{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T21:52:31Z","timestamp":1791237151850,"version":"4.1.0"},"reference-count":47,"publisher":"Zoological Society of Japan","issue":"4","content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Zoological Science"],"published-print":{"date-parts":[[2026,5,6]]},"abstract":"<jats:p>Ultrastructural studies of oogenesis in Heterotardigrada are limited. Here, we examined the ovarian organization of Actinarctus doryphorus using transmission electron microscopy and three-dimensional reconstruction. Four female specimens at different developmental stages, including a juvenile, were analyzed. The ovary is a single sac-like structure dorsally above the digestive tract, partially supported by longitudinal dorsal muscles. Early germ cells form anterior clusters interconnected by cytoplasmic bridges. Previtellogenic oocytes contain numerous mitochondria clustered around a prominent nuage, suggesting a conserved role in piRNA-mediated genome protection. Vitellogenic oocytes occupy the posterior half of the ovary, with the posterior-most cell developing as the egg and the remaining cells functioning as nurse cells. Nurse cells form a syncytium, and ER-rich accessory cells at the periphery likely contribute to yolk and material transfer. Large aggregations of lysosome-rich vesicles in peripheral ovarian cells suggest apoptotic degeneration of trophocytes and ER-rich cells after completing their function. These findings reveal that A. doryphorus exhibits polytrophic meroistic oogenesis with syncytial nurse cells, ER-rich accessory cells, and nuage-containing previtellogenic oocytes. This study provides the first comprehensive description of oogenesis in a heterotardigrade and highlights conserved mechanisms for cytoplasmic and genomic support during gametogenesis, suggesting avenues for exploring the evolutionary diversification of reproductive strategies in tardigrades.<\/jats:p>","DOI":"10.2108\/zs260005","type":"journal-article","created":{"date-parts":[[2026,6,3]],"date-time":"2026-06-03T07:19:32Z","timestamp":1780471172000},"page":"374-387","source":"Crossref","is-referenced-by-count":0,"title":["Ultrastructure of Oogenesis in Actinarctus doryphorus (Heterotardigrada, Arthrotardigrada, Tanarctidae)"],"prefix":"10.2108","volume":"43","author":[{"given":"Atsushi C.","family":"Suzuki","sequence":"first","affiliation":[{"name":"Research and Education Center for Natural Sciences, Keio University, Hiyoshi, Yokohama 223-8521, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Reinhardt M\u00f8bjerg","family":"Kristensen","sequence":"additional","affiliation":[{"name":"Natural History Museum of Denmark, University of Copenhagen, Copenhagen, DK 2100 Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"848","reference":[{"key":"1","doi-asserted-by":"crossref","unstructured":"T Altiero, AC Suzuki, L Rebecchi,  \"Water Bears: The Biology of Tardigrades. 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J Murr. (Eutardigrada).\" 169 (1979)"},{"key":"45","unstructured":"B W\u0119glarska,  \"Proceedings of the Third International Symposium on Tardigrada.\"  \"Ultrastructural study of the formation of egg envelopes in Macrobiotus richtersi (Eutardigrada).\" 115 (1982)"},{"key":"46","doi-asserted-by":"crossref","unstructured":"B W\u0119glarska,  \"Zoomorphology.\"  107, \"Yolk formation in Isohypsibius (Eutardigrada).\" 287 (1987)","DOI":"10.1007\/BF00312174"},{"key":"47","doi-asserted-by":"crossref","unstructured":"S Yokota,  \"Acta Histochem Cytochem.\"  41, \"Historical survey on chromatoid body research.\" 65 (2008)","DOI":"10.1267\/ahc.08010"}],"container-title":["Zoological Science"],"original-title":[],"deposited":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T20:56:57Z","timestamp":1791233817000},"score":1,"resource":{"primary":{"URL":"https:\/\/bioone.org\/journals\/zoological-science\/volume-43\/issue-4\/zs260005\/Ultrastructure-of-Oogenesis-in-Actinarctus-doryphorus-Heterotardigrada-Arthrotardigrada-Tanarctidae\/10.2108\/zs260005.full"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,5,6]]},"references-count":47,"journal-issue":{"issue":"4","published-online":{"date-parts":[[2026,8,1]]}},"URL":"https:\/\/doi.org\/10.2108\/zs260005","relation":{},"ISSN":["0289-0003","2212-3830"],"issn-type":[{"value":"0289-0003","type":"print"},{"value":"2212-3830","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,5,6]]}}}