Brachyuran Crabs Research Articles

Two New Species of Spheroid Ectoparasitic Isopods (Epicaridea: Dajidae) Attached to the Antennules of Brachyuran Crab Hosts, with Description of a New Genus and Species of Hyperparasite (Epicaridea: Cryptoniscoidea)

Two New Species of Spheroid Ectoparasitic Isopods (Epicaridea: Dajidae) Attached to the Antennules of Brachyuran Crab Hosts, with Description of a New Genus and Species of Hyperparasite (Epicaridea: Cryptoniscoidea)

Brachyuran crabs (Crustacea, Decapoda) from the remote oceanic Archipelago Trindade and Martin Vaz, South Atlantic Ocean.

Forty species of shore and shallow water brachyuran crabs are reported from the remote oceanic Archipelago Trindade and Martin Vaz (TMV), 11 of which were previously known from Trindade Island, 28 are recorded from the Archipelago for the first time, and one is a new species, Epialtus parvulus sp. nov. This brings the total known shore and shallow water decapod fauna of TMV to 99 species. The opportunity is taken here to elaborate on the taxonomy of the species reported from TMV. One new genus, Mecataleptodius, is recognized for two species, Cancer parvulus Fabricius, 1793, its type species, and Cataleptodius olsoni Manning Chace, 1990, endemic to Ascension Island. The following seven nominal species are synonymized: Acanthonyx dissimulatus Coelho in Coelho Torres, 1993; A. scutiformis (Dana, 1851a); Dromia gouveai Melo Campos Junior, 1999; Epialtus portoricensis Rathbun, 1923; Ranilia guinotae Melo Campos Junior, 1994; R. saldanhai H. Rodrigues da Costa, 1970; and Omalacantha garthi (Lemos de Castro, 1953). TMV is a subset of the western Atlantic crab fauna (23 species or 57.5%), also including 8 (20%) amphi-Atlantic species, 3 (7.5%) amphi-American, 3 (7.5%) endemic, 2 (5%) cosmopolitan, 1 (2.5%) known from both sides of the Atlantic and the Indo-West Pacific. The crab fauna of TMV, Ascension (AS) and Saint Helena (SH) are compared with one another as well as with that of the oceanic islands Fernando de Noronha (FN) and the Rocas Atoll (RA) by means of nonmetric multidimensional scaling (NMDS) applied to a dissimilarity matrix generated by Jaccards coefficient. TMV-FN-RA and AS-SH clustered into two distinct groups according to the composition of their crab fauna. The NMDS analysis ranked the species that cause segregation of the crab faunal assemblages among TMV, AS, and SH, while revealing a gradient in species composition between the two groups of islands (TMV-FN-RA and AS-SH) formed by the amphi-Atlantic species. Island isolation, age and size alone do not explain the existing differences in species richness among TMV, AS and SH. The taxonomic composition of the shallow water fauna in these islands is likely to have been determined by several variables that were interwoven differently along their evolutionary history.

A new genus and species of brachyuran crab (Crustacea, Decapoda) from the Aptian-Albian (Cretaceous) of the Araripe Sedimentary Basin, Brazil

A new brachyuran crab genus and species, Chronocancer camilosantanai, is described from carbonatic concretions of the Romualdo Formation of the Santana Group, Araripe Sedimentary Basin, northeastern Brazil. Chronocancer camilosantanai n. gen. n. sp. is provisionally assigned to the Orithopsidae. The new genus is superficially suggestive of the orithopsid Bellcarcinus Luque, 2014 (Upper Aptian of Colombia), of which it differs by a combination of characters including: carapace longer than wide, longitudinally suboval, wider anteriorly; internal supraorbital tooth broad triangular; anterolateral margins toothless; carapace hepatic, gastric and cardiac regions devoid of tubercles. The new species is briefly compared to all other known brachyurans found in the Araripe Sedimentary Basin.

Cretaceous Crustacea from plattenkalk deposits of Mexico

The Crustacea preserved in Cretaceous plattenkalk deposits from Mexico is revisited. New findings include isopods, palinurid lobsters, and crabs. Based on new material available, descriptions of previously reported species are extended. High diversity and abundance of Peracarida from the upper Aptian Sierra Madre El Espinal quarries (Chiapas) are synthesized, along with detailed images of a previously described palinurid species. The famous laminar red limestone quarries of the upper Albian Tlayúa Formation, Tepexi de Rodríguez (Puebla), yielded a new lobster and a pagurid, and nearly 100 complimentary crab specimens of Tepexicarcinus Feldmann, Vega, Applegate and Bishop, 1998, offer more information on its morphology and ontogeny. Arthropoda from the upper Albian El Doctor Formation, Muhi quarries (Hidalgo), include three new incomplete lobsters, an additional specimen of the penaeid Aeger hidalguensis Feldmann et al.2007 (whose morphology is compared with the A. tipularis () from the Upper Jurassic of Germany), and new specimens of an enigmatic Thylacocephala. From the Cenomanian Siera Madre Formation, El Chango quarries Chiapas, we illustrate shrimp, a poorly preserved phyllosoma larva, and a new brachyuran crab. The diverse and abundant crustaceans from the Turonian–Cenomanian El Rosario quarry (Múzquiz, Coahuila) are revisited, with preliminary interpretations of previously reported raninoids.

Brachyuran crab diversity and the population biology of Panopeus americanus on a tropical Sabellariidae (Polychaeta: Annelida) reef

This paper describes the species composition, abundance, and diversity of brachyuran crabs and the population structure of Panopeus americanus on a Sabellaria wilsoni reef on Caixa D’Água beach, a macrotidal sandy beach on the Amazon coast. Samples were collected monthly throughout a single natural growth–destruction cycle of the reef. Ten crab species were recorded, of which the most abundant were Panopeus americanus (83% of the individuals collected), Panopeus occidentalis (6.8%), and Menippe nodifrons (5.3%). The highest crab species richness was recorded during the eroded reef phase, reflecting the increase in habitat complexity, whereas the highest crab density was recorded during the reef recuperation period, reflecting an intense recruitment process. Juveniles and adults (including ovigerous females) of P. americanus and P. occidentalis were found at certain times on the reef, while for M. nodifrons, the largest species, most of the captured individuals were juveniles, and no ovigerous females were captured. These findings reflect the importance of the biogenic substrate provided by the S. wilsoni reef to the population biology of the crabs on the Amazon coast, with some species using the reef more permanently, including as breeding and nursery grounds. The results also showed that the structural cycle of bioconstructions determines changes in the crab assemblages.

Morphological characteristics and abundance of prokaryotes associated with gills in mangrove brachyuran crabs living along a tidal gradient.

Due to the chemico-physical differences between air and water, the transition from aquatic life to the land poses several challenges for animal evolution, necessitating morphological, physiological and behavioural adaptations. Microbial symbiosis is known to have played an important role in eukaryote evolution, favouring host adaptation under changing environmental conditions. We selected mangrove brachyuran crabs as a model group to investigate the prokaryotes associated with the gill of crabs dwelling at different tidal levels (subtidal, intertidal and supratidal). In these animals, the gill undergoes a high selective pressure, finely regulating multiple physiological functions during both animal submersion under and emersion from the periodical tidal events. We hypothesize that similarly to other marine animals, the gills of tidal crabs are consistently colonized by prokaryotes that may quantitatively change along the environmental gradient driven by the tides. Using electron microscopy techniques, we found a thick layer of prokaryotes over the gill surfaces of all of 12 crab species from the mangrove forests of Saudi Arabia, Kenya and South Africa. We consistently observed two distinct morphotypes (rod- and spherical-shaped), positioned horizontally and/or perpendicularly to the gill surface. The presence of replicating cells indicated that the prokaryote layer is actively growing on the gill surface. Quantitative analysis of scanning electron microscopy images and the quantification of the bacterial 16S rRNA gene by qPCR revealed a higher specific abundance of prokaryote cells per gill surface area in the subtidal species than those living in the supratidal zone. Our results revealed a correlation between prokaryote colonization of the gill surfaces and the host lifestyle. This finding indicates a possible role of prokaryote partnership within the crab gills, with potential effects on animal adaptation to different levels of the intertidal gradient present in the mangrove ecosystem.

The complete mitochondrial genome of the Atlantic ghost crabOcypode quadrata(Fabricius, 1787) (Brachyura: Ocypodidae: Ocypodinae)

AbstractThe semi-terrestrial Atlantic ghost crab Ocypode quadrata (Fabricius, 1787) is a medium-sized species that inhabits the supralittoral zone in sandy temperate and tropical beaches of the western Atlantic Ocean. Despite the relevant ecological role of O. quadrata and its use as a bio-indicator, there are currently few genetic and genomic resources for this species. This study assembled and characterized in detail the complete mitochondrial genome of O. quadrata from Illumina short paired-end reads. The software NOVOplasty assembled and circularized the complete mitochondrial genome of the Atlantic ghost crab with an average coverage of 162×, per nucleotide. The AT-rich mitochondrial genome of O. quadrata is 15,547 bp in length, consisting of 13 protein coding genes (PCGs), 22 transfer RNA (tRNA) genes, and two ribosomal RNA genes (rrnL and rrnS). A single 685 bp long non-coding nucleotide region is assumed to be the D-loop/control region. The observed gene order in O. quadrata is identical to that reported for all congeneric species with known mitochondrial genomes. A selective pressure analysis indicates that all the PCGs are under purifying selection. Differences in KA/KS ratios among genes indicate strong purifying selection in the cox1, cox2, cox3, and atp6 genes, and weaker purifying selection in the atp8 gene. The 22 tRNA genes range from 64 to 70 bp in length, and all the tRNAs show a conventional “cloverleaf” secondary structure except for trnS1 that is missing the D-arm, in agreement to that reported for other brachyuran crabs with tRNA secondary depictions published. A maximum likelihood phylogenetic analysis based on all PCGs that included a total of 18 species of crabs fully supported the monophyly of the family Ocypodidae. The monophyly of the subfamilies Ocypodinae and Ucinidae was also highly supported by the analysis. These results suggest that mitochondrial PCGs have “phylogenetic signal” to reveal natural relationships at high taxonomic levels in crabs belonging to the family Ocypodidae. This study represents a new genomic resource for this ecologically relevant bioindicator ghost crab.

On the collection of marine crabs (Decapoda: Brachyura) in the Zoological Survey of India, Western Regional Centre, Pune, with a note on the taxonomy of Sphaerozius scaber (Fabricius, 1798) (Menippidae).

The Zoological Survey of India, Western Regional Centre, Pune (ZSI-WRC) contains 1887 specimens of mostly unstudied marine brachyuran crabs. The present systematic study on the marine crabs of ZSI-WRC reports 62 species in 44 genera, 18 families and nine superfamilies. Of these, four genera and 13 species are new distributional records within India. We also record three species for the first time from the Indian waters: Metopograpsus cannicci Innocenti, Schubart Fratini, 2020 (Grapsidae MacLeay, 1838), Varuna yui Hwang Takeda, 1986 (Varunidae H. Milne Edwards, 1853), and Ilyograpsus paludicola (Rathbun, 1909) (Macrophthalmidae Dana, 1851). The record of Varuna yui is significant as it is the first time it has been found from the western Indian Ocean. The subfamily Ilyograpsinae tevi, 2005, has likewise not previously been reported from India. The taxonomy of the poorly known menippid crab, Sphaerozius scaber (Fabricius, 1798), is clarified with the designation of a lectotype, and its taxonomy is discussed. Sphaerozius scaber can be distinguished from the only congener S. nitidus Stimpson, 1858, by its prominently tuberculated carapace, palm and carpus of the chelipeds, and the strongly curved male first gonopod, with the distal part gently tapering into a truncate tip. Sphaerozius scaber is a new addition to the west coast of India. With the inclusion of the present new records, India is now known to have 939 species of marine brachyuran crabs in 375 genera of 63 families.

First reports of protists in land crabs of the family Gecarcinidae (Crustacea: Decapoda: Brachyura) suggest a relatively widespread phenomenon

ABSTRACT Eccrinales are protists of the class Mesomycetozoea exclusively found in the digestive tract of marine, freshwater and terrestrial arthropods. Isopods are the only terrestrial crustaceans from which eccrinids have been reported. Among brachyuran crabs, eccrinids were exclusively reported in grapsid and ocypodid crabs, with a percentage of occurrence ranging from 5% to 100% in the respective species. The eccrinid Enteromyces callianassae Lichtwardt, 1961 has been found in the guts of various decapod crustacean species in marine habitats and intertidal mud or sand flats in Chile, France, Japan and the USA. Semi-terrestrial species of Leptuca and Minuca were the most terrestrial crabs in which E. callianassae has been observed. Here we report the presence of E. callianassae in stomachs of the land crab Gecarcinus lateralis. These are the first observations of protists in gecarcinid crabs, which are regarded as the most terrestrial brachyuran crabs. The presence of E. callianassae in 11% of 74 examined stomachs from males and females of G. lateralis from three locations in Costa Rica suggests that the occurence of E. callianassae in these crabs is a relatively widespread phenomenon. Considering that these highly terrestrial crabs are important herbivores on island and continental landscapes, the presence of eccrinids in the stomachs of these crabs may have important implications for the carbon cycling in coastal ecosystems.

Molecular phylogeography reveals multiple Pleistocene divergence events in estuarine crabs from the tropical West Pacific.

Due to the lack of visible barriers to gene flow, it was a long-standing assumption that marine coastal species are widely distributed, until molecular studies revealed geographically structured intraspecific genetic differentiation in many taxa. Historical events of sea level changes during glacial periods are known to have triggered sequential disjunctions and genetic divergences among populations, especially of coastal organisms. The Parasesarma bidens species complex so far includes three named plus potentially cryptic species of estuarine brachyuran crabs, distributed along East to Southeast Asia. The aim of the present study is to address phylogeography and uncover real and hidden biological diversity within this complex, by revealing the underlying genetic structure of populations and species throughout their distribution ranges from Japan to West Papua, with a comparison of mitochondrial COX1 and 16S rRNA gene sequences. Our results reveal that the P. bidens species complex consists of at least five distinct clades, resulting from four main cladogenesis events during the mid to late Pleistocene. Among those clades, P. cricotum and P. sanguimanus are recovered as monophyletic taxa. Geographically restricted endemic clades are encountered in southeastern Indonesia, Japan and China respectively, whereas the Philippines and Taiwan share two clades. As individuals of the Japanese clade can also be found in Taiwan, we provide evidence of a third lineage and the occurrence of a potential cryptic species on this island. Ocean level retreats during Pleistocene ice ages and present oceanic currents appear to be the main triggers for the divergences of the five clades that are here addressed as the P. bidens complex. Secondary range expansions converted Taiwan into the point of maximal overlap, sharing populations with Japan and the Philippines, but not with mainland China.

Brachyuran crabs (Crustacea: Decapoda) in the limestone caves of Thailand, with a checklist of freshwater cave-dwelling crabs in Southeast Asia

Brachyuran crabs (Crustacea: Decapoda) in the limestone caves of Thailand, with a checklist of freshwater cave-dwelling crabs in Southeast Asia

Trophic niches of two predator fish cohabiting in the Algerian coastal ecosystem: Scorpaena porcus (Linnaeus, 1758) and Scorpaena notata (Rafinesque, 1810)

The diet of adult specimens of black scorpionfish Scorpaena porcus (Linnaeus, 1758) and small red scorpionfish Scorpaena notata (Rafinesque, 1810), collected from the Algerian coast was studied using different coefficients and trophic indexes. The inventory of ingested prey indicates that the focal species have a diverse diet that covers different zoological groups. Their feeding spectrum is mainly composed of brachyuran crabs and other crustaceans such as isopods and shrimp. Fish and molluscs are only occasionally ingested. The vacuity coefficient average exceeded the estimated rate of 40%. The observed monthly fluctuations revealed a seasonal alimentary rhythm. The foraging activity of the two scorpionfish decreases in summer, during gonad maturation. This decrease is highlighted by the increase in the vacuity coefficient and the decrease in the repletion index. Despite a similarity in the food bolus, the two co-occurring fish exhibit a specialized diet. This was observed especially in mature individuals. In conclusion, our results demonstrated a very strong overlap of niches between two scorpionfish species.

Burrow Morphology of Brachyuran Crab Dotilla blanfordi Alcock, 1900 from Gulf of Khambhat, Gujarat, India

The present study was conducted to understand the burrow morphology of brachyuran crab Dotilla blanfordi Alcock, 1900 at Dandi beach located in Gulf of Khambhat of Gujarat state, India. Burrows were selected randomly and their opening diameter was recorded. Diluted resin was poured in the burrows to generate burrow cast. If the occupant crab emerges out of the burrow, it was captured and carapace width and gender was recorded. The shapes of complete burrow casts were identified and measurements of various morphological characters of burrow cast were recorded. Total 7 different burrow shapes were identified, out of which single tube burrow was the most common as compared to other burrow shapes. The crab carapace width showed significant relationship with burrow opening diameter, burrow depth, burrow length and burrow volume. Juveniles (3.45 mm CW) were making burrow of all the seven shapes. Burrow depth, length and volume were significantly higher in adult crabs as compared to juveniles. No significant variation was observed between burrows of male and female individuals. The present study showed that burrow morphology is highly affected by the crab body size and also varies significantly with different life stages of the crab. Juveniles make shallow and simple burrows as their smaller gill areas stores lesser amount of respiratory water which needs to be changed frequently. However, adults make complex burrows to perform various tasks including copulation and reproduction.

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.

Functional responses of mangrove fauna to forest degradation

Structural degradation of mangroves through the partial removal of trees is globally pervasive and likely to affect ecological functioning, including habitat provisioning for biodiversity. Biodiversity responses will depend on the severity of degradation, yet few studies have contraste and quantified several degradation states. Addressing this knowledge gap, we sampled faunal diversity across a range of mangrove forests in southern Kenya. Canopy cover was the strongest predictor of faunal responses among forest structural variables. Faunal abundance, species richness and biodiversity all decreased with reduction in canopy cover, and taxonomic and functional composition changed. The trophic diversity of crabs peaked at intermediate canopy cover, with degraded habitats having more generalist species and fewer specialists. Functional redundancy was unaffected by canopy thinning. The decline in functional diversity and richness of brachyuran crabs with canopy cover implies that resource-use efficiency weakens with increasing degradation. Our results are indicative of significant alterations to forest functioning with degradation, because epibenthic fauna are important regulators of mangrove ecosystem processes, including nutrient cycling and carbon.

Pleolobites (Decapoda: Brachyura) from the Paleogene of Africa revisited, with implications on taxonomy of fossil portunoid crabs

Since its first description in 1960, the brachyuran crab genus Pleolobites was restricted to the Eocene (Ypresian) strata of Ivory Coast. Here, we report newly collected specimens that indicate its presence in the Paleocene (Thanetian) of Togo. This monotypic genus has been classified within various higher taxa, including Portunidae, Macropipidae, and Carcinidae, depending on the concurrent classification of portunoid crabs. Through the re-examination of the type material of Pleolobites erinaceus, the most recent assignment of Pleolobites within the subfamily Polybiinae of the family Carcinidae is disputed herein. Nevertheless, we refrain from assigning Pleolobites to any family and opine for its placement as Portunoidea incertae sedis. Additionally, the crab genus Rhachiosoma, morphologically similar to Pleolobites, is also removed from Polybiinae and placed in Portunoidea incertae sedis. It is further argued that Palaeoxanthopsis, Paraverrucoides, Parazanthopsis, and Verrucoides currently classified within the family Palaeoxanthopsidae of the superfamily Carpilioidea show striking similarities with Pleolobites and Rhachiosoma, including the morphology of dorsal carapace, thoracic sternum and pleon. Additionally, chelipeds with a spiny propodal margin and multi-lobed serial finger-teeth, otherwise characteristic for Portunoidea are found in Parazanthopsis and Palaeoxanthopsis. It remains to be investigated whether these resemblances are the result of evolutionary convergence or close phylogenetic relationships. add a blank line

The Identity of Homoioplax haswelli (Miers, 1884) (Crustacea: Decapoda: Brachyura).

The brachyuran crab Pseudorhombila haswelli Miers, 1884, described on the basis of two juveniles from the Arafura Sea, is a poorly known species of uncertain systematic position. It was made the type and only species of Homoioplax Rathbun, 1914, and assigned to the Prionoplacinae (Goneplacidae). Subsequent revisions of the goneplacids showed Prionoplacinae to be a junior synonym of Eucratopsinae Stimpson, 1871, as a member of the Panopeidae Ortmann, 1893, but no one has re-evaluated the position of Homoioplax. As a result, Homoioplax has remained in the Panopeidae as the only Indo-West Pacific representative of the family. This study assesses the systematic status of Homoioplax haswelli based on a re-examination of the type and other material of the species. Homoioplax haswelli is here attributed to Carcinoplax H. Milne Edwards, 1852 (Goneplacidae), justifying the recognition of the species described by Miers as C. haswelli. Moreover, Carcinoplax haswelli is shown to be a senior synonym of C. sinica Chen, 1984, described from the South China Sea. Therefore, C. haswelli is now known to range from southern Taiwan and the Philippines, through the South China Sea, northern Vietnam, the eastern waters of Singapore to the Madura Straits in eastern Java and Arafura Sea, northern Australia, at 25-187 m, but usually less than 100 m depth.

Transcriptional Landscape of Small Non-coding RNAs in Somatic and Gonadal Tissues of Brachyuran Crabs (Genus Eriocheir and Portunus)

Small non-coding RNAs (sncRNAs) play important roles in transcriptional and post-translational gene silencing in animals. However, the sncRNAs were not well studied in Brachyuran crabs, especially for the PIWI-interacting RNAs (piRNAs), which suppress transposon activity to maintain the germ lines genomic integrity. To unravel the sncRNAs expression profiling and genomic function in Brachyuran crabs, we generated a comprehensive small RNA dataset by small RNA sequencing (sRNA-seq) of three crabs. Abundant known and novel miRNAs were identified and characterized in these crabs. Among these miRNAs, 12 miRNAs were detected in all crabs, and another 41 miRNAs were detected in both of E. sinensis and E. japonica. In addition, abundant piRNA reads with a significant ping-pong signal were discovered in the ovaries and testis of Brachyuran crabs, which might associate with transposon silencing in germ lines. Our dataset would serve as important reference data for future genomic and genetic studies on small RNAs in these crabs and related species.

Decapod crustaceans from the lower Miocene Qom Formation of the Isfahan area, Central Iran

From the lower Miocene (Burdigalian) of the Qom Formation, exposed in three sections (Kuh-e-Donbeh, Bagher-Abad, and Vartun) in Central Iran, a deca-pod crustacean assemblage is described. The specimens exhibit two modes of preservation: carapaces (either isolated or with attached appendages) and isolated cheliped elements. All studied specimens are fractured and/or eroded. Based on this moderately preserved material, three brachyuran crab taxa are identified, including Mursia cf. lienharti (Bachmayer, 1962), Palaeocarpilius rugifer Stoliczka, 1871, and Necronectes sp. The occurrence of P. rugifer represents the youngest confirmed occurrence of the species, whereas other two taxa represent the first confirmed Iranian occurrences of respec-tive genera. This report enriches our knowledge on Miocene decapod assemblages of Iran, and thus helping to better understand the decapod migratory patterns along the Tethyan Sea-way.

Review of range extensions of tropical brachyuran crabs into temperate waters of southern Africa

Abstract We compiled known occurrence records of seven species of crabs identified in the literature and one documented in this report as having undergone range extensions in southern Africa. Of these eight species, six (Austruca occidentalis, Neosarmatium africanum, Ocypode ceratophthalmus, Portunus segnis, Tubuca urvillei, and Varuna litterata) have extended their ranges either across a major biogeographic boundary that separates the subtropical and warm temperate ecoregions of this coast, or into estuaries that historically lack mangrove forests. For the seventh and eighth species, Charybdis smithii and Scylla serrata, we were unable to find any distributional data that supported poleward range extension. In addition, we contribute the first record of the blue swimming crab, P. segnis, from the temperate south coast of South Africa. This early detection is likely to be part of an ongoing regional trend of tropical-adapted brachyuran crab species extending their ranges into temperate ecoregions.