Review of grapsoid families for the establishment of a new family for Leptograpsodes Montgomery, 1931, and a new genus of Gecarcinidae H. Milne Edwards, 1837 (Crustacea, Decapoda, Brachyura, Grapsoidea MacLeay, 1838)

New insights into the adaptation mechanism of Cardisoma armatum hepatopancreas in the terrestrial environment by transcriptome analysis

As a typical species of Gecarcinidae, Cardisoma armatum has adapted to the terrestrial environment. Meanwhile, C. armatum with unique living habits provides an excellent model for exploring the terrestrial adaptation mechanism of crabs. In this study, we have conducted a comprehensive transcriptomic analysis of C. armatum, aiming to deepen our understanding of the adaptive mechanisms operating within two groups: the air-exposed (AE) group and the water-immersed (WI) group, over eight hours. Genes that showed differential expression about adaptation to terrestrial environments were categorized into three groups: immune regulation, antioxidant system, and ion transport. The transcriptomic analysis also revealed a significant increase in the expression of genes related to immune response, antioxidant systems, and ion transport, such as the mitogen-activated protein kinase signaling pathway, tumor protein 53, superoxide dismutase 1, superoxide dismutase 2, solute carrier family 9 member A3, and Na+/K+/2Cl- cotransporter, indicating that C. armatum responds positively to changes in habitat. This study aims to furnish a molecular rationale for the adaptive mechanisms that terrestrial and semi-terrestrial crab species exhibit in their terrestrial habitats, thereby contributing to a deeper understanding of their evolutionary adaptations.

Ngan mayla gen. et sp. nov, a new blind potamid cave crab from Borneo, Kalimantan (Crustacea: Decapoda: Brachyura: Potamoidea, Potamidae), and three other unidentified cave crabs from the same region

We here report on freshwater cave crabs of the families Potamidae and Gecarcinucidae in East Kalimantan, Sarawak, Indonesia in Borneo. A new genus and species of potamid crab, Ngan mayla, is described from Lubang Gedung Cave in the Merabu Karst. With its bullet-shaped eyes, Ngan mayla gen. et sp. nov. is totally blind and also displays the characters associated with an obligate cave-dwelling life, namely that it is dolichopod and fully depigmented. The closest genus and species is Cerberusa caeca Holthuis, 1979, from northern Sarawak. Highly modified, Ngan mayla gen. et sp. nov. proves to be among the most troglobitic of the known subterranean potamids, of which there were currently only seven in the Old World, with only four simultaneously being completely blind, entirely depigmented and dolichopod (Cerberusa caeca Holthuis, 1979, Diyutamon cereum Huang, Shih & Ng, 2017 and Phasmon typhlops Huang, Ahyong & Shih, 2020, to which must be added today Ngan mayla gen. et sp. nov.). Ngan mayla gen. et sp. nov. is easily distinguished from other potamid genera by its chelipeds bearing numerous acute teeth, spines (some horn-tipped) and short simple setae or spine-like setae on all articles. Two young female crabs collected in 2010 at the same area (Merabu Karst) but from a different cave, the Lubang Tebot Cave, could not be identified to specific level: an Isolapotamon sp., and a gecarcinucid with very long legs, pale colouration and slightly modified but black-pigmented eyes, close to Balssiathelphusa Bott, 1969, could possibly belong to a new genus. Some information on New World troglobitic crabs is provided.

Two new species and a new record of infaunal crabs (Decapoda: Brachyura: Pinnotheridae and Varunidae) from Oman and Saudi Arabia

Recent surveys of shallow subtidal soft-bottom habitats of Oman and the Red Sea coast of Saudi Arabia have uncovered several crabs new to science. Stemming from these efforts, two crab species are herein described as new to science. The first is a new pinnotherid crab, Indopinnixa arabica n. sp., from northern Oman. The other is a new species of varunid crab, Gopkittisak ngankeeae n. sp., from northern, eastern and southern Oman. Additionally, the first known males of another varunid crab, Brankocleistostoma fossulum (Barnard, 1955), are described and illustrated based on material from eastern Oman and southern Saudi Arabia, also representing a new record of the species for the Arabian region.

Molecular Phylogeny and Evolution of the Tuerkayana (Decapoda: Brachyura: Gecarcinidae) Genus Based on Whole Mitochondrial Genome Sequences

Tuerkayana is of particular interest because it has been separated, in recent years, from Cardisoma and Discoplax but studies of its taxonomic status, especially from a whole mitochondrial genome perspective, have been lacking. In this study, the mitogenomes of four species (Tuerkayana magnum, Tuerkayana rotundum, Tuerkayana hirtipes, and Tuerkayana celeste) of Tuerkayana are sequenced and contrasted with other species in Brachyura for the first time. The phylogenetic tree of Brachyura, which includes 206 crab species (189 species of Brachyuran and 17 Anomura species) with a complete mitogenome, was constructed to evaluate the phylogenetic position of Tuerkayana and Gecarcinidae within Brachyuran, and explore the monophyly of Gecarcinidae. Furthermore, two single gene trees based on cox1 and 16SrRNA separately within interspecies of Gecarcinidae were reconstructed, providing molecular evidence for Tuerkayana and further clarifying the division of genera in Gecarcinidae. Based on the mitogenome dataset of 206 crabs, the branch-site model was utilized to explore selective pressure in individual codons with CodeML. The strong selective pressure shown in nad6 indicates that it may have played a significant role in the evolution of Gecarcinidae.

Sexual Maturity of an Endemic Insular Land Crab: Priority Information toward the Conservation of Johngarthia lagostoma

AbstractInsular land crabs (Gecarcinidae) can transit between terrestrial and aquatic environments and inhabit vacant ecological niches that other species do not occupy in oceanic islands. During the reproductive period, these crabs migrate between residential and reproductive areas; this is a critical moment because individuals are more vulnerable to stressful conditions, especially species occupying anthropized islands. Currently, many insular crab species are considered threatened; yet few studies have evaluated the biology of this group, especially the size at which individuals reach sexual maturity. Here, we evaluate the size at the onset of morphological, physiological, and functional maturity for the insular land crab Johngarthia lagostoma in Trindade Island (Brazil) and assess the chronology of the events underlying those processes. Males and females exhibited the same order of occurrence of the different maturity processes, starting by being morphologically, physiologically, and, finally, functionally mature at similar sizes (about 56 mm carapace width). This value corresponds to at least half of the maximum size that J. lagostoma reaches in Trindade Island and is close to the average relative value registered to other Gecarcinidae species. Considering the current decline in the population of insular crabs, such estimates can be used in management programs, mainly for the definition and protection of breeding and recruitment areas. Specifically, our results can be used toward the conservation of J. lagostoma, which is currently classified as endangered in Brazil, especially in the isolated population of Trindade Island.

Molecular phylogeny of Thoracotremata crabs (Decapoda, Brachyura): toward adopting monophyletic superfamilies, invasion history into terrestrial habitats and multiple origins of symbiosis

The Thoracotremata is a large and successful group of "true" crabs (Decapoda, Brachyura, Eubrachyura) with a great diversity of lifestyles and well-known intertidal representatives. The group represents the largest brachyuran radiation into terrestrial and semi-terrestrial environments and comprises multiple lineages of obligate symbiotic species. In consequence, they exhibit very diverse physiological and morphological adaptations. Our understanding of their evolution is, however, largely obscured by their confused classification. Here, we resolve interfamilial relationships of Thoracotremata, using 10 molecular markers and exemplars from all nominal families in order to reconstruct the pathways of lifestyle transition and to propose a new taxonomy corresponding to phylogenetic relationships. The results confirm the polyphyly of three superfamilies as currently defined (Grapsoidea, Ocypodoidea and Pinnotheroidea). At the family level, Dotillidae, Macrophthalmidae, and Varunidae are not monophyletic. Ancestral state reconstruction analyses and divergent time estimations indicate that the common ancestor of thoracotremes already thrived in intertidal environments in the Late Cretaceous and terrestrialization became a major driver of thoracotreme diversification. Multiple semi-terrestrial and terrestrial lineages originated and radiated in the Early Eocene, coinciding with the global warming event at the Paleocene-Eocene Thermal Maximum (PETM). Secondary invasions into subtidal regions and colonizations of freshwater habitats occurred independently through multiple semi-terrestrial and terrestrial lineages. Obligate symbiosis between thoracotremes and other marine macro-invertebrates evolved at least twice. On the basis of the current molecular phylogenetic hypothesis, it will be necessary in the future to revise and recognize seven monophyletic superfamilies and revisit the morphological character states which define them.

Sound production mechanism in the semiterrestrial crab Neohelice granulata (Brachyura, Varunidae)

Very few studies of sound production in the Brachyura have simultaneously identified the type of individuals (e.g., sex) producing acoustic signals, the structures involved in making sound and the social context. The emission and type of sound signals in Neohelice granulata were previously characterized, but the sex and the body structures involved in the sound production mechanism were not determined. In the present study, experiments conducted in the laboratory demonstrated that acoustic signals were produced by males through an up-down movement of the cheliped by rubbing the merus against the pterygostomial area of the carapace. The micromorphology of the merus showed that it has a ridge of tubercles which may act as a plectrum, while the pterygostomial area bears tubercles and might function as the pars stridens. Acoustic signals were displayed more frequently in the presence of receptive females. Agonistic encounters among males also occurred more often in the presence of receptive females. The authors propose that Neohelice granulata males use their chelipeds to produce sound signals in a mating context, probably to attract the receptive female and/or to repel other males when a receptive female is present. Thus, the display might have a reproductive function influencing mate choice.