Parasites of shore crabs in the genus Hemigrapsus (Decapoda: Brachyura: Varunidae) and their status in crabs geographically displaced: a review

Two brachyurans of the varunid genus Hemigrapsus from the northwestern Pacific Ocean have invaded coastal regions of the north Atlantic – Hemigrapsus takanoi (sibling species of Hemigrapsus penicillatus) and Hemigrapsus sanguineus in Europe and the latter in the USA. Parasites are known from these crabs in their native habitats, but except for an undescribed larval nematode, none has been found in those examined from their new locations. These parasites include metacercariae of eight species of microphallid trematode, the rhizocephalan barnacles Polyascus polygenea, Sacculina nigra and Sacculina senta, and the obligate gut-inhabiting mesomycetozoan Enteromyces callianassae (potential parasite). The following have been identified in four of the other eight Pacific crabs within the genus (Hemigrapsus nudus and Hemigrapsus oregonensis, northern hemisphere; Hemigrapsus crenulatus and Hemigrapsus sexdentatus, southern hemisphere), none of which have been geographically displaced: metacercariae of two microphallid trematodes; cystacanths of three acanthocephalans Profilicollis antarcticus, Profilicollis botulus and Profilicollis novaezelandensis; larval nematode Ascarophis sp.; nematomorph Nectonema zealandica; entoniscid isopod Portunion conformis; mesomycetozoan Taeniella carcini; and nemertean egg predator Carcinonemertes epialti. The likelihood of the displaced species of shore crabs being rejoined with their native parasites or their susceptibility to becoming infected by similar parasites in their new locations is discussed. In future global displacements of parasitized Hemigrapsus species it is possible that their most serious parasites, rhizocephalans and entoniscid isopods, may infect previously uninfected species. For example, the two eastern Pacific species of Hemigrapsus (H. nudus and H. oregonensis) may be vulnerable to the rhizocephalans and may in turn be a source of entoniscids transported elsewhere.     

Rhizocephalans (Crustacea: Cirripedia) from Taiwan

One species of shrimp and sixteen species of brachyuran crabs are parasitized by rhizocephalans in Taiwanese waters. Ten of the crabs have never before been recorded as hosts of rhizocephalans. Eight species of rhizocephalans occur in Taiwan. Four species, Diplothylacus taiwanensis, D. calappae, Sacculina scutigera and S. docleae are new to science. The paper records the first example of simultaneous infection of the same host individual by two rhizocephalan species, and provides further evidence of successive moulting of the external mantle cuticle in several species of sacculinids.     

A report on two large collections of the squat lobster Munidopsis platirostris (Decapoda,Anomura, Munidopsidae) from the Caribbean,with notes on their parasites,associates, and reproduction

The reproduction and parasite associates of the squat lobster Munidopsis platirostris (A. Milne Edwards and Bouvier, 1894) were investigated based on collections made in the Bahamas and Curaçao with grassmat and bundled fishing net traps used to collect sipunculan worms and other small invertebrates. Size of ovigerous M. platirostris was significantly correlated with clutch size for females from both localities but females from the Bahamas produced significantly more eggs (on average 10.1 eggs/clutch) than females from Curaçao (on average 6.6 eggs/clutch). Early embryos of M. platirostris from the Bahamas were 0.74–0.82 mm in diameter, similar to some other species of Munidopsidae as well as Chirostylidae. Two species of crustaceans, another squat lobster and a leptostracan, as well as a limpet mollusc, were collected with M. platirostris in the Bahamas, while a sipunculan was an associated species in a Curaçao collection. One specimen of M. platirostris had an unidentified cryptoniscoid epicaridean isopod, possibly representing a new genus and species. Two specimens of M. platirostris each had one rhizocephalan externa of a species belonging to Lernaeodiscus Müller, 1862 but their morphology does not match that of L. schmitti Reinhard, 1950, the only species in the genus known from squat lobsters in the western Atlantic. Additional materials and tools, such as DNA analysis, are needed to describe these potentially new parasites and we suggest that use of these traps may be an effective method to obtain additional samples.     

Hypersymbioses in the pinnotherid crabs (Decapoda: Brachyura: Pinnotheridae): a review

Members of the brachyuran family Pinnotheridae are nearly all symbionts of other invertebrates; some crabs are parasitic and others are commensal. Most live inside bivalve molluscs or in the tubes or burrows of polychaetes and other marine organisms. Animals living on or in pinnotherid crabs are considered to be hypersymbiotic and are reviewed here. Hypersymbionts are poorly represented within only 26 members (～8.6%) of the Pinnotheridae (20 species in the subfamily Pinnotherinae and six species in the Pinnothereliinae). Parasitic hypersymbionts are as follows: three species of fungi; one cestode larva (undescribed procercoid of Trypanorhynchida); one trematode metacercaria (undescribed Microphallidae); nematode cysts (undescribed); three species of Nemertea (Carcinonemertidae, two undescribed); two species of rhizocephalan Cirripedia (Sacculinidae; plus five or more undescribed potential sacculinid species); epicaridean Isopoda [13 species of Bopyridae (one undescribed) and four species of entoniscids (Entoniscidae, three undescribed)]. Preliminary biological information on undescribed entoniscids is presented. Several mainly incidental hypersymbioses involving ectosymbionts are known primarily from Pinnixa chaetopterana, a symbiont of polychaete burrows. The ctenostome bryozoan Triticella elongata is the only known obligate ectosymbiont in P. chaetopterana, but it also infests five other species of pinnotherids. Some of the other ectosymbionts (all incidental) on P. chaetopterana are stalked ciliates, hydroids, juvenile polychaetes, bivalve molluscs, balanomorph barnacles, harpacticoid copepods and urochordates. Species of ectosymbionts including an ectoproct bryozoan have been reported from other pinnotherid species. Factors influencing our meagre knowledge of hypersymbioses in the Pinnotheridae are discussed, among them the inaccessibility of crab hosts and research emphasis on taxonomy within the family.     

Description of a new species of Asymmetrione (Isopoda: Bopyridae: Pseudioninae) infesting the hermit crab Paguristes tomentosus (Anomura: Diogenidae) from Peru,with a key to species and a review of southeastern Pacific bopyrids

A new species of bopyrid isopod is described from a host hermit crab Paguristes tomentosus collected from Pisco, Peru and assigned to the pseudionine isopod genus Asymmetrione Codreanu, Codreanu and Pike, 1965. This is the second species in the genus with less than 20° asymmetry in females, but agrees with all other species in the genus in having the characteristic “socket” on the propodus of the female's pereopods, and in all characters of the males. A key is provided to the 10 species now in Asymmetrione. New records of an Anathelges sp. from Pagurus villosus collected in central Chile are given but additional material is required to determine whether these specimens represent the eastern Pacific A. thompsoni or the western Atlantic A. hyptius. A review of all the bopyrid species known from the western South American coast, with remarks on their taxonomy and biology, is provided.     

Ectosymbionts of the non‐indigenous Asian shore crab,Hemigrapsus sanguineus (Decapoda: Varunidae), in the western north Atlantic,and a search for its parasites

Over 560 Asian shore crabs, Hemigrapsus sanguineus, collected mainly in the spring of 2005 and 2006 from rocky intertidal locations in southern New Jersey, were examined for epibionts. Small numbers of the sympatric green crab, Carcinus maenas, and the Atlantic mud crab, Panopeus herbstii, were examined for epifauna to compare with H. sanguineus. Blue mussel spat, Mytilus edulis, and the encrusting, cheilostome bryozoan, Conopeum tenuissimum, were the dominant ectosymbionts of the shore crab, with prevalences of 22.2 and 32.1%, respectively; ranges of intensity were 1–146 spat/crab and 1–31 colonies/crab. Both species are incidental symbionts. Larger crabs had higher prevalences and intensities of C. tenuissimum colonies, and these colonies displayed a distinct pattern of attachment to the carapace which seemed to be related to crab morphology and habitat. Much less common was the encrusting, ctenostome bryozoan Alcyonidium albescens, a facultative symbiont species with a prevalence of 3.4%. Other epibionts were the encrusting, cheilostome Membranipora tenuis, the tubicolous polychaetes Hydroides dianthus, Sabellaria vulgaris, and Spirorbis sp., the barnacles Balanus improvisus and Semibalanus balanoides, and unidentified thecate hydroids, all incidental symbionts with prevalences from 0.2 to 3.2%. The total number of known ectosymbionts of H. sanguineus, including additional species found previously in the USA and the western Pacific, is 13. Carcinus maenas and P. herbstii share some of the same symbionts. Rhizocephalan externae were not observed in any of the crab species used in this study, nor were gill parasites or internal parasites found among 248 specimens of H. sanguineus.     

Parasites of the Lessepsian invasive fish Lagocephalus sceleratus (Gmelin 1789) in the eastern Mediterranean Sea

Lagocephalus sceleratus, is a Lessepsian invasive fish species introduced into the Mediterranean Sea through the Suez Canal. This study investigated it as host of parasites. Out of 41 individuals caught from northern and southern locations of the eastern Aegean Sea, nine were found to host parasites. Gnathia sp. praniza larva, an ectoparasite, was associated with severe damage of the primary and secondary structures of the gills and it was found in one specimen (prevalence 2.4%). Regarding endoparasites, Anisakis type I third-stage larvae were found in two specimens (prevalence 4.9%). In addition, adult nematodes of Hysterothylacium aduncum were found in another six specimens (prevalence 14.6%). Lagocephalus sceleratus is a new host for some indigenous parasites, with low host specificity, in the Mediterranean Sea, providing an additional niche for the success and increase of local populations of these parasites and, to our knowledge, this is the first record of L. sceleratus parasites in this area. Whether these parasites can control the invasion success of L. sceleratus needs to be further investigated. However, the low mean intensity of infection found in this study does not support such control.     

Genetic diversity of freshwater crabs (Brachyura: Sesarmidae) from central Jamaica with description of a new species

Jamaica is the only island of the Greater Antilles where freshwater streams are not populated by representatives of the old lineage of freshwater crabs, the Pseudothelphusidae. Instead, a very diverse fauna of endemic sesarmid crabs inhabits freshwater and terrestrial habitats throughout the island, thereby showing complete independence from the sea. They have been reported thriving in bromeliad leaf axils, rock rubble, empty snail shells, caves and mountain streams. Otherwise, the Sesarmidae are typical inhabitants of soft‐sediment littoral habitats like marshes and mangroves. For many years, crabs from Jamaican mountains streams had been considered to belong to a single species, Sesarma bidentatum Benedict . However, recent morphological and molecular studies have shown that crabs from mountain streams of different regions of the island belong to different species. Consequently, four new crab species have been described over the last 10 years. In this study, we give evidence that freshwater streams in central Jamaica also host two different species of crabs. In streams draining to the north we exclusively found the species S. windsor Türkay and Diesel, , while streams draining to the south were inhabited by a closely related but undescribed species of crab. The southern species is here described as new and is referred to as Sesarma meridies sp. n. Morphological and molecular (12S and 16S mtDNA) evidence is provided that allows these two species of freshwater crabs from central Jamaica to be distinguished. The species richness of Jamaican endemic sesarmids thereby increases to 10, which makes the island unique in terms of its diversity of land‐dwelling crabs.     

First record of the genus Gigantione (Epicaridea: Bopyridae: Pseudioninae) from Chinese waters,with description of three new species

The parasitic isopod genus Gigantione is first recorded from China. Four species are reported infesting xanthid and goneplacid crabs, three are new to science, and one is a new record from China. Gigantione ishigakiensis Shiino, 1941 Shiino, S. M. 1941. Further notes on Bopyrids from Kyûsyû and Ryûkyû.. Annotat Zool Jpn., 20: 154–158.  [Google Scholar], infesting Liagore rubromaculata (De Haan); G. hainanensis sp. nov., infesting Atergatis floridus (L.) and Atergatis sp., which differs from other recorded species in the shape of its barbula, first oostegite and subrectangular maxilliped; G. rhombos sp. nov., infesting Heteroplax dentata Stimpson, Eucrate alcocki Serene and Eucrate sp., its female distinguished from other species of Gigantione by having a prominent rhombic projection on the barbula; and G. tau sp. nov., infesting Carcinoplax longimanus (De Haan), the female of which differs from other species mainly by its T‐shaped pigmentation on the head. Four brachyuran crabs are first reported as hosts of bopyrids. A list of all brachyuran species so far recorded as bopyrid hosts in China is provided.     

On three new species of Mesochra Boeck, 1865 (Harpacticoida: Canthocamptidae) from Iceland

Three new species of Mesochra Boeck, 1865, were found during two surveys in south‐western Iceland of the feeding ecology of juvenile lumpsucker Cyclopterus lumpus Linnaeus, 1758, in floating seaweed and the seasonality of harpacticoids in a low intertidal pool. Only two species of the genus, M. lilljeborgi Boeck, 1864 and M. rapiens (Schmeil, 1894), have been found in previous studies in Iceland. The three new species, Mesochra ingolfssoni sp. nov., Mesochra snoppa sp. nov., and Mesochra freyri sp. nov. resemble M. stellfeldi Jakobi, 1954 in the normal (not dwarfed) outer seta of both male and female P5 EXP, but differ in that M. stellfeldi possesses unequal inner baseoendopodal setae on the female P5. The three new species resemble M. pygmaea (Claus, 1863) in the equal inner baseoendopodal setae of the female P5, but differ in the dwarfed outer seta of the male and female P5 EXP present in M. pygmaea, and can be easily separated by shape of the rostrum, female P6, number of pinnate elements on the second antennular segment, general shape of the antenna and shape of the lateral and distal inner spines, among other character states.     

The diets of juvenile horseshoe crabs,Tachypleus tridentatus and Carcinoscorpius rotundicauda (Xiphosura), from nursery beaches proposed for conservation in Hong Kong

Once common as a fishery resource, adult horseshoe crabs of two species occur in Hong Kong. A third, Tachypleus gigas, can no longer be found. Once common too were breeding and nursery beaches for horseshoe crabs in Hong Kong but overfishing of adults, pollution and coastal reclamation have reduced these to but three identified sandy mudflats and only one where juvenile Tachypleus tridentatus and Carcinoscorpius rotundicauda are sympatric. Nothing is known, however, of the conservation requirements of these two species locally and this study of the diets of these juvenile horseshoe crabs on two such nursery beaches aimed at providing information on this most elementary aspect of their biology. Gut contents of juvenile horseshoe crabs, i.e. nine Tachypleus tridentatus (8.5–67?mm prosoma width) and two Carcinoscorpius rotundicauda (50 and 52?mm prosoma width), were analysed and compared with the composition of the ambient assemblage of meiobenthos on a nursery beach at Pak Nai, Hong Kong. The obtained data suggest that juvenile horseshoe crabs of both species are selective benthic feeders and subsist mainly on insect larvae, polychaetes, oligochaetes, small crabs and thin-shelled bivalves. A strong, positive, preference for insect larvae (Chironomous sp.: Diptera: Chironomidae) was recorded, but with no preference for meiofauna over macrofauna.     

Desmosomatidae and Nannoniscidae (Crustacea,Isopoda, Asellota) from bathyal and abyssal depths off North Carolina and their evolution

The deep-sea asellote isopod (Crustacea) species, belonging to the families Desmosomatidae and Nannoniscidae, were studied from R/V Eastward collections of Duke University from three study sites off North Carolina. The Desmosomatid isopod Eugerda svavarssonni n. sp. is described from Site Alpha at 620m. Eugerda latipes Hansen, previously known from boreal North Atlantic, is also reported from this upper slope site. Two new desmosomatid isopods, Mirabilicoxa hessleri n. sp. and M. alberti n. sp., and a new nannoniscid isopod Exiliniscus chandravoli n. sp. are also described from site Beta from 2700 to 3700 m. A nannoniscid isopod Leutziniscus jebamoni gen n., n. sp., and a desmosomatid isopod, Prochelator sarsi n. sp., are described from the deepest study site Omega in the Hatteras Abyssal Plain. A new genus, Nannoniscella is erected to accommodate Nannoniscoides bicustatus Siebenaller and Hessler, 1977. This paper also includes discussions on comparative morphology and sexual dimorphism in species of Mirabilicoxa, zoogeography of species of the genus Eugerda and phylogeny with emphasis on the genus Prochelator.     

Symbiotic associations between hermit crabs and bryozoans from the Otago region,southeastern New Zealand

Thirteen species of bryozoans (six cyclostomes and seven cheilostomes) occurring off the Otago Peninsula (southeastern New Zealand) form symbiotic, possibly mutualistic, associations with hermit crabs. For all but one of these bryozoan species, such an association has not been reported previously. At most only 3 of the 13 bryozoans are obligate symbionts of hermit crabs. Associations are apparently initiated when a bryozoan larva settles on a gastropod shell occupied by a juvenile hermit crab and develops to form a colony which encrusts the whole shell and then continues to grow out beyond the shell aperture in the form of a helicospiral tube. The tube-building bryozoan colony grows in step with the crab, and tube development appears to be controlled by crab morphology and activity. Of the six species of hermit crabs found occupying bryozoan tubes, four were regular tube occupants, although they could also be found in other shelter types. Hermit crabs occupying bryozoan tubes very rarely indulged in shell exchanges or shell fights. There appear to be no clear cut pairwise correlations between hermit crab species and tube-forming bryozoan species. The following bryozoan species are described for the first time: Heteropora parapelliculata, Borgiola otagoensis, Disporella gordoni, Osthimosia monilifera and O. socialis.     

Temporal and seasonal variations in parasites of Metynnis lippincottianus (Characiformes: Characidae), a host from the eastern Amazon (Brazil)

ABSTRACT

This study investigated the influence of temporal and seasonal variation (rainy/dry cycle) on the component community structure and infracommunities of parasites in Metynnis lippincottianus from the eastern Amazon (Brazil). A total of 8,774 parasites representing 9 species and 22,765 parasites representing 12 species was collected in 2011 and 2016 respectively, but only 42.8% of the species were common to both study years. In both years, there was a dominance of Ichthyophthirius multifiliis and the component community was 51% dissimilar. The species richness of parasites and the Berger–Parker dominance were higher in 2016, while the evenness and Brillouin diversity were higher in 2011. The prevalence and abundance of I. multifiliis and P. pillulare, as well as the prevalence of Contracaecum sp. were higher in the rainy season. The abundance of Anacanthorus strongylophalus, Urocleidoides sp., Dadayus pacupeva and Dadaytrema oxycephala was higher in the dry season. Infection with Procamallanus (Spirocamallanus) inopinatus was not influenced by the season, while by Trichodina sp. occurred only in the dry season and Ergasilus xinguensis only in the rainy season. The species richness of parasites, Brillouin diversity index and evenness were higher in the dry season, while the Berger–Parker index was higher in the rainy season. Temporal variation of communities and infracommunities of parasites was influenced by the body size of host populations and increase in anthropogenic impacts. Effect of seasons on environmental quality, host size and availability of infective stages of parasites were the determining factors in structuring the component communities and infracommunities of parasites.     

A review of the genus Scyracepon Tattersall, 1905 (Crustacea: Isopoda: Bopyridae), with description of a new species from China

The parasitic isopod genus Scyracepon Tattersall, 1905 is recorded from China for the first time, and a new species, Scyracepon distincta, is described from the host Jonas distinctus (Brachyura: Corystidae). Females of the new species can be distinguished from those of the other six species of Scyracepon by their subequal mid-dorsal projections on pereomeres 6 and 7 (lacking on other pereomeres) and pleonal segments with medial but not lateral fusion. Males of the new species have the first two pleomeres free, pleomeres 3–5 fused, and bear midventral tubercles on all pereomeres and the first pleomere. This is the first record of any species of Corystidae bearing parasitic isopods. Remarks on, and a key to, the seven known species of Scyracepon are provided.     

A new species of Metatrichoniscoides (Crustacea: Isopoda: Oniscoidea) from the coast of South Wales,U.K.

Summary

A new species of terrestrial isopod, Metatrichonixoides celticus is described and differentiated from other European species of the same genus. M. celticus occurs on the coast of South Wales, U.K. and its supralittoral habitat is outlined.     

Crustaceans associated with the deep-water gorgonian corals Paragorgia arborea (L., 1758) and Primnoa resedaeformis (Gunn., 1763)

To explore the crustacean fauna associated with deep-water gorgonian corals, suction samples were taken from colonies of Paragorgia arborea and Primnoa resedaeformis using a Remotely Operated Vehicle. Seven colonies of P. arborea and eight of P. resedaeformis were sampled from 330–500?m depth in the Northeast Channel off Nova Scotia. A total of 17 species were identified as being associated with the corals. The P. arborea fauna was richer than the P. resedaeformis fauna in both abundance and number of species, with 1303 versus 102 individuals and 16 versus seven species, respectively. However, 13 of the species associated with P. arborea were from hydroids attached to the coral. Amphipods dominated the fauna both in abundance and numbers of species and the most common species were Metopa bruzelii, Stenopleustes malmgreni, Proboloides calcarata and Aeginella spinosa. The isopod Munna boecki and the cirripede Ornatoscalpellum stroemii were also quite common. The most strongly associated crustaceans were two parasitic poecilostomatid copepods; these are common also on tropical gorgonians and are most likely obligate associates. The frequently occurring shrimp Pandalus propinquus probably avoids predation by seeking protection among the coral branches. Shrimp counts from video records showed that visual inspection without physically disturbing colonies will generally not reveal the crustaceans hidden in coral colonies. The galatheid Eumunida picta was observed on P. resedaeformis colonies. The fauna of the deep-water gorgonians corresponded to the fauna of tropical shallow-water gorgonians in the numerical dominance of amphipods and parasitic copepods; however, species richness is higher and decapods, which constitute a rich fauna on tropical gorgonians, were only represented by two species.     

Diet composition of an invasive population of Lithobates catesbeianus (American Bullfrog) from Argentina

The American bullfrog Lithobates catesbeianus has been introduced around the world, with invasive populations reported from almost all South American countries. A population of this species was introduced in the Calingasta department of San Juan province, which is an arid environment in western Argentina. This work provides information on the dietary composition of an invasive population of L. catesbeianus, and compares the degree of dietary overlap between adults and juveniles. Stomach contents of 169 bullfrogs (82 adults and 87 juveniles) were analysed. Adults consumed 40 prey taxa and Hymenoptera (Insecta) was the most numerous prey item (41.8%), followed by Araneae (13.6%) and Aeglidae (13.4%). Juveniles consumed 29 prey taxa and Hymenoptera constituted the highest percentage in prey number (77.2%). The trophic overlap niche index at the same level shows a value of 0.64 overlap in dietary community between adults and juveniles of this bullfrog. Aeglidae was volumetrically the most important trophic item (25.4%), followed by Anura (25.02%). Our results showed that cannibalism in bullfrogs is more common than the consumption of native anurans, coinciding with that reported in other populations of introduced bullfrogs. The high similarity in the diets of both size classes and the association between the size of the predator and prey suggest that the impact caused by bullfrogs throughout their ontogeny is high and probably has an impact on their prey. Freshwater crabs are the main items in the diet of Lithobates catesbeianus in other introduced populations and are usually the most conspicuous at our study site. The crabs in freshwater ecosystems are part of the lowest trophic level in the food chain. The major threats to the southern region’s freshwater crabs include deforestation, farming and exotic species. Lithobates catesbeianus has a generalist diet and high overlap between adults and juveniles.