Kinorhynchs are marine microscopic invertebrates (so called meiobenthos), composing the phylum Kinorhyncha. They usually inhabit muddy, sandy, or silty sediment, and often also in interstices of sessile organisms (algae, sponges, etc.). Because of their habitat and their long body covered by hard exoskeleton as well as head with numerous spinous structures (= scalids) conjure an image of oriental dragons, they are called as “mud dragons” as English common name.
So far, about 300 kinorhynch species have been described from various marine environments and from shallow to the deep-sea waters all around the world, however, only eight species were reported from the cave environments. This small number of records is of course, not because of their rarity in caves, but because of scarcity of investigations for meiobenthos in general in the cave environments.
Yamasaki et al. (2020) investigated marine meiobenthos in the Daidokutsu submarine cave in Iejima, Okinawa, Japan, finding and describing three new kinorhynch species, Echinoderes gama
(Fig. 1A), E. kajiharai
and E. uozumii
Together with Ryuguderes iejimaensis
described also from the Daidokutsu cave in 2016, four out of eleven cave kinorhynchs (ca. 40%) have been from this cave. But again, this is just because the investigation on cave meiobenthos has been carried out scarcely, and that in the Daidokustu cave has been done relatively better. There should be much more undescribed mud dragons as well as other meiobenthic species waiting in cave sediment for their discovery.
It is not difficult to catch such microscopic meiobenthos, just collect sediment! But you need a microscope to see them. If you are interested in meiobenthos or if you have an opportunity to collect any sediment sample in a cave, ask meiobenthologists. It will probably lead to an interesting discovery!
Yamasaki, H.; Fujimoto, S.; Tanaka, H. (2020). Three new meiobenthic species from a submarine cave in Japan: Echinoderes gama
, E. kajiharai
and E. uozumii
(Kinorhyncha: Cyclorhagida). Journal of the Marine Biological Association of the United Kingdom. https://doi.org/10.1017/S0025315420000429