Thermozodium esakii Rahm, 1937
The Mesotardigrade
Taxonomy & Nomenclature
This taxon is accepted by (Guidetti et al., 2025), but they consider the class Mesotardigrada to be a nomen dubium. Grothman et al. (2017) considered both the species and the class to be nomina dubia.
Etymology
Grothman et al. (2017): "Rahm named T. esakii after Professor Dr. Esaki of Kyushu Imperial University (now Kyushu University) in Japan"
Conservation Status
Missing if valid
Last record: 1937 (Rahm, 1937a,b)
Grothman et al. (2017) state that the type locality has been unsuccessfully searched for the species.
Distribution & Habitat
near Nagasaki, Kyūshū, Japan
Type locality: "in the runoff from hot water springs in Unzen National Park (now Unzen-Amakusa National Park), Kyushu" (Grothman et al., 2017)
Nelson (2002:652) states that the type locality was destroyed in an earthquake, but Suzuki et al. (2017) report having visited hot springs within the Unzen—Amakusa National Park during May 2012 and May 2013. And Grothman et al. (2017) state:
"Attempts to study T. esakii are further complicated by the study area's proximity to an active volcano. It has been suggested that the area, including the spring sampled by Rahm, has been altered or destroyed since 1937 by earthquakes (Ramazzotti and Maucci, 1983; Nelson, 2002). However, we have found no evidence of such destruction of the site described by Rahm (1937c, d)... While the geologic activity in the Shimabara area has apparently not destroyed the aboveground locality, it may have altered the underground flow of spring water (Tabata, 1961), perhaps altering the ecology of Rahm's original sampling site. "
Biology & Ecology
Hypodigm
Today known only from a drawing of one individual (Grothman et al., 2017). It is not clear if any type specimens were ever preserved in the first place (Ibid.). Either way, no voucher specimens are known today (Nelson, 2002:652; Grothman et al., 2017; Suzuki et al., 2017).
Media
Today known only from a drawing of a single individual (Grothman et al., 2017).
References
Original scientific description:
Rahm, Gilbert. (1937a). Eine neue Tardigraden-Ordnung aus den heiβen Quellen von Unzen, Insel Kyushu, Japan. Zoologischer Anzeiger 120: 65-71.
Other references:
Fleming, James F. and Arakawa, Kazuharu. (2021). Systematics of tardigrada: A reanalysis of tardigrade taxonomy with specific reference to Guil et al. (2019). Zoologica Scripta 50(3): 376-382. https://doi.org/10.1111/zsc.12476
Grothman, Gary T., Johansson, Carl, Chilton, Glen, Kagoshima, Hiroshi, Tsujimoto, Megumu and Suzuki, Atsushi C. (2017). Gilbert Rahm and the Status of Mesotardigrada Rahm, 1937. Zoological Science 34(1): 5-10. https://doi.org/10.2108/zs160109
Guidetti, R., McInnes, S. J. and Kristensen, R. M. (2025). World List of Tardigrada. Thermozodium esakii Rahm, 1937. Accessed through: World Register of Marine Species at: https://www.marinespecies.org/aphia.php?p=taxdetails&id=343575 on 2025-05-17
Nelson, Diane R. (2002). Current Status of the Tardigrada: Evolution and Ecology. Integrative and Comparative Biology 42(3): 652-659. https://doi.org/10.1093/icb/42.3.652
Noda, Hirokuni. (1997). Does Thermozodium esakii Exist? Japanese Society of Systematic Zoology 2: 13-15. (in Japanese)
Okada, Y. and Ito, Y. (1938). Biological studies of thermal waters in Japan (XVI): Thermophilous animals in the Aso and Unzen National Parks. Jap. J. Limnol. 8: 361-370. (in Japanese with English abstract)
Rahm, Gilbert. (1937b). A new ordo of tardigrades from the hot springs of Japan (Furu-yu Section, Unzen). Annot. Zool. Japon 16(4): 345-352.
Ramazzotti, G. and Maucci, W. (1983). II phylum Tardigrada. 3rd ed. English translation by Beasley CW, 1995. Mem Ist Ital Idrobiol “Dott. Marco de Marchi” 41: 1-1014.
Suzuki, Atsushi C., Kagoshima, Hiroshi, Chilton, Glen, Grothman, Gary T., Johansson, Carl and Tsujimoto, Megumu. (2017). Meiofaunal Richness in Highly Acidic Hot Springs in Unzen-Amakusa National Park, Japan, Including the First Rediscovery Attempt for Mesotardigrada. Zoological Science 34(1): 11-17. https://doi.org/10.2108/zs160108
https://extinctanimals.proboards.com/thread/20306/thermozodium-esakii