The Synonymy of the Supratidal Crab Species Parasesarma cognatum Rahayu & Li, 2013 with P. liho Koller, Liu & Schubart, 2010 (Decapoda: Brachyura: Sesarmidae) Based on Morphological and Molecular Evidence, with a Note on P. paucitorum Rahayu & Ng, 2009

Minuca panema (Coelho, 1972): Resurrection of a Fiddler Crab Species from Brazil Closely Related to Minuca burgersi (Holthuis, 1967) (Crustacea, Decapoda, Brachyura, Ocypodidae)

We redescribe a species of fiddler crab, Minuca panema (Coelho, 1972), from the Atlantic coast of South America. It is closely related to M. mordax (Smith, 1870), and until now, the taxon has been considered to be synonymous with another closely related species Minuca burgersi (Holthuis, 1967). However, we found that two clades of M. burgersi sensu lato were restricted to the Caribbean Basin. This distribution differs from than that of M. panema, which occurs primarily along the eastern coast of South America, ranging from the island of Trinidad to Praia da Armação, Santa Catarina, Brazil. Based on our field studies, the geographical boundary between M. burgersi sensu stricto and M. panema is the Tobago Basin, north of Trinidad. Since the two species diverged only 3 to 4 million years ago, as dated from the phylogeny of the genus Minuca Bott 1954, there are few reliable morphological features that can be used to distinguish them clearly. In live crabs, there is a striking difference in coloration between the cherryred South American M. panema and the rusty-red Caribbean M. burgersi sensu lato. In males, the pattern of tubercles on the inner surface of the major cheliped varies between the two species. In females, the vulva is slightly larger in M. burgersi sensu stricto. Ocean tides and currents together with siltation owing to freshwater outflow from the Amazon and Orinoco rivers most likely have driven the divergence of these species. In the Caribbean, small tidal amplitudes have minimized long-distance gene flow in M. burgersi sensu stricto from isolated insular lagoons. In contrast, large tidal amplitudes and exposed habitats on riverbanks along the eastern Atlantic coast of South America have enabled long-distance dispersal in M. panema. DNA analysis reveals that haplotypes of cytochrome c oxidase subunit 1 are not shared between the species. Since natural selection and/or genetic drift have yet to produce extensive morphological divergences between M. panema and M. burgersi sensu stricto, we speculate that changes in the genes regulating mitochondrial DNA functions have led to speciation at the molecular level. According to the mitonuclear compatibility concept, we propose that mitochondrial DNA may be at the forefront of speciation events and that co-evolved mitonuclear interactions are responsible for some of the earliest genetic incompatibilities arising among isolated populations.

Taxonomy and Phylogeography of the Freshwater Crab Geothelphusa tawu Species Complex (Crustacea: Decapoda: Potamidae) from Southern Taiwan and Offshore Islets

The freshwater crabs Geothelphusa tawu Shy, Ng & Yu, 1994, G. lutao Shy, Ng & Yu, 1994 and G. lanyu Shy, Ng & Yu, 1994 from southern Taiwan and the offshore islets, Lyudao (Green I.) and Lanyu (Orchid I.) are closely related in morphology and genetics, and have been proposed to be the same species. Examination of a series of specimens collected from the distributional ranges of the three species indicated that key characters of the ambulatory legs and the male first gonopod (G1) are too variable to support the identity of three species. Based on the mitochondrial 16S rDNA and cytochrome oxidase subunit I (COI) sequences, the phylogenetic analysis did not recover three clades corresponding to the three species, but only a main clade without further clear grouping. The interspecific distances of nucleotides are also too small to support the species delimitation. We conclude that the three species should be treated as a single species. Additionally, unique haplotypes of COI have been found in Lyudao and Lanyu, which are hypothesized as two founder populations that colonized the islets from the Taiwan main island during glacial maxima.

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.

Diversity in the Taiwanese Swimming Crabs (Crustacea: Brachyura: Portunidae) Estimated through DNA Barcodes, with Descriptions of 14 New Records

The swimming crabs (family Portunidae) are distributed worldwide and commonly inhabit estuaries, mangroves, reefs, shallow and the deep sea. Previously, 75 species and 19 genera in this family were known to Taiwan. Our study examined specimens in Taiwanese waters, including the islands, collected between 2016 and 2020 or deposited in museums. Through the cytochrome oxidase subunit I DNA barcode marker and morphological examination, 71 species were identified. The minimum interspecific distances were greater than 4.09%, except in two unresolved groups: Charybdis miles (De Haan, 1835) and Ch. sagamiensis Parisi, 1916, as well as Thranita pelsarti (Montgomery, 1931) and Thr. prymna (Herbst, 1803). In addition, 14 species belonging to nine genera were confirmed as new records to Taiwan, viz. Carupa ohashii Takeda, 1993, Lupocyclus inaequalis (Walker, 1887), Luu. tugelae Barnard, 1950, Lupocycloporus minutus (Shen, 1937), Monomia gladiator (Fabricius, 1798), M. lucida Koch & Ďuriš, 2018, Podophthalmus minabensis Sakai, 1961, Thalamita gatavakensis Nobili, 1906, Tha. spinifera Borradaile, 1902, Thalamitoides quadridens A. Milne-Edwards, 1869, Tho. tridens A. Milne-Edwards, 1869, Thr. cerasma (Wee & Ng, 1995), Thr. coeruleipes (Hombron & Jacquinot, 1846) and Xiphonectes tuberculosus (A. Milne-Edwards, 1861). This study thus raises the total number of Portunidae species in Taiwan to 89.

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.

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

Three new coastal crabs, Parasesarma aurifrons n. sp., P. sanguimanus n. sp. and P. gemmatum n. sp. (Sesarmidae), are described from Taiwan and the Philippines. Parasesarma aurifrons is morphologically similar to P. ungulatum (H. Milne Edwards, 1853), P. liho Koller, Liu & Schubart, 2010, and P. obliquefrons (Rathbun, 1924); P. sanguimanus most closely resembles P. cricotus (Rahayu & Davie, 2002); and P. gemmatum is related to P. lenzii (De Man, 1895), but they can be distinguished by a suite of characters, including the structures of the chelipeds, gonopods and vulvae. The three new species are also supported by genetic data from the mitochondrial cytochrome oxidase subunit I (COI). Two species, P. lenzii and P. dumacense (Rathbun, 1914), are also recorded from Taiwan for the first time. The poorly known P. obliquefrons (Rathbun, 1924) from Samoa is figured for the first time as part of the comparisons and its taxonomically important gonopod structures are illustrated.

Description of the First Zoea of the Cavernicolous Crab Karstama boholano (Ng, 2002) (Crustacea: Decapoda: Sesarmidae) from Taiwan, with Notes on Ecology

This study presents a rare sesarmid cavernicolous crab, Karstama boholano (Ng, 2002), from Taiwan. This genus and species are both new to Taiwan. We describe the diagnostic characteristics of the Taiwanese specimen and provide illustrations of the adult and first zoea, as well as photographs of an adult in its natural habitat. The identity was confirmed by the COI gene sequence and morphological data. In addition, the zoeal morphology and breeding ecology of the genus Karstama Davie and Ng, 2007 are reported for the first time.