a single copulation several dozen sperm cells can be transferred to the female's seminal receptacle. This highly effective ejaculation has traditionally been credited to a chitinous-muscular structure within the seminal duct, which has been interpreted as a sperm pump. We investigated this organ, also known as the Zenker organ, of a cypridoid ostracod, Pseudocandona marchica, utilizing light and electron microscope techniques and produced a three-dimensional reconstruction based on serial semi-thin histological sections. This paper shows that numerous muscle fibers surround the central tube of the Zenker organ, running in parallel with the central tube and that a thin cellular layer underlies the muscular layer. A cellular inner tube exists inside the central tube. A chitinous-cellular structure at the entrance of the organ has been recognized as an ejaculatory valve. In male specimens during copulation, we confirmed a small hole derived from the passage of a single spermatozoon through the valve. The new data allowed for proposing a detailed course of operation of the Zenker organ during giant sperm ejaculation.

Morphological and molecular diversity of Lake Baikal candonid ostracods, with description of a new genus

“…The Zenker organ has a balloon-like anterior end, a characteristic which has been noted in Pseudocandona inaequivalvis baikalensis Bronstein, 1947, some Undulacandona species (see Smith 2011; Karanovicand Cho 2017), and in the families Cyclocyprididae and Paracyprididae (see Danielopol 1982). The morphology and development of the Zenker organ has been studied recently (see Yamada and Matzke-Karasz 2012; Yamada et al 2014). The phylogenetic importance of its morphology is recognized on the higher taxonomic levels (Danielopol 1978; Matzke-Karasz 1997), but not well understood at the generic or even family level.…”

Subcellular preservation in giant ostracod sperm from an early Miocene cave deposit in Australia

“…Four males (QMF56080, QMF56093, QMF56099 and QMF57302) were identified by the presence of sperm pumps (Zenker organs) [23,24], preserved as tubular voids that are lined by an annulated wall and surrounded by radial spines typical of the group (figure 2; electronic supplementary material, videos S1 and S2). Four other specimens each have paired female seminal receptacles preserved (QMF54756, QMF56081, QMF56094 and QMF56098), including one female N. mckenziana (figure 3; electronic supplementary material, video S3) with almost pristinely preserved clews of the seminal ducts leading from the vaginas to the inflated seminal receptacles (figure 3; electronic Fossil spermatozoa of different preservation quality were found in one male (QMF56080) and three female H. collaris (QMF56081, QMF56094 and QMF56098), and one female N. mckenziana (QMF54756) (electronic supplementary material, videos S5 and S6).…”

Structural specialities, curiosities and record-breaking features of crustacean reproduction

“…Other well-preserved reproductive structures in the male were the paired Zenker organs (Fig. 11E, F), which are chitinous and muscular pumps that help to transfer the sperm into the female (Yamada and Matzke-Karasz, 2012).…”