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An assessment of the global freshwater crab diversity is presented. A total of 1,476 species in 14 families are currently known from all zoogeographical regions (except Antarctica), including 1,306 species in eight exclusively freshwater families (Pseudothelphusidae, Trichodactylidae, Potamonautidae, Deckeniidae, Platythelphusidae, Potamidae, Gecarcinucidae and Parathelphusidae). Estimates of true freshwater crab diversity including likely numbers of undescribed taxa suggest that the field remains largely in a “discovery” phase. Main ideas on the origins, diversification, and phylogeny of true freshwater crabs are briefly discussed. The economic importance of freshwater crabs is also highlighted.

In this study, the authors first obtained the mitochondrial genome of Somanniathelphusa boyangensis. The results showed that the mitochondrial genome is 17,032bp in length, included 13 protein-coding genes, 2 rRNAs genes, 22 tRNAs genes and 1 putative control region, and it has the characteristics of the metazoan mitochondrial genome A+T bias. All tRNA genes display the typical clover-leaf secondary structure except tRNASer(AGN), which has lost the dihydroxyuridine arm. The GenBank database contains the mitochondrial genomes of representatives of approximately 22 families of Brachyura, comprising 56 species, including 4 species of freshwater crab. The authors established the phylogenetic relationships using the maximum likelihood and Bayesian inference methods. The phylogenetic relationship indicated that the molecular taxonomy of S. boyangensis is consistent with current morphological classification, and Parathelphusidae and Potamidae are derived within the freshwater clade or as part of it. In addition, the authors used the COX1 sequence of Somanniathelphusa in GenBank and the COX1 sequence of S. boyangensis to estimated the divergence time of this genus. The result displayed that the divergence time of Somanniathelphusa qiongshanensis is consistent with the separation of Hainan Island from mainland China in the Beibu Gulf, and the divergence time for Somanniathelphusa taiwanensis and Somanniathelphusa amoyensis is consistent with the separation of Taiwan Province from Mainland China at Fujian Province. These data indicate that geologic events influenced speciation of the genus Somanniathelphusa.

A water quality assessment in the Saluran Tarum Barat was conducted at three stations, representing the beginning, middle, and end of the canal between February and May 2017. This research aimed to determine the quality of Saluran Tarum Barat water using benthic macroinvertebrates as a bioindicator through the Biological Monitoring Working Party-Average Score Per Taxon (BMWP - ASPT) method. Environmental parameters were also measured. The sampling found six families of macroinvertebrates: Naucoridae; Viviparidae; Parathelphusidae; Pisauridae; Palaemonidae; and Thiaridae. However, Parathelphusidae and Pisauridae families are not covered in the BMWP scoring list. Saluran Tarum Barat has an ASPT range from 4.25-4.5, which indicates that the water is moderately polluted.

Two new troglobitic species of the freshwater crab genus Sundathelphusa (Parathelphusidae), S. waray, n. sp., and S. lobo, n. sp., are described from two caves in Samar, Philippines. This discovery brings the number of cavernicolous species of Sundathelphusa in the Philippines to nine. It is the first record of freshwater and true cavernicolous crab species from Samar. These two new species are morphologically closely related to S. cavernicola Takeda, 1983 and S. hades Takeda and Ng, 2001, but differ distinctly in the shape of carapace and the presence of long corneous spines in the dactyli. The new species are characterized by the non-pigmented body, greatly reduced eyes and long ambulatory legs that are associated with previously known troglobitic crabs. The presence of corneous spines on the distal two segments of the ambulatory legs is suggested as troglomorphic adaptation to subterranean habitat. A key to the cavernicolous freshwater crabs of the Philippines is also provided.

Twenty-six species of freshwater shrimps and crabs, belonging to 14 genera of four families (Atyidae, Palaemonidae, Parathelphusidae, and Grapsidae) are reported from Halmahera, Indonesia. Of them, 10 are new records for the island while one species of Macrobrachium is here described as new. Description for new species, diagnoses for poorly known species, and taxonomic discussions for all species are provided.