Rie Tajiri

Two species of Rhabderemia, R. ginamaensis sp. nov. and R. forcipula (Lévi & Lévi, 1989), are reported from submarine anchialine caves of the Ryukyu Islands, Japan. Rhabderemia ginamaensis sp. nov., collected from the submarine cave of Ginama, Okinawa Island, differs from other congeners by its thinly encrusting morphology and the presence of microxea. Rhabderemia forcipula (Lévi & Lévi, 1989), once collected from the mesophotic zone of the Philippine Sea, was rediscovered for the first time since its original description in the dark nearshore submarine cave of Shimoji Island, Miyako Island Group. The species is characterized by a plumo-reticulate skeleton and spiculation: rhabdostyles, rugose microstyles, and sigmoid microscleres in two size classes, the larger ones being spirosigma and thraustosigma. A redescription of the type specimen and a detailed description of the newly collected specimens are provided to understand the morphological variation of the spicules, and to confirm the conspecificity of the type specimen and the submarine cave specimens. The two species, R. ginamaensis sp. nov. and R. forcipula are a new record of Rhabderemia and the family Rhabderemiidae from Japan, and the first report of Rhabderemia from submarine anchialine caves in the Indo-West Pacific. In addition, R. forcipula is the first species of the genus to be found from both a submarine cave and a mesophotic zone in the Indo-West Pacific.

Calcium oxalate kidney stones, the most prevalent type of kidney stones, undergo a multi-step process of crystal nucleation, growth, aggregation, and secondary transition. The secondary transition has been rather overlooked, and thus, the effects on the disease and the underlying mechanism remain unclear. Here, we show, by periodic micro-CT images of human kidney stones in an ex vivo incubation experiment, that the growth of porous aggregates of calcium oxalate dihydrate (COD) crystals triggers the hardening of the kidney stones that causes difficulty in lithotripsy of kidney stone disease in the secondary transition. This hardening was caused by the internal nucleation and growth of precise calcium oxalate monohydrate (COM) crystals from isolated urine in which the calcium oxalate concentrations decreased by the growth of COD in closed grain boundaries of COD aggregate kidney stones. Reducing the calcium oxalate concentrations in urine is regarded as a typical approach for avoiding the recurrence. However, our results revealed that the decrease of the concentrations in closed microenvironments conversely promotes the transition of the COD aggregates into hard COM aggregates. We anticipate that the suppression of the secondary transition has the potential to manage the deterioration of kidney stone disease.