Non-ovigerous Females Research Articles

Spatial distribution patterns in biomass and population structure of the deep sea red crab Chaceon notialis in the Southwestern Atlantic Ocean

Spatial heterogeneity is a conspicuous feature in life history traits of the deep sea red crab Chaceon notialis in the Southwestern Atlantic Ocean. However, a quantitative assessment of its spatial distribution in Uruguayan waters is lacking. A fishing survey was conducted in 2005 between latitudes 35°00′S and 37°00′S, water depth ranging from 300 to 1600 m. A likelihood-based geostatistical approach showed a persistent spatial structure of the red crab for both the whole population and the harvestable stock, with global biomass estimates of 55,054 t and 34,870 t respectively. Similar estimates were provided by the “effective fishing area” technique (53,800 t and 36,400 t, respectively). C. notialis showed clear large-scale patterns: (1) concerning latitude, the highest density and CPUE were found between 35°40′S and 36°20′S. Males were mainly concentrated between 35°20′S and 36°00′S, whereas the relative representation of both ovigerous and non-ovigerous females increased at the northern end of the study area. Male individual weight increased asymptotically towards higher latitudes, while females followed the reverse pattern. (2) Bathymetric analysis showed the highest density and CPUE at depths close to 900–1100 m, coinciding with the highest representation of males. By contrast, females mainly occurred in shallower waters (300–500 m), and ovigerous females only between 300 and 400 m. Individual weight of males and females consistently decreased from 300 to 1600 m. Proportion of molting males increased with latitude and depth, whereas molting females followed the reverse trend. Spatially explicit management tools are suggested, including fishing closures between 300 and 500 m depth and between latitudes 35°00′S and 35°40′S (main spawning area with the highest proportion of females) and at depths > 1200 m (recruitment area).

Swimming kinematics of Eurytemora affinis (Copepoda, Calanoida) reproductive stages and differential vulnerability to predation of larval Dicentrarchus labrax (Teleostei, Perciformes)

In egg-bearing copepods, the ovigerous females are reported to be more vulnerable to predators. However, the underlying mechanistic details of increased vulnerability are not yet well understood. We studied the predator-prey interaction between the copepod prey Eurytemora affinis and a predator, post-larvae of the sea bass Dicentrarchus labrax. Standard video techniques have been used to quantify the predation efficiency of larval sea bass and to record the two-dimensional swimming behavior of the different reproductive stages (males, non-ovigerous females and ovigerous females) of E. affinis in both the absence and presence of predators. Our results revealed that ovigerous females suffered higher mortality rates than either non-ovigerous females or males. Body size and swimming speed seemed to be the main determinants of prey conspicuousness to predators. In the light of published data, we conclude that acute vulnerability of E. affinis ovigerous females to planktivorous predators is not necessarily harmful at the population level.

Absence of a prezygotic behavioural barrier to gene flow between the two sympatric morphs of the squat lobster Munida gregaria (Fabricius, 1793) (Decapoda: Anomura: Galatheidae)

Munida gregaria and M. subrugosa have been considered two different species for more than a century; however, after a recent molecular phylogenetic study, they are considered a single polymorphic species. Yet, the use of markers to diagnose species may be misleading when divergence between species is recent, since a speciation event may be obscured by the retention and stochastic sorting of ancestral polymorphisms. The morphs gregaria and subrugosa of Munida gregaria constitute an interesting case for the study of behavioural isolation since they are sympatric, breed at the same time of the year, and might have experienced a recent speciation. Mating behaviour observations and mate choice mating trials were conducted in order to investigate the potential existence of a behavioural prezygotic barrier to gene flow between these two morphs. Since factors involved in mate choice in galatheids are unknown, the four possible combinations of the two different morphs in trios were used to test for the existence of mate choice. Video recordings of all the possible trio combinations revealed that there was cross-attraction between males and females of different morphs. Females bearing partial broods participated in encounters as well as non-ovigerous females. The frequency and duration of homo- and heterotypic encounters were registered, and a reproductive isolation index was calculated for each variable for each trio. The isolation indexes calculated were not different from zero indicating random mating, and were not affected by the composition of the trio or the partial ovigerous condition of females. These results provided evidence of the absence of behavioural prezygotic barriers to gene flow between the morphs gregaria and subrugosa of M. gregaria.

Food and Feeding of the Blue Swimmer Crab, Portunus Pelagicus (Linnaeus, 1758) (Decapoda, Brachyura) along the Coast of Mandapam, Tamil Nadu, India

AbstractFood habits of the blue swimmer crab, Portunus pelagicus were investigated using specimens collected from trawl catches in the Mandapam region, Tamil Nadu, along the east coast of India (9°20-25′N 79°5-10′E), during the period January to December, 1999. The stomach contents of 452 crabs, ranging from 61 to 180 mm carapace width, were analysed. Their diet included crustaceans, molluscs, fishes, unidentifiable matter, and debris. In adult crabs, crustaceans constituted the dominant food source and these were present in 78.43% of the stomachs analysed. The stomach contents of juveniles and sub-adults were dominated by debris. There was no significant difference between sexes in the frequency of occurrence of food items or in their “percentage points” [= the (virtual) percentual contribution to the fullness of a 100% full stomach]. However, there was a difference between the stomachs of ovigerous and non-ovigerous females. There were also significant differences in the preference for food items in the different size groups of the crab. The results collected from the present study showed that P. pelagicus exhibits, in this region at least, a clear preference for crustaceans.

Density, distribution and population structure of Opusia indica (Ocypodoidae: Camptandriidae) in a coastal mangrove creek in Pakistan

The density, distribution and population structure of Opusia indica were studied through transects method. Two transects were delimited in a mangrove area of Korangi creek (24°79′ N/67°20′ E). On each transect, three 0.25 m2 quadrats were sampled at three tidal levels on a monthly basis during low tide. A total of 1919 crabs were obtained, of which 775 were males, 945 were non-ovigerous females and 199 were ovigerous females. Density of crabs varied between 198 m−2 to 798 m−2. The density and size distribution showed significant difference from low tide level to high tide level and were positively correlated with the percent moisture, percent organic matter and sediment structure. Based on carapace width (CW) males were significantly larger than the females indicating sexual dimorphism. The monthly size frequency distribution of crabs showed recruitment of juvenile crabs (< than 4 mm) nearly throughout the year except in few months. The monthly sex ratio deviated from 1:1 throughout the year, with female bias (χ2 = 31.633, P = 0.001 and df =11). Breeding was seasonal with peaks in SW monsoon. Size at sexual maturity based on smallest ovigerous female was CW = 4.0 mm. The average number of eggs per female were 2066 ± 479 (n = 25). Positive linear relationship was observed between the size of the female crabs and the egg numbers (r2 = 0.554).

Ovigerous Female Amphipods (Gammarus pseudolimnaeus) Face Increased Risks from Vertebrate and Invertebrate Predators

ABSTRACT We investigated the mortality rates of male and female amphipods resulting from stickleback fish Culaea inconstans) and dragonfly nymphs (Basiaeschna janata) predation. Both predators consumed significantly more ovigerous female amphipods than non-ovigerous females or males in 24-h trials. Stickleback fish consumed more non-ovigerous females than males, whereas dragonflies consumed more males than non-ovigerous females. These results were consistent across trials conducted under ambient light-dark regimes and those conducted in the absence of light, although overall mortality rates were highest in light trials. There were no significant differences in the recorded behaviors of the two predators. However, the behavior of ovigerous females differed significantly from that of males and non-ovigerous females, which may help to explain the overall differences in mortality. These results suggest that female amphipods incur a significant cost of increased predation risk associated with maternal care.

More common than reported: range extension, size–frequency and sex-ratio of Uca (Minuca) victoriana (Crustacea: Ocypodidae) in tropical mangroves, Brazil

The fiddler crab Uca (Minuca) victoriana von Hagen, 1987 has been reported, until recently, only from the type locality at Vitoria, State of Espirito Santo, Brazil. We report here, for the first time, the occurrence of U. (M.) victoriana in estuaries of the States of Bahia and Pernambuco, north-eastern Brazil, extending its distribution; as well as some aspects of its population biology. For the population study, four sites were defined in mangroves of the Mamucabas and Ariquinda Rivers, Pernambuco, on different types of substrate, and sampled monthly during spring low tide from April 2008 through to March 2009. A total of 41 specimens were obtained in June 2008 in the Arinquinda River, of which 25 were males, 16 non-ovigerous females and 1 ovigerous female. In the Mamucabas River, 772 crabs were collected over the year, including 472 males, 300 non-ovigerous females and 2 ovigerous females. In both areas, the U. (M.) victoriana population showed a unimodal size–frequency distribution, with males and females (ovigerous and non-ovigerous) similar in size (7.46 ± 1.60 mm for males and 7.09 ± 1.45 mm for females; t = −0.744; P > 0.05). The overall sex-ratio (1:1.57) differed significantly from the expected 1:1 proportion1 (χ2 = 38.32; P U. (M.) rapax and U. (M.) burgersi . Some morphological characters to distinguish among these species are presented.

Infestation of the squat lobster Munida gregaria (Anomura: Galatheidae) by Pseudione galacanthae (Isopoda: Bopyridae) in San Jorge Gulf, Argentina

We estimated the prevalence of the bopyrid Pseudione galacanthae parasitizing the population of the squat lobster Munida gregaria in San Jorge Gulf and analysed some aspects concerning the effect of the parasite on host reproductive potential. The relationship between the development stages of the parasite and the host size was also analysed. The squat lobsters were caught as by-catch in the coastal area of the gulf from vessels operating in the fisheries of hake Merluccius hubbsi, southern king crab Lithodes santolla and Argentine red shrimp Pleoticus muelleri. The samples were collected between October 1997 and June 2009. In the laboratory, squat lobsters were sexed and the length of their carapace was measured. In males, the length of the right cheliped was recorded and gonadal development was examined. In females, the size and number of carried eggs were determined and the length of the pleopods III, IV and V were measured. All squat lobsters parasitized exhibit a gross bulge in the right side of carapace. Prevalence ranged between 0 and 1.43% (N = 21,519). No significant differences in prevalence were found for sexes, depths and seasons. The prevalence was higher for the size interval 7–10 mm CL (0.79%) than for the rest of the intervals. Parasitism had no effect on the secondary sex characters. Parasitized males displayed gonad development. There was no difference in prevalence between ovigerous and non-ovigerous squat-lobster females. Parasitized females had smaller eggs than non-parasitized ones, but their fecundity was similar. The linear relationship between the parasite and host sizes and the presence of larvae and immature stages of P. galacanthae in small-sized squat lobsters suggest that the host is infected early in its development. The low prevalence could be related to oceanographic conditions which favour larval dispersal of the parasite and host. The infestation by P. galacanthae has little impact on the M. gregaria population, mostly due to the low prevalences of infestation and the minor impact in reproductive function.

Epibionts on Arenaeus cribrarius (Brachyura: Portunidae) from Brazil

Mean prevalence and intensity of infestations by epibionts were evaluated in Arenaeus cribrarius (Lamarck, 1818), based on monthly samplings (May/1991 to April/1993), in Ubatuba, Brazil. Bryozoans were quantified in terms of colony numbers and barnacles by the number of specimens. Prevalence of infestation was determined in 1,914 individuals of A. cribrarius and assessed with respect to sex, maturity stage and season. No significant interaction was detected between epibionts and biological host factors. Males showed a higher infestation rate by Chelonibia patula (Ranzani, 1818) when compared to mature non-ovigerous females, yet Octolasmis lowei Darwin, 1851 infestation was associated to adult crabs. The ovigerous females of A. cribrarius showed a higher prevalence of infestation than males and non-ovigerous females, with lower infestations being recorded during winter. A synchrony between the life cycle of the epibionts and their hosts was evident and promotes the continuity of the former in the area.

How does salinity influence the swimming speed of the estuarine calanoid copepod Eurytemora affinis?

Michalek et al. (Michalek et al., 2010) report that, in the absence of food, increase in salinity (i.e. 5, 15, 25 and 30) steadily decreased the instantaneous speed of Eurytemora affinis reproductive stages (male, non-ovigerous female and ovigerous female). This contradicts previous observations conducted on individuals obtained from a laboratory culture in the presence of food, i.e. a mixture of Isochrysis galbana and Nanochloropsis oculata, showing an increase in overall swimming activity, speed and path complexity for males and non-ovigerous females, but not for ovigerous females (Seuront, 2006). To account for this discrepancy, Michalek et al. (Michalek et al., 2010) stressed the importance of the experimental conditions employed for observations, but barely discussed the implications of their findings in an ecological context as was done by Seuront (Seuront, 2006, see their Figure 6). It is agreed that it is difficult to compare behavioural responses of copepods originating from a continuous culture (Seuront, 2006) and from the field (Michalek et ...

Reproductive period and size at the onset of sexual maturity of mottled purse crab, Persephona mediterranea (Herbst, 1794) (Brachyura, Leucosioidea) on the southeastern Brazilian coast

The reproductive biology of Persephona mediterranea was investigated in relation to the following aspects: population structure, size at the onset of sexual maturity, sexual size dimorphism, and reproductive period. A total of 1,283 specimens were obtained (565 males, 120 non-ovigerous females and 598 ovigerous females). CW50 values were 22.8 and 22.3 mm CW for males and females, respectively, and the mean size of males was significantly larger than that of females. Persephona mediterranea shows continuous reproduction. However, there is a reduction in the proportion of ovigerous females and males with gonads in advanced developmental stage during the autumn and beginning of the winter. There was no significant correlation between the reproductive activity and variation in abiotic factors. Of the total captured specimens, 98.99% were sexually mature, which may indicate a differential spatial distribution among the distinct age groups, and sampling sites are probably areas occupied by adult individuals of this population.

Some biological aspects of the portunid crab Charybdis natator from the Gulf of Suez, Red sea

he population of the portunid crab Charybdis natator in the Gulf of Suez, Red Sea was studied by monthly sampling from September 2007 to May 2008. Crabs were sexed, measured and berried females recorded. A total of 498 individuals were obtained, of which 232 (46.6%) were males, 212 non-ovigerous females (42.5%), and 54 (10.9%) ovigerous females. The overall sex ratio (M:F) was (1:1.1) and females outnumbered females during September-November. The population showed sex differences in the size frequency distributions, with males reaching larger size than females (70-148.4mm and 47.5-130.5mm CW, respectively). Ovigerous females existed all year round and ranged in size between 83-118.4mm CW. Fecundity ranged from 45230 to 335529 eggs per female and was positively correlated with body size. The effectiveness of the closed season that runs in the Gulf of Suez on the population of C. natator was discussed.

Sexual ratio, reproductive period and seasonal variation of the gonochoric shrimp Hippolyte obliquimanus (Caridea: Hippolytidae)

Hippolyte obliquimanus is a small, gonochoric shrimp found in algal substrates along the western Atlantic coast of Brazil, particularly in association with seaweed of the genus Sargassum. We studied population features (sexual ratio, reproductive period and temporal distribution) of H. obliquimanus in southeastern Brazil, including its relationships with the seasonality of banks of this alga. Specimens were collected at two-monthly intervals from March 2005 to January 2006, in Ubatuba Bay. The sex of individuals was checked, and the carapace length measured. In total, 668 individuals were collected: 211 males (0.70–2.50 mm carapace length), 341 non-ovigerous females (0.55–2.90 mm), and 116 ovigerous females (1.55–3.20 mm). Hippolyte obliquimanus showed seasonal–continuous reproduction and variable continuous recruitment. The highest number of animals (75%) was collected in fall–winter. The percentages of ovigerous females/total females (fall–winter: 27%; spring–summer: 26%) and the sexual ratio (fall–winter: 31%; spring–summer: 32%) were practically equal in both periods. The sexual ratio showed a predominance of females in almost all size classes, and we detected a new sex ratio pattern for this species. The seasonal variation in the number of individuals can be related to its migration to deeper areas, due to the decrease in the abundance of Sargassum sp. in shallower waters in spring–summer.

Differences in behavioral responses of Eurytemora affinis (Copepoda, Calanoida) reproductive stages to salinity variations

Estuarine copepods experience strong and frequent salinity variations caused by alternating tides. Salinity is known to be a major parameter in the ecology of copepods from brackish waters but its effects on small scale behavior are relatively unclear. In this study, we used two-dimensional laboratory filming techniques to record swimming paths of the three reproductive stages (i.e. male, non-ovigerous female and ovigerous female) of Eurytemora affinis from the Seine estuary, under different salinity conditions. We show that the probability density of both the instantaneous swimming speed and the duration of the two most frequent swimming states (i.e. break and slow swimming) followed a power-law trend regardless of the salinity. Increase in salinity (i.e. 5, 15, 25 and 30) steadily decreased the instantaneous speed of E. affinis reproductive stages. At the extreme salinity of 0.5, the mean speed decreased for non-ovigerous females and ovigerous females but increased for males, when compared with higher salinities. Maximum speed was observed at salinity 0.5 for males and at salinity 5 for non-ovigerous females and ovigerous females. Low swimming speeds were associated with break events of high frequency and long duration. High swimming speeds were exhibited with cruising states of high frequency and break events of short duration. This supports laboratory and field studies indicating a preference of E. affinis for low to medium salinities.

Competing for last place: Mating behaviour in a pill-box crab, Halicarcinus cookii (Brachyura: Hymenosomatidae)

The mating strategy of Halicarcinus cookii was investigated to ascertain how males maximised their fitness through mate choice. An intertidal population at Kaikoura, New Zealand, was dominated by mature crabs of both sexes in summer and by immature crabs in the colder months. More than 95% of mature females were ovigerous with early stage and late stage broods found in almost every month, indicating that egg production and larval release is continuous. The operational sex ratio was less than 1 male/female in summer, but often more than 1.0 in the colder months. The gonosomatic index increased along with brood development so that as soon as zoeae were released, the next clutch of eggs was ready to be fertilised. Males searched for receptive females and began pre-copulatory mate guarding without any courtship display. They mated preferentially with late stage or non-ovigerous females: copulation duration was longest for stage 5 females as was post-copulatory guarding (mean 18.3 h). Late stage females were up to 14% of the female population. Mate attraction seems to be the result of an ovarian signal rather than from the developing brood. Manipulation of the sex ratio had effects upon copulation duration and post-copulatory guarding: presence of a rival male increased duration of guarding. Females showed precocious mating in the penultimate instar and were able to lay fertilised eggs after their pubertal moult in the absence of males. H. cookii females have many mates, but males attempt to ensure paternity by preferentially pursuing mature females close to egg laying and by guarding these females after copulation. These behaviours are all elements of a competitive strategy to ensure that a male loses (not wins) the race to copulate because females have a ventral seminal receptacle, giving sperm precedence to the last male to mate. Male mating behaviour is a consequence and evolutionary response to female morphology.

The different aspects in motion of the three reproductive stages of Pseudodiaptomus annandalei (Copepoda, Calanoida)

Individual variation in morphology is linked to organism displacement in numer-ous taxa. This relationship among adult copepods has previously received littleattention. In this study, we questioned whether the swimming behaviour of threemorphologically different adult states of Pseudodiaptomus annandalei (i.e. males, non-ovigerous and ovigerous females) could be differentiated. Two-dimensional videoobservations revealed that some swimming patterns were common to all adultstates, whereas others were more specific to one of the adult states. Males swim ina straight way, ovigerous females exhibit jerky swimming behaviour, and non-ovigerous females exhibit slow and steady gliding, interrupted occasionally byjumps. Direct measures of the swimming behaviour (i.e. mean, maximal and prob-ability density of speed) for a large number of trajectories were considered first.Deeper comparisons of each sexual state were conducted using scale-dependant(i.e. net-to-gross displacement ratio), scale-independent (power spectrum, multi-fractal) metrics and symbolic analysis. The combined analysis emphasized thedifferences (e.g. male swimming patterns were slower and less complex, both ovi-gerous and non-ovigerous female swimming patterns were faster and morecomplex) and similarities (e.g. all swimming patterns were different from theBrownian motion) between adult swimming patterns. The multi-fractal approachidentified differences between the two sexes suggesting differential swimming be-haviour. In an ecological discussion, we relate these differences to mating andpredator avoidance strategies.KEYWORDS: swimming behaviour; sexual dimorphism; calanoid copepod;Pseudodiaptomus annandalei

Distribuição temporal do ermitão Clibanarius vittatus (Anomura, Diogenidae) no litoral do Paraná

Um estudo sobre a flutuação temporal da estrutura populacional do ermitão Clibanarius vittatus (Bosc, 1802) foi realizado no Baixio Mirim, Baía de Guaratuba, Estado do Paraná, Brasil (25°52'S, 48°36'W). Clibanarius vittatus é uma espécie largamente estudada, entretanto estudos da biologia populacional desta em diferentes regiões são escassos. Coletas mensais foram realizadas na zona entremarés, de abril/2005 a março/2006. Foram obtidos 1187 ermitões, dos quais, 949 machos, 22 indivíduos intersexo, 204 fêmeas não ovígeras e 12 fêmeas ovígeras. O comprimento do escudo cefalotorácico (CEC) foi medido e agrupado em 10 classes de tamanho. Machos ocorreram em 10 classes de CEC, enquanto fêmeas e intersexos em apenas seis. A razão de sexos total e mensal foi a favor dos machos. Todas as categorias demográficas estiveram presentes o ano inteiro, com exceção dos intersexos e das fêmeas ovígeras. Estas foram pouco frequentes e ocorreram do final da primavera até o outono, e em agosto de 2005. O período reprodutivo foi considerado contínuo-sazonal, com maior intensidade nos meses mais quentes. A razão de sexos nesta população, que é diferente das demais estudadas, corrobora a teoria de migração proposta para esta espécie. O presente estudo constitui o primeiro registro do período reprodutivo desta espécie em águas rasas de clima subtropical quente.

Infestation rates of the pedunculated barnacle Octolasmis lowei (Cirripedia: Poecilasmatidae) on the spider crab Libinia spinosa (Decapoda: Majoidea)

The prevalence and infestation intensities of Octolasmis lowei in the branchial chambers of Libinia spinosa were evaluated according to the host's sex, size, and moult condition. Epibionts were classified as cyprid larvae, non-ovigerous or ovigerous according to their developmental stage. A median intensity of infestation of 21 epibionts/host was found (range = 1–644; Q3 = 81). Epibiont prevalence values (88%) were higher on ovigerous female hosts than on males (55%) or on non-ovigerous females (31%). Intensity of infestation was positively correlated with host size in both sexes for non-ovigerous and ovigerous epibionts. No preference between host sex by cyprid larvae was observed, nor any correlation between cyprid abundance and host size. Cyprid larvae abundance was positively correlated with settled epibionts on both host sexes. The duration of the intermoult phase was the main factor linked to the establishment of sessile epibionts. These observations are important in relation to crabs that have a terminal moult, because these animals cannot eliminate their epibionts in future moults, thus increasing the importance of density-dependent mechanisms on epibiont establishment; in that way, prevalence of infestation alone can underestimate the real impact of infestation on the host's life cycle.

Population biology and reproduction of the hermit crab Clibanarius vittatus (Decapoda: Anomura) in an estuarine region of southern Brazil

The population dynamics and reproduction of the hermit crab Clibanarius vittatus were evaluated on Pescadores Beach, located on the estuarine channel of São Vicente (São Paulo), Brazil. The hermit crabs were captured by hand during low tide, from May 2001 to April 2003. A total of 2554 hermit crabs were captured, of which 701 were males, 1741 non-ovigerous females, 48 ovigerous females and 64 intersex individuals. The size–frequency distribution of the males was represented by a platykurtic bell-shaped curve, which differed from the leptokurtic bell-shaped curve of the females. The smaller and intermediate classes were composed mainly of females (modal size 6.5–7.5 mm carapace shield length (CSL)), and the larger classes only by males (modal size 9.5–10.5 mm CSL). The overall sex-ratio was skewed toward females (0.39:1/M:F), differing significantly from the expected 1:1. A seasonal reproductive pattern was recorded for C. vittatus in this location, with more intensive reproductive activity in the warmer months. The absence of juveniles suggests that their recruitment area is different than the area inhabited by adults, possibly another area with more protection and specialized or different resources for young.

Use of pleopod morphology to determine sexual dimorphism and maturity in hermit crabs: Isocheles sawayai as a model

In the Anomura, studies on growth patterns are infrequent, possibly because the heterogeneity of the group, especially in terms of morphology, makes it difficult to construct generalized growth models. Particularly hermit crabs are an interesting group to evaluate aspects of growth, because of their unique body. Isocheles sawayai, a hermit crab found only in the western Atlantic Ocean, poorly known with respect to its sexual dimorphism and maturity, was investigated here based on morphometry. Monthly collections (July 2001 through June 2003) were made from a shrimp fishing boat in the Caraguatatuba region on the northern coast of the state of São Paulo, Brazil. The specimens were measured and weighed, and had their sex checked. Throughout the sampling period, 374 specimens of I. sawayai were collected (11.23% nonovigerous females, 6.69% ovigerous females, 79.41% males and 2.67% intersexes). The size at which morphological sexual maturity was reached by both sexes ranged from 4.0 to 4.3 mm shield length, according to the relative growth and the size of the smallest ovigerous female. Sexual dimorphism was shown by males, which were significantly larger than females, and by differences in growth pattern between the sexes, especially for relationships that involved the pleopods, which is related to their different functions in males and females. The present study is one of the first to use pleopod morphometry to determine sexual maturity and dimorphism in hermit crabs, especially for species with intersexuality such as I. sawayai.