This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers have identified two new species in the genus Bogidiella, small shrimp-like amphipods that live in subterranean aquatic environments, from cave waters on the Ryukyu Islands, a subtropical island chain in southwestern Japan. These creatures are clear products of their underground aquatic environment, often lacking pigmentation and eyes, with elongated appendages and reduced swimming legs, called pleopods.
Hiroshima University Professor Ko Tomikawa of the Graduate School of Humanities and Social Sciences and his collaborators describe the two amphipod species previously unknown to science in a study published in Zootaxa. Amphipods, specifically those in the family Bogidiellidae, can be found in often-overlooked environments, such as narrow connecting waterways and groundwater. These aquatic habitats also vary widely, from freshwater and brackish water to seawater-influenced systems such as anchialine waters, which are connected to the ocean through underground passages.
The new species in this study are Bogidiella isajii and Bogidiella painushima. B. isajii was collected from an anchialine undersea cave on Minamidaito Island, while B. painushima was found in freshwater flowing through a cave on Ishigaki Island. Cave waters like these are closely tied to groundwater environments, which can support specialized life adapted to darkness.
"Groundwater has long been used in human life as a source of drinking water and for agricultural purposes, but in recent years, the conservation of the groundwater environment has become a major challenge," said Tomikawa, corresponding author of the study. B. isajii is named after Yoshitaka Isajii, its discoverer. Specimens of the species measure approximately 3.8–4.3 mm long, about the size of a sesame seed.
The species is described as lacking the inner ramus, a branch-like appendage on its pleopods. Typically, amphipods have three pairs of pleopods, each with two branches. The rami armature (hardened structure of the exoskeleton; provides shape and utility) of the uropods ("legs" closest to the rear of the animal) in pairs 1 and 2 is also absent.
Additionally, the telson, or what most people know as the fan-like structure on a shrimp's tail (though in these species it is more of a flap), has a different shape than in other members of the genus and appears to be wider than it is long. The telson is generally useful in distinguishing amphipod species. B. painushima's name is derived from "Painu-shima," an Okinawan term meaning "southern island." Specimens of the species measure approximately 1.4–3.2 mm long, making them slightly smaller than B. isajii.
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