During 21 to 23 September 2017, the 88th annual meeting of the Zoological Society of Japan was held in Toyama prefecture. As one symposium of it on 21 September 2017, the Japanese Society of Systematic Zoology Symposium 2017 entitled ‘Evolutionary traits of arthropods toward extreme environments: Dangerous reality for taxonomists in the study field' was conducted at Toyama Prefectural Civic Center (Toyama City, Toyama Prefecture). The five interesting lectures were given by the special invited speakers: Satoshi Shimano ‘Strategy of mites for maintaining diversity’, Taizo Nakamori & Seikoh Saitoh ‘DNA barcoding and community analyses using next-generation sequencing in Collembola’, Shimpei F. Hiruta ‘Terrestrial ostracods’, Yoshihisa Fujita ‘Crustacean fauna in submarine and anchialine caves of the Ryukyu Islands’ and Takashi Komatsu ‘Diversity of Japanese troglobiontic arthropods’.

The taxon-group of Acari has most number of valid species (almost 55,000) in Arachnida, however Acari was disappeared in textbooks of invertebrate nowadays. Acariformes and Parasitiformes sensu lato are used as separated taxon-groups instead of Acari. Although two-name system, tick (sucking blood) and mite (others) were common for meaning Acari in some countries, Japanese use one word “dani” for Acari. French use three categories, tick, mite and ciron (ceron). The “ciron” means cheese mites (and some small bugs) and was used as the symbol of minimums in some French literature (e.g. Fables by Jean de la Fontaine in 1668, Pensées by Blaise Pascal in 1670). Acarine species are recorded almost 2,000 in Japan, and 1% (almost 20 species) of them are harmful as common sucking blood ticks. Acari have diverse eating habits, while other members of Arachnida are only predators. The diversity of Acarine eating habits may have maintained species diversity of them. Oribatida as a decomposer has various physical appearance. The much morphological diversity is a strategy to defend against predators. The oribatid mite have not only morphological defense but also chemical defense as chemical secretion from opisthonotal glands and physical defense as jumping. These various defense strategies are also helpful in maintaining diverse species.

Recent studies of decapod crustaceans in anchialine and submarine caves of the Ryukyu Islands were reviewed. A total of 10 species, belonging to 7 genera of 5 families, have been recorded in anchialine caves, and all of them are listed on the Red List (List of Endangered and Threatened Species in Japan or Okinawa Prefecture). In the submarine caves, remarkable findings of decapods and other crustaceans are continuing even in recent years. Further “many eyes” will be poured into the submarine caves, it is expected that the characteristics of the animal communities in the Ryukyu Islands will be understood in more detail.

Collembola, also called springtails, are wingless microarthropods that are widespread in terrestrial habitats and mainly inhabit soil. Applications of collembolan DNA barcoding are expected in taxonomy, ecology, and environmental sciences to unveil cryptic diversity, to provide a rapid and easy method for community measurements, and to provide an accurate identification method for ecotoxicological test species for non-taxonomists. Collembolan DNA barcoding was initiated in 2004 with Canadian specimens and is now ongoing in several countries. A rapid method for non-destructive DNA extraction from individual specimens has been developed to preserve voucher specimens. A quantitative protocol for Collembola DNA metabarcoding has also been developed. Collembolan DNA barcode data are gradually accumulating, although data on type specimens and topotypes are still scarce. Because several cryptic lineages have been found through DNA barcoding, taxonomists who can classify cryptic lineages and describe cryptic species are needed.

Ostracods are small aquatic crustaceans with a calcified, dorsally hinged bivalve-like carapace that can enclose the body entirely. They are distributed almost every aquatic environment, such as shallow to deep pelagic environments, freshwater, brackish-water, and also subsurface-water. However, there are several lineages of podocopid ostracods that have been reported from semi- or fully terrestrial habitats. While reports of such terrestrial ostracods are scarce, to date, four species from three genera are known in Japan. These terrestrial ostracods had been treated as endemic to each region. However, recent studies suggest that their dispersal abilities have been underestimated. It is clear that further investigations on the terrestrial environments around the world would drastically change the views of diversity and distribution of terrestrial ostracods.

There are many rock grike of various sizes under the ground. Recent studies have revealed that the grike is habitat for troglobiontic organisms that are extremely specialized to live within it. In this paper, focused on troglobiontic arthropods in Japan, the diversity of the species is discussed, together with a threat to their survival.

Leptoseris amitoriensis Veron, 1990 is recorded on the basis of specimens from the southern coast of Amami-oshima Island, Kagoshima, Japan. The colonies of L. amitoriensis was found on the bottom edge of a sandy slope at 31 m depth in Atetsu Bay, Oshima Strait. The paratypes examined in this study (CMNH-ZG 08451, RUMF-ZG-04388 and RUMF-ZG-04389: collected by one of the author of this study) appear to make up the entire type series to the exception of the holotype. The feature that corallite rims are slightly raised compared to the coenosteum was observed in both the specimens in this study and the paratypes, and this is considered to be an additional diagnostic character of this species. This report represents the northernmost record of this species and the second record in Japan.

Six specimens (39.9–81.4 mm standard length) of the Round Scorpionfish Neomerinthe erostris (Alcock, 1896) (Scorpaenidae), previously recorded from the Indo-West Pacific and in the western Pacific from Taiwan to New Caledonia and the Wallis and Futuna Islands, were collected from Uchinoura Bay, Osumi Peninsula; southern Okinawa Trough; and Iriomote Island, Yaeyama Islands, southern Japan. The six specimens represent the first records of N. erostris from Japanese waters and include the northernmost records (Uchinoura Bay) for the species. The Japanese specimens are described here in detail and the new Japanese name “Yabusame-kasago” is proposed for the species.