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Abstract A putative new species of tantulocaridan is reported parasitizing a species of typhlotanaid (Tanaideacea) from the Gulf of Mexico at depths up to 2767 m. The tantulocaridan belongs to Microdajus Greve, 1965, species of which are all known from tanaid hosts in the superfamily Paratanoidea. Tantulocaridan samples included newly settled tantulus larvae, early stages of trunk development and developing males; parasites were found attached to anterior appendages (antennules and pereopods) or bodies of hosts. This material likely represents a new species but the condition and number of available specimens precludes a formal description. The putative new species is most similar to Microdajus aporosus Grygier and Sieg, 1988 and Microdajus tchesunovi Kolbasov and Savchenko, 2010 in having an endopodal seta on each of the sixth thoracopods (lacking in other species). Microdajus tchesunovi is the only described species of Microdajus with males bearing unsegmented sixth thoracopod protopods; this character is also found on the present specimens. Males of the newly reported tantulocaridan can be distinguished from those of M. tchesunovi based on protopod 1-5 morphology and setation of the pits on the cephalothorax (fewer setae in males of the western Atlantic specimens compared to M. tchesunovi). This is the first species of Microdajus reported from the western Atlantic and the first tantulocaridan known from the Gulf of Mexico or northwestern Atlantic.

Abstract Two new species of freshwater crabs of the potamid genus Potamiscus Alcock, 1909 are described from Nagaland State of northeastern India. Potamiscus chizami sp. nov. and Potamiscus mima sp. nov. most resemble two Indian congeners [Potamiscus palelensis Mitra and Waikhom, 2019 and Potamiscus tumidulus (Alcock, 1909)] and a species from Myanmar (Potamiscus whitteni Ng, Hla Htoo and Win Mar, 2020) due to the similar terminal segment of the male first gonopod. Both new species can be distinguished from Po. palelensis by their stouter ambulatory legs, from Po. tumidulus by their more-slender male first gonopod, and from Po. whitteni by their strongly concave lateral margins of the male telson and the straight tip of the male first gonopod. Characters of the carapace, male pleon, male gonopods, and female vulvae are employed to differentiate Po. chizami sp. nov. from Po. mima sp. nov.

Abstract Plesionika edwardsii (J.F. Brandt in von Middendorf, 1851) is a cosmopolitan species that inhabits cold temperate and subarctic waters between 50 and 680 m. In the Azorean region, this is the second most abundant shrimp species and populations remain unexploited. To provide insights into a pristine state that can be useful for comparisons across regions and serve as a benchmark for a potential fishery in the future, we analyzed data collected during shrimp trap surveys in the Azores between 1999 and 2000. Plesionika edwardsii were caught between 100 and 600 m depth, with the biggest catches between 200 and 400 m. Sizes varied from 8.3 to 31.3 mm cephalothorax length (CL). Females were bigger and more abundant than males and predominated at depths up to 300 m. Ovigerous females were caught throughout most of the year, with a peak of abundance during the winter. The size at 50 % maturity was 25 mm CL. High variability in distributional patterns and life-history traits has been observed in our study and when compared with literature from other regions, it is difficult to distinguish which differences are potentially fishing-induced. Future studies should investigate the oceanographic processes associated with P. edwardsii ecology and commercial fisheries should be made on a precautionary basis.

ABSTRACT Ejaculate allocation patterns vary widely among species and often depend on characteristics of the individual. However, it is poorly known whether ejaculate allocation patterns change in response to distinct ontogenetic stages (i.e., adolescent vs. adult). The present study aims to describe the mating process and test variations in ejaculate allocation in response to the ontogenetic stage of the Chilean kelp crab Taliepus dentatus (H. Milne Edwards, 1834). Mating consists of the following sequence: (1) pre-copulatory guarding (i.e., male grasping female and/or caging female between legs), (2) copulation in sternum-to-sternum position, and (3) post-copulatory guarding (i.e., male grasping female or carrying her around by the chelae). The mating behavior and ejaculate allocation pattern differed between the two contrasting male ontogenetic stages. Adolescent males generally delivered less ejaculate in repeated short copulations and adult males transferred more ejaculate in a single extended copulation. Ejaculate allocation in adolescents was dependent on female size, but not so in adults. Variation in the ejaculate allocation pattern may be common in species with contrasting male ontogenetic stages, where less competitive males (i.e., adolescents) economize their limited seminal reserves. Conversely, adults which have a greater capacity to produce seminal material (fluids + spermatozoa) may invest greater quantities of seminal material.

Abstract Considering the environmental impacts to rivers caused by the exploitation of water resources and the consequences of these impacts upon fauna, the objective of this study was to evaluate the population biology of the shrimp Atya scabra (Leach, 1816) in the final stretch of the major river of South America. This species was assessed as “Near Threatened” in the red book of Brazilian crustaceans. Specimens were sampled monthly from February 2015 to January 2016 in a region of the lower São Francisco River, Brazil. A total of 233 individuals of A. scabra were collected, including 120 males and 113 females (71 non-ovigerous and 42 ovigerous). Atya scabra abundance was higher when water flow values increased. A decrease in abundance was observed over the one year of sampling, indicating a decline of about 90 % in this population in this region of the São Francisco River. We suggest that this decline was caused by the reduction of water flow in the São Francisco River, due to a policy that authorized retaining more water behind dams and releasing less water into the river in April and June 2015. In light of this, other studies should monitor the population dynamics of this species, while legislative actions are also needed to protect this fragile ecosystem.

Abstract Fiddler crabs are important components of intertidal benthic macrofauna in estuarine habitats. However, these invertebrates often inhabit areas under anthropogenic-driven changes. In this study, we evaluated the habitat quality and the population biology of the fiddler crab Uca maracoani (Latreille, 1802) in a mangrove area under anthropogenic influence, on the southern coast of São Paulo state, Brazil. Sediment samples for ecotoxicological analyses and data on the population biology of U. maracoani were collected monthly between October 2008 and October 2009. Contamination was observed in sediment samples from all months, indicating that benthic organisms inhabiting the study area are continuously exposed to toxicity. The sex ratio did not deviate from 1:1 for the whole population of U. maracoani, within any given month (except in October 2008, when males outnumbered females). Adult males and females showed a similar size, while juvenile females were larger than juvenile males, probably reflecting that females attained sexual maturity at a larger size than males. For both juvenile and adult stages, the major cheliped propodus length and height in males and the abdomen width in females showed positive allometry. The size-frequency distribution of the studied population varied from unimodal to bimodal. Juveniles were recorded in all months, suggesting the studied population has continuous recruitment. In contrast, ovigerous females were not found in the study area for several months. Although U. maracoani is continuously exposed to contamination present in the sediment, it presents a well-established population and seems to persist in the study area.

Abstract Although the cladoceran Anthalona neotropica Sousa, Elmoor-Loureiro and Debastiani-Júnior, 2015 has a wide geographic range in Brazil, until now, it has only been reported in a few localities. The present study reports the occurrence of this species in the estuaries of the Jequitinhonha River and Una River, representing the first records of An. neotropica in Bahia State, Brazil.

Abstract Despite the rising interest in cladoceran biogeography worldwide, many species distributions are still unknown to science, especially in naturally rich freshwater of the Neotropics. Herein we present a checklist of the taxa, giving the distributions of the valid species throughout 13 hydrographic basins within the two freshwater ecoregions of Northeastern Mata Atlântica and São Francisco. Superorder Cladocera comprises 72 known species in Bahia State classified into two orders: the Anomopoda, represented by Chydoridae (36 spp), Daphniidae (7), Macrothricidae (6), Bosminidae (4), Moinidae (3) and Ilyocryptidae (2); and Ctenopoda, represented by Sididae (8 spp). Species from the orders Onychopoda and Haplopoda are still lacking in Neotropical waters. The first compilation of the data on the Cladocera of Bahia, Brazil, is represented by this checklist and contains 38 new records for the state. Critical remarks on species distributions, as well as detailed information on sampling sites and geographic coordinates are also included.

Abstract A new genus and two new species of potamiscine freshwater crabs (Potamidae) are described from the Abor Hills in the Upper Siang District of Arunachal Pradesh State, northeastern India. Abormon gen. nov. is morphologically most similar to Pararanguna Dai and Chen, 1985, from Yunnan Province in China but can be differentiated by the setose dorsal surface and the medially concave posterolateral margins of the carapace, the concave lateral margins of the male telson, the relatively low dorsal flap on the terminal segment of the male first gonopod, and the anteriorly open and transversely ovate vulvae. Abormon capillosum sp. nov. can be distinguished from A. praecalvum sp. nov. by characters of the carapace, pereiopods, male pleonal somite 6, male gonopods, and vulvae.

Abstract The family Pseudorhombilidae Alcock, 1900 is widely distributed in the tropical western Atlantic, occurring from shallow waters to the continental slope, inhabiting sandy, gravelly, or muddy substrates. Despite the broad distribution of this family in the Americas, the species Pseudorhombila octodentata Rathbun, 1906 and Pseudorhombila quadridentata (Latreille, 1828) have been observed only in a few localities, with disjunct records, and Robertsella meridionalis Tavares and Gouvêa, 2013 has been recorded only in one type locality (Santa Catarina, Brazil). The present work reports new occurrences of P. octodentata from the state of Sergipe and P. quadridentata from the state of Amapá, and the second occurrence of R. meridionalis from the state of Rio Grande do Norte, Brazil. These new records are an important contribution to the understanding of distributional patterns of pseudorhombilid crab species in Brazil and to the increase in biodiversity data of crustaceans from the North and Northeast regions of Brazil.

Abstract Atya gabonensis Giebel, 1875 and Atya scabra (Leach, 1816) are amphidromous shrimps. In some areas, these species populations are vulnerable due to the anthropogenic impact on their habitats and commercial exploitation. However, basic morphometric data is still lacking. This study provides morphometric data on both species in the Fluvial Island Domain of Paraíba do Sul River basin, Brazil. Sampling was performed bimonthly from January 2013 to March 2014. Individuals were analysed according to sex, weight, carapace length and width, abdomen length, second abdominal pleura height and width, length of third pereopod articles, and length and width of the male appendix interna. We sampled 42 individuals of A. gabonensis and 16 individuals of A. scabra. In both species, females showed abdomen and second abdominal pleura larger than males, while males showed third pereopod articles larger than females, both related to sexual dimorphism. We detected differences in the carapace length × carapace width relationship and in the growth pattern of the male appendix interna between species, with A. gabonensis presenting the carapace and the male appendix interna wider than A. scabra. Morphometric aspects of both species are unpublished for this region, and this data is valuable for A. gabonensis in the western Atlantic and for A. scabra from Rio de Janeiro state. Such information is essential for future systematic assessment and establishment of conservation management policies.

Abstract Clausidium Kossman, 1874 is a genus of copepods that is found in subtropical to temperate coastal areas. All species of the genus occur on the bodies of mud shrimp of the families Callianassidae and Upogebiidae. Based on morphological data from light scanning and confocal laser scanning microscopy, there are four species of Clausidium copepod in Iran. In this study we address Clausidium iranensis Sepahvand, Kihara and Boxshall, 2019 and Clausidium persiaensis Sepahvand and Kihara, 2017 that were reported on the body of the burrowing shrimps Neocallichirus jousseaumei (Nobili, 1904) and Callianidea typa Milne Edwards, 1837, respectively. We undertook analyses of mitochondrial DNA gene sequences (CO1) to evaluate taxonomic status and taxonomic relationships of the Clausidium species. The result demonstrates that two major clades, with strong support, can be identified within the Clausidium copepods in the southern waters of Iran, representing distinct taxonomic entities at the species rank. Our data indicate that CO1 can be a powerful tool for species identification and delimitation. In the case of Clausidium copepods, the general utility of CO1 for taxonomic relationship inferences within a genus or a family is still under investigated. Our study adds the first genetic data from these copepods from the Persian Gulf and Gulf of Oman.

Abstract Santaremicaris gen. nov. is proposed to accommodate Santaremicaris amazonensis sp. nov., a new species collected by Noodt from the hyporheic zone of the Amazonas River at Santarém, Brazil, and Parastenocaris santaremensis Noodt, 1963, which is redescribed and designated as the type species of the new genus. The new genus is recorded also from several localities of the Amazonian hydrographic basin. Santaremicaris gen. nov. is well supported by clear autapomorphies, e.g., 1) the absence of distal spinules on the endopod of the second swimming leg of the male, which is ornamented with strong outer spinules along the first 2/3 of the segment and armed with a long distal seta the insertion area of which covers almost the whole width of the segment; 2) the presence of a triangular, short and strongly sclerotized endopod on the fourth swimming leg of the male; and 3) the presence of a long and slim male fifth leg ending in a long distal spiniform process, with irregular margins, armed with only three setigerous elements on the outer margin, and reaching the middle of the subsequent urosomal segment or beyond it. The new genus is closely related to Murunducaris Reid, 1994, with males sharing conspicuous ornamentation on the inner margin of the first swimming leg basis, represented either by an enlarged spinule accompanied by minute accessory spinules or by a row of strong spinules. In addition, the males of both Murunducaris and Santaremicaris gen. nov. share an enlarged intercoxal sclerite with a median process on the fifth leg.

Abstract Spawning season, recruitment, and growth of the freshwater prawn Macrobrachium lamarrei were studied in a perennial wetland, northeastern Bangladesh during October 2016 to September 2017. Spawning season was estimated based on the monthly variations of percent ovigerous females. Recruitment and growth were estimated using the time series of the length-frequency distributions. We compared the von Bertalanffy growth function (VBGF) and the Pauly and Gaschütz growth function (PGGF) to identify any seasonal oscillation in growth rate. Ovigerous females occurred almost throughout the year, indicating a prolonged spawning season with two peaks between March-April (minor peak) and June-September (major peak). Both males and females with modal size ~ 8.0 mm carapace length first recruited in October, which synchronized with the major peak spawning season. There was seasonality in growth rate; hence, PGGF was adopted as the best-fitting model to describe the growth of both sexes. The estimated equations were Lt = 17.86 (1- exp [-2.432 (t/12 - 0.072) - (1.766/2π) sin {2π (t/12 - 0.982)}] for males and Lt = 23.18 (1- exp [-1.342 (t/12 + 0.106) - (0.388/2π) sin {2π (t/12 - 0.209)}] for females. Sexual dimorphism was found with larger size in females than males. Longevity was estimated to be ~ 14 months for both sexes. These findings can be useful to formulate management measures for this prawn.

Abstract A new species of the pinnotherid crab genus Austinixa from La Cruz de Huanacaxtle, Nayarit, Mexico is described. The new species is closely related to Austinixa roblesi Palacios Theil and Felder, 2020, however these can be distinguished mainly by the shape of the male pleon and telson, gonopod and chelae. In addition, four new records of distribution of Austinixa felipensis Glassell, 1935 are added. The species is known previously from the type locality to the north of the Gulf of California and the Pacific coast of El Salvador and Nicaragua. The new collection sites are located on the eastern coast of the Gulf of California and the states of Nayarit and Jalisco, Mexico.

Abstract Temporary pools are freshwater bodies of significant interest due to their high species diversity, and the colonization and extinction processes observed at temporal scales. The aim of the present study was to perform a short-term ecological comparison in a group of shallow temporary pools in northern Chilean Patagonia in two periods, August and September 2018. The results revealed marked differences in terms of species richness in the study pools at different conductivities and chlorophyll a concentrations. The dominant species was the calanoid copepod Boeckella gracilis Daday, 1902, while the presence of the rare Anostracan Branchinecta rocaensis Cohen, 1982 was reported in conditions of low chlorophyll a and low conductivity. The community was studied using co-occurrence null models that revealed the absence of structured patterns in species associations, and the presence of niche overlap, with many repeated species that have a similar ecological niche. The present results are identical with observations from temporary pools in southern Chilean Patagonia.