Marine species formation along the rise of Central America: The anomuran crab Megalobrachium.

The evolution of marine neotropical shallow water species is expected to have been greatly affected by physical events related to the emergence of the Central American Isthmus. The anomuran crab Megalobrachium, a strictly neotropical porcellanid genus, consists of four species in the West Atlantic (WA) and nine in the East Pacific (EP). Dispersal is limited to a relatively short planktonic phase, which lasts approximately two weeks. We obtained DNA sequences of three mitochondrial and two nuclear genes of all but one species of Megalobrachium to construct a time-calibrated phylogeny of the genus and its historical phylogeography, based on the reconstruction of ancestral areas. The topology of the phylogenetic trees of Megalobrachium produced by Bayesian Inference (BI) and Maximum Likelihood (ML) were virtually congruent. The genus is monophyletic with respect to other porcellanids. Ancestral area reconstruction indicates that it arose in the eastern Pacific 18 million years ago and diversified into at least 13 species that are currently formally recognized and three additional species indicated by our data. Most morphological variation appears to have followed phylogenetic differentiation, though some cryptic speciation has also occurred. Four geminate clades in this genus implicate the gradual emergence of the Central American Isthmus in this diversification, but events preceding the final separation of the oceans as well as within-ocean events after the cessation of water connections were also important.

Description of a new species of the Petrolisthesgalathinus complex from the Caribbean Sea, and resurrection of Petrolisthesoccidentalis from the East Pacific (Crustacea, Anomura, Porcellanidae).

The Petrolisthesgalathinus complex currently consists of six American species distributed in the West Atlantic, including the amphi-American P.galathinus. All species in the complex are similar in their adult morphology but differ in colour, size, larval morphology, and shape of the adult sternal plate. The West Atlantic species have different geographic ranges, which overlap in the southern Caribbean. Previously published molecular data support the monophyly of the complex, and the reciprocal monophyly of each described species and further clades corresponding to different colour morphs. Here, the morph P.caribensis "Blue" is described as Petrolisthescoeruleussp. nov., and Petrolisthesoccidentalis is formally resurrected for the Pacific individuals of P.galathinus. By adding these two species to the P.galathinus complex, this now consists of eight species. Colour illustrations of all species and colour morphs are provided and their geographic distributions and ecological ranges are discussed and updated.

A new species of Petrolisthes (Crustacea, Anomura, Porcellanidae) inhabiting vermetid formations (Mollusca, Gastropoda, Vermetidae) in the southern Caribbean Sea.

Petrolisthes virgilius sp. nov. from the Caribbean Sea of Colombia is described. The new species resembles P. tonsorius morphologically but differs from it principally by its color and habitat. Petrolisthes tonsorius is brown or blueish brown and occurs under intertidal boulders strongly exposed to water movement. Petrolisthes virgilius sp. nov. is pale brown to beige and lives exclusively in intertidal areas dominated by vermetid snails, exposed to heavy wave action. The entangled tubular shells of vermetids are cemented to each other and to a hard substrate like beach rock, forming a microhabitat for the new crab species and other porcellanids of the genera Neopisosoma and Clastotoechus. Large genetic distances between DNA sequences of the mitochondrial 16S rDNA gene from P. virgilius sp. nov. and P. tonsorius confirmed that they comprise different species. Petrolisthes virgilius sp. nov. is the 53rd member of the West Atlantic porcellanid fauna.

A new species of Polyonyx (Crustacea, Anomura, Porcellanidae) inhabiting polychaete-worm tubes (Annelida, Chaetopteridae) in the Indo-West Pacific.

Polyonyxsocialis sp. n. from the South China Sea of Vietnam is described. The new species was collected in a previous study that compared the vertebrate and invertebrate symbiont communities living in the tubes of two syntopic species of the polychaete genus Chaetopterus. Polyonyxsocialis sp. n. inhabits the tubes of the smaller polychaete species as a heterosexual pair, and frequently shares the cavity of the host's tube with a larger porcellanid, P.heok, also present as a male-female pair, and with a species of trinchesiid nudibranch. Less frequently, the new species shares its host with a heterosexual pair of a larger species of pinnotherid crab. Polyonyxsocialis sp. n. belongs to the P.sinensis group, a world-wide distributed morphological line within the heterogeneous genus Polyonyx. Most species in this group are obligate commensals of chaetopterid polychaetes. The crabs have a transversally cylindrical habitus, which enables them to move laterally along the worm tubes with ease. Polyonyxsocialis sp. n. is a relatively small species that lives attached to the inner walls of the polychaete tube. The small size and flattened chelipeds and walking legs of the new species confers it an advantage to cohabiting the same worm tube with larger decapod species occupying most of the tube's cavity.

On a new commensal species of Aliaporcellana from the western Pacific (Crustacea, Decapoda, Porcellanidae).

Aliaporcellanaspongicolasp. n. from the Philippines and Indonesia is described. The new species has been frequently photographed by divers because of its striking coloration, but has not been described yet. Aliaporcellanaspongicolasp. n. is in fact a widespread commensal of barrel sponges of the genus Xestospongia and other sponges. Morphological characters and ecological information of all described species of Aliaporcellana, and of other porcellanids associated with sponges and soft corals, suggest that all members of the genus are commensals, and that similar morphological adaptations to dwelling on these hosts have evolved independently in different evolutionary lines within Porcellanidae.

Phylogeography of Petrolisthes armatus, an invasive species with low dispersal ability.

Theoretically, species with high population structure are likely to expand their range, because marginal populations are free to adapt to local conditions; however, meta-analyses have found a negative relation between structure and invasiveness. The crab Petrolisthes armatus has a wide native range, which has expanded in the last three decades. We sequenced 1718 bp of mitochondrial DNA from native and recently established populations to determine the population structure of the former and the origin of the latter. There was phylogenetic separation between Atlantic and eastern Pacific populations, and between east and west Atlantic ones. Haplotypes on the coast of Florida and newly established populations in Georgia and South Carolina belong to a different clade from those from Yucatán to Brazil, though a few haplotypes are shared. In the Pacific, populations from Colombia and Ecuador are highly divergent from those from Panamá and the Sea of Cortez. In general, populations were separated hundreds to million years ago with little subsequent gene flow. High genetic diversity in the newly established populations shows that they were founded by many individuals. Range expansion appears to have been limited by low dispersal rather than lack of ability of marginal populations to adapt to extreme conditions.

A new species of the genus Petrolisthes Stimpson (Crustacea, Decapoda, Porcellanidae) from the Central Pacific, with remarks and new records for P. aegyptiacus Werding & Hiller.

Petrolisthes paulayi sp. n. is described from specimens collected in French Polynesia. The new species belongs to an assemblage of morphologically similar Indo-West Pacific (IWP) species, here designated as the "mesobranchial-spine group". All species in the group bear carapace spines, including one or more mesobranchial spines, and transverse, piliferous striations on the dorsal surface of carapace and chelipeds. Petrolisthes paulayi sp. n. is distinguishable from all species in the group by its forwardly produced, trilobate front, and a characteristic combination of carapace spines. We also report on the range extension and live coloration of Petrolisthes aegyptiacus Werding & Hiller, another species of the mesobranchial-spine group, so far considered a Red Sea endemic. Specimens from the Mascaréne Islands confirm that the geographic range of the species extends to the southern Indian Ocean. While specimens morphologically similar to Petrolisthes aegyptiacus, and collected in the Line and Society Islands, suggest a large range extension to the Central Pacific, it is probable that these individuals represent an undescribed species closely related to Petrolisthes aegyptiacus.

Description of a new species of Petrolisthes in the Indo-West Pacific with a redefinition of P.hastatus Stimpson, 1858 and resurrection of P.inermis (Heller, 1862) (Crustacea, Anomura, Porcellanidae).

The porcellanid crab Petrolistheshastatus Stimpson, 1858, has been traditionally viewed as a highly variable species with a wide distribution in the West Pacific. For more than a century there has been taxonomic confusion of this species with morphologically similar taxa, some of which were synonymized with Stimpson's taxon. We redefine Petrolistheshastatus, resurrect Petrolisthesinermis as a valid species, discuss the status of Petrolisthestenkatei De Man, 1893, and describe a new species as Petrolistheselegantissimus from Indonesia.

The Petrolisthes galathinus complex: species boundaries based on color pattern, morphology and molecules, and evolutionary interrelationships between this complex and other Porcellanidae (Crustacea: Decapoda: Anomura).

While the amphi-American porcellanid crab Petrolistes galathinus has been traditionally viewed as a highly variable species containing several different color forms, we consider it to be a complex of at least 6 morphologically similar species with similar ecological requirements, but diagnosable through coloration. Here we surveyed sequence variation of the mitochondrial 16S rRNA gene, compared the morphology of adults and of the first larval stage (Zoea I), and explored shape variation of the sternal plate using geometric morphometric methods, to investigate boundaries among the species in the complex, and to confirm the validity of color and color pattern for distinguishing them. Sequences and larval morphological characters of other porcellanids were included to investigate the correspondence between genetic divergence and morphology of adults and larvae. The molecular and morphometric results support the validity of the species in the complex, and of color pattern for their distinction. The close relationship between the complex and the putative ancenstral porcellanid Parapetrolisthes tortugensis was indicated by the molecular and larval-morphology results. The adult morphology of this species is interpreted as a result of convergent evolution driven by a relatively rapid ecological adaptation to conditions in deeper waters. The nesting position in the phylogenetic trees of Petrocheles australiensis outside the Porcellanidae clade questions the monophyly of this family.