Three New Species and Two New Records of Parasesarma De Man, 1895 (Crustacea: Brachyura: Sesarmidae) from Taiwan and the Philippines from Morphological and Molecular Evidence

Multigene Phylogenies of the Estuarine Sesarmid Parasesarma bidens Species Complex (Decapoda: Brachyura: Sesarmidae), with Description of Three New Species

S Parasesarma bidens (De Haan, 1835) is a common intertidal sesarmid crab that inhabits the estuarine and mangrove regions of East Asia, as well as Vietnam and the Philippines. Previous studies have suggested that P. bidens is a species complex composed of several species. Our findings indicated that the P. bidens species complex is monophyletic with six clades, as shown by reconstructed phylogenies based on mitochondrial 16S rDNA and cytochrome c oxidase subunit I, as well as nuclear 28S rDNA. Specimens of each clade exhibited different characters, including the morphology of the cheliped, anterior carapace, male gonopod 1, and female vulvae, as well as the coloration. Three species in this complex have been previously described: P. bidens (De Haan, 1835), P. cricotum (Rahayu & Davie, 2002), and P. sanguimanus Li, Shih & Ng, 2019. Here, we describe three additional species: P. continentale n. sp., P. insulare n. sp., and P. chiahsiang n. sp. Biogeographically, the range of P. bidens includes the southern margin of Korea, the main islands of Japan, and the Ryukyus, with a comparatively northern distribution. P. continentale is widely distributed from the continental coasts of southeastern and southern China (including northern Hainan Island) to southern Vietnam and is occasionally found in Penghu, Taiwan. Parasesarma insulare is an insular species distributed from Taiwan main island, the central Philippines, to northern Borneo. Finally, P. chiahsiang is mainly limited to the Penghu Islands (Pescadores) but is also sometimes found in Taiwan main island and the offshore Gueishan Island.

The role of anthropogenic disturbance and invasion of yellow crazy ant in a recent decline of land crab population

The yellow crazy ant, Anoplolepis gracilipes was first reported in Kenting National Park, Taiwan, in the 2000s, raising the concern of this invasive ant's potential effects on the native land crab populations. We investigated the distribution and abundance of A. gracilipes and its adverse effect on the land crab populations at four land crab hotspots within the park. Our survey results indicated that A. gracilipes was widespread and abundant at three of the study sites (Hsiangchiaowan, Shadao, and Natural Spring), while the distribution was much more confined at the fourth site (Houwan). Land crab populations experienced a notable decline at all the study sites except Houwan, indicating an inverse relationship between the population of land crabs and distribution/abundance of A. gracilipes. Combining the results of visual observations, the decline of land crab populations can be attributed, at least partially, to direct attacks by A. gracilipes on land crabs in their natural habitat and during the breeding migration season. Generalized additive model showed that worker abundance of this ant is associated with human disturbance levels, suggesting that anthropogenic disturbance may have contributed to the decline in land crab populations via promoting the abundance of A. gracilipes.

The Taiwanese and Philippine Species of the Terrestrial Crabs Bresedium Serène and Soh, 1970 and Sesarmops Serène and Soh, 1970 (Crustacea: Decapoda: Brachyura), with Descriptions of Two New Species

The genera Bresedium Serène and Soh, 1970 and Sesarmops Serène and Soh, 1970 are two closely related taxa inhabiting terrestrial or freshwater environments from the Indo-West Pacific. Based on morphological and molecular evidence, two new species from Taiwan, the Philippines and Indonesia are described in this study, viz. B. eurypleon n. sp. and S. mora n. sp. The new species can be distinguished from congeners by a suite of carapace, chelipedal, gonopodal and vulvar characters. Bresedium philippinense (Rathbun, 1914) is here shown to be a junior synonym of B. brevipes (De Man, 1889). A poorly known Philippine species, Sesarmops mindanaoensis (Rathbun, 1914), is redescribed from the type and fresh material, and is recorded for the first time from Taiwan.

Diversity of Taiwanese Brackish Crabs Genus Ptychognathus Stimpson, 1858 (Crustacea: Brachyura: Varunidae) based on DNA Barcodes, with Descriptions of Two New Species

Species in the brackish crab genus Ptychognathus are common in the seashore and estuary habitats with freshwater input. Due to their similar morphologies and dull colorations, it is always difficult to distinguish the species in this genus. In this study, the DNA barcode gene COI (cytochrome c oxidase subunit I) was used to help identify Ptychognathus from Taiwan. The results showed that the 10 species can be identified successfully based on COI, with intraspecific distances below 1.54% and interspecific distances of 12.2%-19.57%. In addition, two new species of Ptychognathus are described from Taiwan. Ptychognathus makii sp. nov. from southern Taiwan is similar to P. altimanus (Rathbun, 1914), and P. stimpsoni sp. nov. from southern Taiwan and the southern Philippines resembles P. aff. barbatus (A. Milne-Edwards, 1873) and P. pusillus Heller, 1865. Both species can be distinguished from other congeners by a suite of characters, including the carapace, orbital region, frontal region, telson of male pleon, male first gonopod, and setae on ambulatory legs.

Comparative Mitochondrial Genome Analyses of Sesarmid and Other Brachyuran Crabs Reveal Gene Rearrangements and Phylogeny

Mitochondrial genomes (mitogenomes) are important for understanding molecular evolution and phylogenetic relationships. The complete mitogenome of Perisesarma bidens was determined, which is 15,641 bp in length. The A + T content of P. bidens mitogenome was 74.81%. The AT skew was slightly negative (-0.021). The 22 tRNAs ranged from 65 to 73 bp and were highly A + T biased. All tRNA genes had typical cloverleaf structures, except for the trnS1 gene, which lacked a dihydrouridine (DHU) arm. The gene order within the P. bidens mitogenome was identical to the pancrustacean ground pattern, except for the translocation of the trnH. Additionally, the gene order of trnI-trnQ-trnM in pancrustacean ground pattern became trnQ-trnI-trnM in P. bidens. Phylogenetic analyses supported the inclusion of P. bidens in Sesarmidae and the promotion of Sesarminae to Sesarmidae. The results will help us to better understand the status and evolutionary history of Grapsoidea crabs.

What is Sesarmops impressus (H. Milne Edwards, 1837) (Crustacea: Brachyura: Sesarmidae)?

The identity of the widely distributed mangrove and riverine sesarmid crab Sesarmops impressus (H. Milne Edwards, 1837) is clarified. The species has been reported from Madagascar to the South Pacific, but its taxonomy was previously confused. On the basis of morphological characters and available molecular evidence (using 16S rDNA and cytochrome oxidase subunit I), Sesarmops impressus is restricted to the western Indian Ocean and S. frontale A. Milne-Edwards, 1869 is confirmed to be its junior synonym. Sesarmops similis (Hess, 1865), long synonymised under S. impressus, is here recognised as a separate species and a neotype from Samoa is designated. The identity of the poorly known S. atrorubens (Hess, 1865), which has often been confused with S. impressus, is also clarified, and a neotype is selected from Fiji. Specimens from the eastern Indian Ocean and western Pacific are here identified as two new species, S. indicus sp. nov. and S. imperator sp. nov.