Morphological and Molecular Evidence for the Identity of Two Land Hermit Crabs Coenobita longitarsis De Man, 1902 and C. pseudorugosus Nakasone, 1988 (Crustacea: Decapoda: Anomura: Coenobitidae).

Two species of land hermit crabs, Coenobita longitarsis De Man, 1902 and C. pseudorugosus Nakasone, 1988 were described based on female specimens from Maluku, Indonesia and specimens from Cebu, the Philippines, respectively. However, no confirmed records of either species have been reported since their original descriptions. In this study, we examined specimens with typical morphological characters of C. longitarsis from Papua New Guinea and C. pseudorugosus from the Philippines and Indonesia, further supported by the analyses of the DNA barcoding marker, cytochrome oxidase subunit I (COI). The characters of male C. longitarsis are provided for the first time, with coxae of male fifth pereiopods subequal, without sexual tubes developed. Their slender morphology is suggested to be an adaptation to utilize native terrestrial snail shells in inland forests, which may also explain its rarity. Coenobita pseudorugosus is very similar to C. rugosus H. Milne Edwards, 1837, but can be distinguished by the adult sizes, as well as the morphology of sexual tubes of male fifth pereiopods and propodus of left third pereiopod. Morphological variation and the fresh coloration of C. longitarsis and C. pseudorugosus are also provided in this study.

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.

Molecular evidence and differences in gonopod morphology lead to the recognition of a new species of the freshwater crab genus Candidiopotamon Bott, 1967 (Crustacea, Brachyura, Potamidae) from eastern Taiwan.

A new freshwater crab of the potamid genus Candidiopotamon Bott, 1967, is described from eastern Taiwan. Candidiopotamonpenglai sp. nov. is morphologically similar to C.rathbuni (De Man, 1914) from western Taiwan, but can be distinguished by the morphology of the male first gonopod (G1), as well as by their mitochondrial DNA (16S rRNA and COI genes). In the G1 of C.rathbuni, the subterminal segment shows a cline from robust in northern populations to slender in southern populations. In the G1 of C.penglaisp. nov., a distinctly larger and more distally directed keel-like projection is found on the distal inner edge of the terminal segment, with northern populations having an inward-curving subterminal segment and southern populations a straight subterminal segment. The genetic differentiation of the two species of Candidiopotamon within Taiwan is discussed, and morphological differences are compared. A key to the species of Candidiopotamon is also provided.

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.

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.

Tuerkayana latens, a New Species of Land Crab from French Polynesia, with a Discussion on the Phylogeny of the Genus (Crustacea: Decapoda: Brachyura: Gecarcinidae).

The taxonomy of the gecarcinid land crab Tuerkayana rotundum (Quoy & Gaimard, 1824) is revised. The taxon, the type species of the genus, occurs from the western Indian Ocean to the western Pacific, and varies substantially in colour and various morphological features, but the male first gonopod structure is constant and the extensive genetic data from mitochondrial 16S rDNA, cytochrome c oxidase subunit 1 and control region markers confirms the recognition of one wide-ranging species. Specimens from Tuamotu in French Polynesia and Pitcairn Island, however, differ in having a smoother and slightly more swollen carapace, and significantly, the male first gonopod structure is distinctly different. The genetic data also supports their differentiation. As such, this material is here recognised as a new species, Tuerkayana latens n. sp.

The Complete Mitogenome of Xeruca formosensis (Rathbun, 1921) (Crustacea: Brachyura: Ocypodidae), a Fiddler Crab Endemic to Taiwan, with its Phylogenetic Position in the Family.

Xeruca formosensis is a species and genus of fiddler crab endemic to Taiwan, with limited distribution in western Taiwan and the offshore Penghu Islands. This study reports the complete mitochondrial genome (mitogenome) of this species using next-generation sequencing. The mitogenome contains 15,684 bp, comprising 13 protein-coding genes, 22 tRNAs, 2 ribosomal RNAs and a 750-bp intergenic space (control region). The nucleotide composition is biased toward A+T (69.4%). A phylogenetic analysis based on the concatenated protein-coding genes showed that the genera Xeruca Shih, 2015 and Tubuca Bott, 1973 are sister to each other. In addition, the phylogeny of the 16 available mitogenomes in the family Ocypodidae also supports the current systematics of this family based on one nuclear and two mitochondrial markers. As this species inhabits high intertidal mudflats with high temperature and high salinity, mitogenome analyses may help us understand the mechanisms of adaptation to extreme environments, as well as the connectivity of metapopulations based on mitogenomes from different populations.

First Record of the Genus Pseudohelice Sakai, Türkay & Yang, 2006 from India and Description of a New Pseudocryptic Species (Crustacea: Brachyura: Varunidae).

A new pseudocryptic species of the varunid crab genus Pseudohelice Sakai, Türkay & Yang, 2006, is described from India based on morphological and molecular evidence. The new species was collected from higher intertidal zones in the Vellar River estuary, Tamil Nadu, southeastern India, in a habitat composed of muddy and sandy sediment. Pseudohelice annamalai n. sp. is similar to P. subquadrata (Dana, 1851) and P. latreillii (H. Milne Edwards, 1837) in general form, but can be distinguished from the congeners by the characters of the infraorbital ridges, male first gonopod, and female vulvae. In addition, the mitochondrial cytochrome oxidase subunit I sequences also support the new species. The occurrence of Pseudohelice from India links the distribution gap between the western Indian Ocean and western Pacific Ocean. The new species provides additional evidence for the geographic isolation of the eastern Indian Ocean for some marine organisms.

Diversity and Distribution of Fiddler Crabs (Crustacea: Brachyura: Ocypodidae) around the Arabian Sea.

Nine species of fiddler crabs (Crustacea: Ocypodidae: Gelasiminae) are known from the Arabian Sea and adjacent waters (Red Sea, Gulf of Aden, Gulf of Oman and Arabian/Persian Gulf): five species of Austruca, one Cranuca, two Gelasimus and one Tubuca. COI sequence data match morphological species boundaries and shows high connectivity within each. The fauna is highly endemic, with three species of Austruca (A. albimana, A. iranica and A. sindensis) confined to this region, and four others restricted to the Indian Ocean. restricted to the Indian Ocean. Austruca albimana and A. iranica speciated locally and now have narrowly overlapping ranges in Oman. Our results confirm the westernmost distributions of Austruca annulipes and Tubuca alcocki are Pakistan and the Red Sea, respectively. A key for the nine species is also provided to help identification.

Systematics and Biogeography of Fiddler Crabs -A Special Issue in Zoological Studies.

Fiddler crabs are a fantastic group of intertidal brachyuran crabs, and the research fields focused on their biodiversity, phylogeography, phylogenomics, and larval biology are still in developing stages. In this special issue, seven articles are included focusing on the diversity, phylogeography, mitogenome phylogeny and larval morphology of fiddler crabs, covering the regions of the Indo-West Pacific and Americas. Results from this special issue open up further opportunities to study new species identification based on an integrative taxonomy approach, genomic-level phylogeny and larval morphology, especially in regards to the mitogenomes in the genera Cranuca, Gelasimus, Paraleptuca, and Uca for filling up the knowledge gap of fiddler crabs in the world.

Phylogeography of the Fiddler Crab Tubuca arcuata (Crustacea: Brachyura: Ocypodidae) in East Asia and Northern Vietnam.

The fiddler crab Tubuca arcuata (Crustacea: Ocypodidae: Gelasiminae) is widely distributed across East Asia and northern Vietnam. Particularly, this species inhabits estuarine mangroves and mudflats of the East Asian continent, as well as the main islands of Japan and the Ryukyus. By comparing sequences of the mitochondrial 16S, cytochrome oxidase subunit I (COI), and control region genes, two main clades of this species were elucidated. The northern (N) clade was mostly restricted to the region north of the Taiwan Strait, whereas the wide (W) clade could be found throughout the entire range inhabited by this species. Based on the distribution of the ancestral haplotypes of COI and the divergence time of the two clades, our findings suggest that the land bridge barrier present in the Taiwan Strait during glaciations might have played an important role in their cladogenesis, approximately 0.93 million years ago. Here, we propose that the distribution of the ancestral haplotype of the W clade in the Ryukyus and the main islands of Japan was determined by the Paleo-Kuroshio Current, whereas the modern distribution pattern is shaped by the modern Kuroshio Current and other warm currents during the crab reproduction season in the summer.

Diversity and Distribution of Fiddler Crabs (Crustacea: Brachyura: Ocypodidae) in Vietnam.

Based on recently collected material and records in the literature, 14 species of fiddler crabs (Crustacea: Ocypodidae: Gelasiminae) are reported from Vietnam. DNA barcoding analyses using the mitochondrial gene COI (cytochrome c oxidase subunit I) was performed to identify examined materials and their precise distributional range. Thirteen species-level taxa are identified and, with the exception of Galsimus borealis and G. vocans, have minimum interspcific divergences of at least 7.27%. The identified species include seven species of Tubuca Bott, 1973, three of Austruca Bott, 1973 and three of Gelasimus Latreille, 1817, and one Paraleptuca Bott, 1973. Two new records of Vietnam are herein reported: Tubuca rhizophorae and T. dussumieri. The southernmost distribution limits of East Asian G. borealis, T. acuta and T. arcuata are in northern Vietnam, A. lactea in central Vietnam, whereas northernmost limit of Southeast Asian T. rhizophorae and T. forcipata in southern Vietnam. A dichotomous key to identify the 14 Vietnamese species is provided.

First Zoeal Stage of 15 Species of Fiddler Crabs (Crustacea: Brachyura: Ocypodidae) from Taiwan.

Fiddler crabs (Brachyura: Ocypodidae: Gelasiminae) in Taiwan consist of 5 genera and 15 species, but knowledge of their larval development is limited to just 3 species, namely Austruca lactea, Tubuca arcuata, and Xeruca formosensis. In our study, the morphology of the first zoeal stage (zoea I) of the 15 species is described and compared to previous studies. The results show that the characters of zoea I can be used to distinguish the five studied genera and most species (except three groups, "Gelasimus borealis, G. jocelynae and G. vocans", "Paraleptuca crassipes and P. splendida" and "Tubuca arcuata, T. coarctata and T. paradussumieri"). The lateral spines on the carapace in zoea I are suggested to be a unique character in the Ocypodinae because they are absent in the Gelasiminae and Ucidinae, which supports the current systematics of the Ocypodidae.

Two new freshwater crab species of the genus Nanhaipotamon Bott, 1968 (Crustacea, Decapoda, Potamidae) from Huizhou, Guangdong Province, southern China.

Two morphologically distinct new species of Nanhaipotamon Bott, 1968, are described from Huizhou, Guangdong Province, southern China. The smooth carapace and lack of flagellum on the third maxilliped exopod immediately separate N. incendium n. sp. from all other known Nanhaipotamon. It is also the first species of this genus to be recorded from a relatively high altitude of 700 m a.s.l. Nanhaipotamon aureomarginatum n. sp. is externally much more typical of species of its genus but can be distinguished from congeners by its unique male first gonopod. The two new species are more or less sympatric with a morphological disparate congener, which we tentatively assign as N. aff. aculatum Dai, 1997 and N. aff. hongkongense (Shen, 1940), respectively, but with different habitats. A genetic analysis using the mitochondrial cytochrome oxidase subunit I shows that while the two new species are sufficiently distinct from other known species of Nanhaipotamon, they have extraordinarily close relationships with their respective sympatric congeners, which calls for further investigation. The ecology of these two new species are also noted.

Geothelphusa boreas, a new montane freshwater crab (Crustacea: Potamidae: Geothelphusa) from northeastern Taiwan, and the identity of G. hirsuta Tan amp; Liu, 1998.

A new freshwater crab is described from the montane area in northeastern Taiwan based on morphological and molecular evidence. Geothelphusa boreas sp. nov., from the Fushan Botanical Garden situated around New Taipei City and Yilan County, is distinct from similar congeners by the structure of the male first gonopod and the proportions of the male thoracic sternites. In addition, after comparing the holotypes of G. takuan and G. hirsuta Tan Liu, 1998, no substantial difference could be found. Molecular evidence from mitochondrial cytochrome oxidase subunit I also supports the recognition of the new species and the conspecificity of G. hirsuta with G. takuan.

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 & Duris, 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.

Morphological and Genetic Variation Among Populations of the Fiddler Crab Minuca burgersi (Holthuis, 1967) (Crustacea: Brachyura: Ocypodidae) from Shores of the Caribbean Basin and Western South Atlantic Ocean.

For this study, in addition to museum vouchers, 1437 specimens of Minuca burgersi (Holthuis, 1967) were collected from crab colonies at 105 locations in the western Atlantic Ocean to examine diversity in a species with a large geographic range. Both allometric and geometric morphometry were coupled with the molecular analysis of DNA to give a broader perspective of intraspecific variability in this species. A total of 1153 specimens from the Caribbean Sea and the Atlantic coast of South America demonstrated that M. burgersi from both regions are very similar in their pattern of growth. The average carapace width (CW) for Caribbean is larger than the average for South American males and females. However, size distribution based on CW is unimodal in Caribbean and bimodal in South American populations. The carapace length-width ratio is about 0.68 in females and 0.66 in males. South American males express asymmetric elongation of the cheliped in smaller CW intervals than Caribbean males. In a sample of 259 females, carapace shape is distinct between South American and Caribbean populations. Caribbean populations have less swelling in the branchial regions than South American populations. The swelling correlates primarily with geographic region and to a lesser degree with substrate and salinity. Molecular data from the 16S rDNA and cytochrome c oxidase subunit I (COI) reveal three clades within Minuca burgersi. Two clades are distributed in the Caribbean and the third in eastern South America. The timing of divergence between Caribbean and South American clades is coincident with an increased rate of water and sediment outflow from the Amazon as inferred from the geologic record. Current patterns and associated gene flow within the Caribbean were subsequently influenced by the closing of the Isthmus of Panama. We speculate that various populations may employ different larval dispersion mechanisms resulting in genetic heterogeneity. Consequently, there is considerable biological divergence among populations of M. burgersi in the Caribbean and South America.

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.

A New Genus and Two New Species of Freshwater Crab (Crustacea: Brachyura: Potamidae) with Unusual Coiled Tip of Male Second Gonopods from Yunnan, Southwestern China.

Two new species of a new genus, Tortomon puer n. gen. n. sp. and T. gejiu n. gen. n. sp. are described from southern Yunnan, southwestern China, based on the morphology and mitochondrial 16S rDNA sequences. The new genus resembles Tenuipotamon Dai, 1990 and Parvuspotamon Dai & Bo, 1994, but can be separated by characters of the male thoracic sternum, male pleon, male first gonopod, and especially the coiled tip of the male second gonopod. The latter character easily separates Tortomon n. gen. from known potamid genera. Notes on the general biology of the two new species are also included.

A New Fiddler Crab of Austruca Bott, 1973, Closely Related to A. perplexa (H. Milne Edwards, 1852) (Crustacea: Brachyura: Ocypodidae), from the South Pacific Islands.

A new species of fiddler crab, Austruca citrus n. sp. from Fiji, Wallis & Futuna, and Samoa, in the South Pacific is described based on morphological and molecular evidence. This species is closely related to Austruca perplexa (H. Milne Edwards, 1852), but can be distinguished by a suite of characters, including adult size, carapace morphology, shape and coloration of the major chela, the ratio of major pollex length as a function of carapace width, and male first gonopod form. The molecular evidence of the mitochondrial 16S rDNA and cytochrome oxidase subunit I (COI) supports these morphological differences.