Germ cell cluster organization and oogenesis in the tardigrade Dactylobiotus parthenogeneticus Bertolani, 1982 (Eutardigrada, Murrayidae)

Abstract

Germ cell cluster organization and the process of oogenesis in Dactylobiotus parthenogeneticus have been described using transmission electron microscopy and light microscopy. The reproductive system of D. parthenogeneticus is composed of a single, sac-like, meroistic ovary and a single oviduct that opens into the cloaca. Two zones can be distinguished in the ovary: a small germarium that is filled with oogonia and a vitellarium that is filled with germ cell clusters. The germ cell cluster, which has the form of a modified rosette, consists of eight cells that are interconnected by stable cytoplasmic bridges. The cell that has the highest number of stable cytoplasmic bridges (four bridges) finally develops into the oocyte, while the remaining cells become trophocytes. Vitellogenesis of a mixed type occurs in D. parthenogeneticus. One part of the yolk material is produced inside the oocyte (autosynthesis), while the second part is synthesized in the trophocytes and transported to the oocyte through the cytoplasmic bridges. The eggs are covered with two envelopes: a thin vitelline envelope and a three-layered chorion. The surface of the chorion forms small conical processes, the shape of which is characteristic for the species that was examined. In our paper, we present the first report on the rosette type of germ cell clusters in Parachela.

Description of ovary organization and oogenesis in a phreodrilid clitellate

“…During spermatogenesis, cysts are formed as a rule in the majority of the taxa studied including annelids (Olive, ; Jamieson, , ; Ferraguti, ). In females, germ‐line cysts are found only in some taxa as, for example, arthropods (reviewed in Telfer, ; Büning, ; Bilinski, Kubiak & Kloc, ), tardigrades (Poprawa, Hyra & Rost‐Roszkowska, ; Poprawa & Janelt, ), nematodes (Wolke, Jezuit & Priess, ; Amini et al, ; Seidel et al, ), some annelids (Anderson & Huebner, ; Eckelbarger, ; Brubacher & Huebner, ; Urbisz et al, ) and certain vertebrates (e.g., Kloc, Biliński, Dougherty, Brey & Etkin, ; Lei & Spradling, ; Żelazowska & Fopp‐Bayat, ). When the cysts are already formed, they may function in two modalities.…”

Body cavity cells of Parachela during their active life

“…During oogenesis, the accumulation of the reserve material (yolk) in the cytoplasm of the oocyte (future egg) occurs. In tardigrades, the precursors of yolk are primarily synthesized by the oocyte and the trophocytes, which are sister cells of the oocytes (they originate from the germ line; Węglarska, , ; Poprawa, ; Poprawa et al ., ; Poprawa, Hyra & Rost‐Roszkowska, ; Poprawa et al ., ). Additionally, the cells of the midgut epithelium can participate in the synthesis of vitellogenins.…”

X-ray imaging of a water bear offers a new look at tardigrade internal anatomy

“…While the ligaments are generally presented in the literature as isolated within the body cavity [28], the right ligament in our scans appears closely associated with the midgut wall. Whether the ovary always occupies the space to the left of the midgut or whether this position varies between tardigrades has, to our knowledge, never been addressed, as the position of the ovary is usually described simply as “dorsal” or overlying the midgut [28]. Future studies using nanoCT may also aim to quantify exactly how the volume of the ovary changes throughout the reproductive cycle.…”