On the taxonomy and biogeography of Potamon atkinsonianum (Wood-Mason, 1871) and Potamon (Potamon) emphysetum (Alcock, 1909)

The Himalayas are known to be a geologically young and dynamic mountain range hosting an endemic flora and fauna. To date, for freshwater crabs, one endemic subgenus within the genus Potamon, Potamon (Himalayapotamon) Pretzmann, 1966, has been described from the Himalayas. This subgenus includes two species, Potamon atkinsonianum (Wood-Mason, 1871) and Potamon emphysetum (Alcock, 1909). The taxonomic position of these two species is reconsidered. The subgenus Himalayapotamon is raised to generic level and its systematic and zoogeographic position is discussed. Based mainly on the morphology of the male copulatory system, Himalayapotamon belongs to the family Potamidae. It is more related to the Eurasian genus Potamon Savigny, and is distinct from the South-East Asian genus Potamiscus as well as from the Indian freshwater crabs of the family Gecarcinucidae. Zoogeographically Himalayapotamon appears to be an endemic genus related to Potamon, both genera presumably being isolated during the Miocene when the Gangetic waters were separated from the western Eurasian river systems. Further speciation occurred during glacial periods.     

Ultrastructure and relationships of spermatozoa of the freshwater crabs Potamon fluviatile and Potamon ibericum (Crustacea, Brachyura, Potamidae)

The spermatozoa of Potamon fluviatile and P. ibericum are virtually indistinguishable and do not support separate subgeneric rank ( Potamon and Pontipotamon , respectively). Synapomorphic with the spermatozoa of the South African freshwater crab Potamonautes perlatus Sidneyi are the elongation of the two centrioles and disposition of the centrioles almost parallel to each other, unknown elsewhere in the Brachyura, and reduction of the thickened ring (homoplasic with grapsids and gecarcinids). Other, probably synapomorphic, similarities of Potamon and Potamonautes include the wide inner acrosome zone, absence of a definite acrosome ray zone (homoplasic in other families) and the cleistospermial spermatophores. Further similarities, of questionable polarity, are the simple, not multilaminar, nuclear membrane and the tendency of the nuclear arms to wrap around the nucleus. Differences of Potamon from Potamonautes , which possibly support their present generic separation and give weak support to their former separate familial placement in the Potamidae and Potamonautidae respectively, are perforation of the operculum and the weak, rather than strong, development of a periopercular rim. Absence in Potamon and Potamonautes of an accessory opercular ring and a xanthid ring separates them from xanthids. No close affinities with other heterotreme families are seen but their assignment to the Helerotremata is not in doubt. Their spermatozoa lack two of the distinctive features of thoracotreme spermatozoa (apical button on the operculum and concentric lamellation of the outer acrosome zone). No clear correlates of spermatozoon structure with a freshwater existence are recognizable but reduction of the thickened ring possibly relates to peculiarities of the acrosome reaction. However, the production of spermatophores with single spermatozoa (cleistospermia) is possibly a device to prevent polyspermy and wastage of the small number of lecithotrophic eggs produced in potamids.     

Revalidation and redescription of Potamon elbursi Pretzmann, 1976 (Brachyura, Potamidae) from Iran, based on morphology and genetics

In the current study, we redescribe and revalidate a freshwater crab species of the genus Potamon Savigny, 1816, from northern Iran. Potamon elbursi Pretzmann, 1962, differs from the species it has been synonymised with, Potamon persicum Pretzmann, 1962, mainly by the shape of the first gonopods in males. Consistent and marked genetic divergence was also recognised in the mitochondrial 16S rRNA and cytochrome oxidase subunit I genes. This study elevates P. elbursi to species rank and therefore increases the number of valid species of the genus Potamon to a total of twenty-two.     

The morphology of the gills of the freshwater African crab Potamon niloticus (Crustacea: Brachyura: Potamonidae): A scanning and transmission electron microscopic study

The gills of the African freshwater crab Potamon niloticus -Ortmann have been investigated by scanning and transmission electron microscopy. Potamon has seven pairs of phyllobranchiate gills contained in the branchial chambers. From the central axis of the gills arise bilaterally situated thin flaps, the lamellae. The afferent branchial vessel (the epibranchial vessel) is located on the dorsal aspect of the gill arch and the efferent vessel (the hypobrancial vessel) on the ventral side. Between these two blood vessels, the blood percolates through the lamellar vascular channels where it is oxygenated. The lamellae consist of an epithelial cell layer covered by a thin cuticle which consists of tightly fused but distinct layers. The epithelial cells approach each other at regular intervals and fuse in the middle of the lamellar sinus delineating the vascular channels. Apical profuse membranous infoldings and numerous mitochondria characterize the epithelial cells, features typical of cells involved in active transport of macro- and micromolecules. In Potamon , however, there were no distinct gas exchange and osmoregulatory regions of the gills. On average, the cuticle was 0.78 μm thick while the epithelial cell was 6 μm. Cells that were morphologically similar to the renal glomerular podocytes of the vertebrates were observed in the efferent gill vessel of Potamon. These cells have been said to be phagocytic and may play an important defensive role in the crustaceans. Although basically the morphology of the gills of Potamon is similar to that of the other decapods, fine structural differences were evident as would be intuitively expected in a group of animals that has undergone such remarkable adaptive radiation.     

A revision of the freshwater crab genus Hainanpotamon (Crustacea: Decapoda: Brachyura: Potamidae: Potamiscinae), with a redescription of Potamon (Potamon) orientale (Parisi, 1916) and descriptions of three new species

The taxonomy of the potamid genus Hainanpotamon , from Vietnam, Laos, Hainan Island (China) and, purportedly, Okinawa Island (Japan) is reviewed. The type species, Potamon (Potamon) orientale (), is redescribed and a lectotype designated. In addition, three new species are described. The poorly known species Potamon (Geothelphusa) globosum , is assigned to Hainanpotamon and its taxonomy clarified, with a lectotype designated. A key to the nine species of Hainanpotamon is provided.     

Evolution of freshwater crab diversity in the Aegean region (Crustacea: Brachyura: Potamidae)

The aim of this study was to estimate the influence of the palaeogeographic and climatic history of the Aegean region on the diversity of freshwater crabs of the genus Potamon and to test whether this area served as source or reservoir in species diversity. Necessary species delimitation was accomplished by phylogenetic analyses of the mitochondrial markers COX1 and ND1, partial 16S rRNA gene and the tRNALeu gene. We found 14 genetic lineages of which nine could be assigned to previously recognised species. Temporal estimates of the splitting pattern in the phylogeny of Potamon indicated that a combination of geological and climatic events influenced their diversification. Within Potamon, the lineages separated into a western group and an eastern group. This first split in the genus occurred approximately 8.3-5.5 Mya, thus possibly correlated with the Messinian salinity crisis. A likelihood approach to geographic range evolution suggested for most species, occurring in the Aegean area, an origin in the Middle East. Moreover, there were no insular endemics in the central Aegean archipelago, therefore low sea-levels during the Pleistocene glacial periods possibly enabled dispersal to these islands, but subsequent rise in sea-level did not cause speciation. Nevertheless, the diversification of most lineages occurred during the Pleistocene epoch thus coinciding with Quaternary fluctuations of the climate.     

Mating behavior,egg laying,and embryonic development in the South American apple snail Asolene pulchella (Ampullariidae,Caenogastropoda)

Asolene pulchella is a dioecious freshwater snail from the La Plata basin, belonging to the Ampullariidae family. Our aim was to study the reproductive biology, including mating behavior, egg laying, and embryonic development under laboratory conditions. Copulations occurred underwater and lasted 2.66?h on average. The males produce fusiform paraspermatic cells (with seven to nine flagella) in addition to euspermatic cells with a corkscrew head, straight middle piece and long flagellum. Females stored sperm for up to 169?days. The egg masses (containing 98.1 eggs on average) are deposited underwater and are composed of many gelatinous packs of 1–4 eggs; the jelly matrix presented numerous calcite microcrystals. The spheroidal egg capsules measured 2.25?mm and contained a yellowish perivitellus of rubbery consistence. The embryonic development extends for 10.8?days on average. Hatchlings measured 1.4?mm and remained on the egg mass, feeding on the jelly. They resemble miniature adults but only began to feed on senescent plant material in their third week of age and begin aerial lung respiration after 8–10?weeks. The details of the structure of the egg masses and development constitute a rich source of traits for comparative and taxonomic studies in the Ampullariidae.     

Kleptoparasitism of freshwater crabs by cichlid fishes endemic to Lake Barombi Mbo,Cameroon, West Africa

Synopsis Although kleptoparasitism, or food-stealing, is common in birds and some carnivorous mammals, reported instances are exceedingly rare in fishes. We studied the behaviour and ecology of the 11 endemic tilapiine cichlids of Lake Barombi Mbo, Cameroon, West Africa. Here we report that six of the Barombi cichlids (Stomatepia mariae, S. pindu, Konia eisentrauti, Pungu maclareni, Sarotherodon lohbergeri, andS. linnellii) kleptoparasitize freshwater crabsPotamon africanus.     

Variability In the rate of egg development of the stonefly, Nemoura cinerea (Plecoptera)

SUMMARY. 1. The egg development of the widely distributed European stonefly. Nemoura cinerea Retzius. was investigated in the laboratory. There was a significant relationship between water temperature (T°C) and incubation period (Ydays), expressed by the regression equation: Y = 239 T^−0.85 (r²= 0.85. P<0.001).
2. The number of day-degrees above 0°C required for hatching showed a curvilinear relationship with water temperature, with a minimum requirement around 12°C.
3. Nemoura cinerea shows more variation in the rate of egg development than most other stoneflies. This, in part, explains the wide size range in nymphal populations and the species' extended emergence period. Flexibility in life cycle and asynchrony in egg development enable this species to colonize a wide range of freshwater habitats.     

Movement patterns of river crabs (Decapoda, Potamoidea) in the field: predictable and unpredicatable components

Radio-telemetry was used to investigate locomotor activity rhythms in a field population of the freshwater crab Potamon fluviatile . Fourteen adult specimens were radio-tracked almost continuously over a 13-day period along a hill stream in Tuscany, Italy. A rough nychthemeral movement pattern was found in some animals of both sexes. None of the crabs showed a constant activity on different days, nor did they follow any periodical pattern. Although average displacement amounted to about 5m/d, activity was concentrated over several days at a time, followed randomly by periods of almost total inactivity. On average, only about 3/4 of radio-tagged crabs were active every day and only a small fraction active at the same time. The crabs spent about 60% (females) or 70% (males) of their time out of the water, but there was no regular pattern in land-water preference. The random high variation in locomotor activity on different days seems to be a constant pattern in all decapods that have been studied so far, using individual marking techniques.     

Patterns in stage duration and development among marine and freshwater calanoid and cyclopoid copepods: a review of rules,physiological constraints,and evolutionary significance

Studies of development time of marine and freshwater copepods have taken separate tracks. Most studies on marine copepods report development time of each individual development stage, whereas studies on freshwater copepods report only development time, from egg to nauplius and nauplius to adult. This bias allows comparison of total development time but prevents detailed comparisons of patterns in stage-specific developmental schedules. With respect to egg to adult development time, three general relationships are known: developmental rates are dependent upon temperature and food concentration but independent of terminal body size; freshwater calanoids develop significantly slower than marine calanoids; freshwater cyclopoids develop at the same rate as marine calanoids. Two rules describe stage-specific developmental rates: the equiproportional rule and the isochronal rule. The first rule states that the duration of a given life history stage is a constant proportion of the embryonic development time; the second rule states that the time spent in each stage is the same for all stages. This review focuses on the second rule. From the 80+ published studies of copepod stage-specific developmental times, no species follows the isochronal rule strictly: Acartia spp. come closest with isochronal development from third nauplius (N3) to fourth copepodite (C4). The only pattern followed by all species is rapid development of the first and/or second naupliar stages, slow development of the second and/or third nauplius and prolonged development of the final copepodite stage. Once adulthood is reached, males are usually short-lived, but females can live for weeks to months in the laboratory. Adult longevity in the sea is, however, on the order of only a few days. The evolution of developmental patterns is discussed in the context of physiological constraints, along with consideration of possible relationships between stage-specific mortality rates and life history strategies. Physiological constraints may operate at critical bottlenecks in development (e.g. at the first feeding nauplius, N6, and the fifth copepodite stage). High mortality of eggs may explain why broadcast eggs hatch 2–3 times faster than eggs carried by females in a sac; high mortality of adults may explain why adults do not grow rather they maximize their reproductive effort by partitioning all energy for growth into egg production.     

Partial purification and properties of (Na+ + K+)-ATPase from Potamon potamios.

1. The tissue distribution of the (Na+ + K+)-ATPase in the freshwater/land crab Potamon Potamios was studied. 2. Gills were found to display the highest total activity in the whole animal (47%) but the highest specific activity was detected in the heart (15.15 mumol Pi/mg protein/min). 3. All other organs tested were found to have low enzyme activity. 4. The freshwater/land crab ATPase enzyme was inhibited by ouabain with a Ki of 0.5 mM.Km values for ATP, Mg2+ and K+ were 1.4, 4.0 and 1.2 mM respectively. The enzyme also showed a break in the Arrhenius plot at 23 degrees C. 5. A purification method of microsomal ATPase is described involving ultracentrifugation and electrofocusing.     

Effect of salinity on the embryonic development of Macrobrachium acanthurus (Decapoda: Palaemonidae)

The effect of salinity level on the embryonic development of Macrobrachium acanthurus was analyzed under laboratory conditions, considering characteristics of the egg (size, volume, and water content) and of the embryo (eye index). The experimental design was completely randomized, with five repetitions (ovigerous females) per treatment (0, 10, 17 and 20 ppt). During embryonic development, two eggs per female were taken daily for analyses of size, volume, water content, and eye index. Our results showed that salinity of 20 ppt leads to death and/or abortion of the embryo in all females. The size, volume and water content of eggs increased according to embryonic development, providing space in the egg for formation and organization of embryo. Salinity affected these egg characteristics, causing water loss to the hypertonic medium. Neither the duration of embryonic development nor embryo formation were affected by saltwater content. The results of the present study indicate that ovigerous females of M. acanthurus can survive in freshwater rivers as well as in low-salinity environments during incubation period and the successful larval development is not likely to rely on female migrating to estuaries. Larvae can easily be incubated in freshwater and complete development at higher salinities after hatch.     

Studies on the life-cycle of Pleurogenoides ovatus Rao, 1977 (Trematoda: Pleurogenetinae)

The life-cycle of Pleurogenoides ovatus Rao, 1977, infecting the frogs, Rana tigrina and R. cyanophlyctis has been elucidated. All the life-cycle stages from egg to egg-producing adults were successfully established in the laboratory. The life-cycle took about 80 days for completion. Cercariae were found in the freshwater snail. Digoniostoma pulchella, collected from paddy fields at Chelembra, Malappuram district of Kerala, during the monsoon months. Cercariae are of the virgulate xiphidiocercous type. Metacercariae occurred in the connective tissues, hepatopancreas and musculature of the freshwater crab, Paratelphusa hydrodromous. The growth and development of the metacercariae in P. hydrodromous have been studied in detail. Frogs became infected when they fed on infected crabs. The prepatent period is 10 days.     

Differentiation of the vitelline coat and the polarized site of sperm entrance in the egg of Unio elongatulus (Mollusca, Bivalvia)

We studied the differentiation of the polarized site of sperm entrance in the egg of a freshwater bivalve, Unio elongatulus. As previously shown, in this egg model the property of sperm recognition and binding is restricted to a region characterized by a wrinkled surface which surrounds a truncated cone or crater region, at the vegetal pole of the egg. The crater is formed during oogenesis at a site opposite the oocyte attachment to the ovarian wall. It first appears as a small bleb, and later detaches, leaving in the oocyte an open narrow process filled with an orderly array of microtubules. Here the vitelline coat differentiates from the rest of the oocyte. The role of the microtubules in the formation of the region and the differential distribution of the vitelline coat components is discussed. The synthesis during development of fucosyl containing glycoproteins and their presence in an electrophoretic pattern of isolated vitelline coats were also studied using Lotus tetragonolobus (LTA) conjugated with fluorescein and peroxidase.     

The interrelation of the size of fish eggs, the date of spawning and the production cycle

The variability in size of pelagic and demersal marine and freshwater fish eggs is examined. The difference between the smallest and largest volumes, based on published figures for the diameters, is large in many species. In marine species with planktonic eggs, the median percentage difference is just over 100%, and this is similar in species with demersal eggs and in freshwater fish.
The available evidence suggests that geographical differences in egg size are small, but in marine fish there is a well-known seasonal decline in egg size. In herring it has previously been shown that egg size in different spawning groups can be correlated with the timing of the production cycle. A similar correlation can be seen in the seasonal shift in time and locality of spawning, and egg size, of the plaice. Sufficient data on seasonal freshwater fish egg variations are not available, but the time of spawning does appear to be linked with the availability of food for the larvae in both lake and stream species.     

Partial purification and properties of (Na+ + K+)-ATPase from Potamon potamios

1. The tissue distribution of the (Na⁺ + K⁺)-ATPase in the freshwater/land crab Potamon Potamios was studied.2. Gills were found to display the highest total activity in the whole animal (47%) but the highest specific activity was detected in the heart (15.15 μmol Pi/mg protein/min.).3. All other organs tested were found to have low enzyme activity.4. The freshwater/land crab ATPase enzyme was inhibited by ouabain with a Ki of 0.5 mM.Km values for ATP, Mg²⁺ and K⁺ were 1.4, 4.0 and 1.2mM respectively. The enzyme also showed a break in the Arrhenius plot at 23°C.5. A purification method of microsomal ATPase is described involving ultracentrifugation and electrofocusing.     

Organic,inorganic, and caloric composition of eggs,pentaculae, and adults of the brooding sea cucumber Cucumaria curata cowles (Echinodermata: Holothuroidea)

Levels (percentage composition) of water, ash, carbohydrate, lipid, protein, and calories were determined for eggs, pentaculae, and adults of the sea cucumber Cucumaria curata Cowles. Component contents (μg/individual) were calculated for eggs and pentaculae. During the 28 days of development to hatching, the large yolky eggs gain water and ash, the total dry weight increasing from 169 to 190 μg/egg during embryogenesis. There were no statistically significant changes in lipid, protein, and caloric contents during embryogenesis, but carbohydrate decreased by 0.82 μg/egg.The decrease in carbohydrate is sufficient to account for estimated embryonic energy requirements. Based on the utilization of carbohydrate, embryos of C. curata show a nutritional pattern similar to that of the planktonic embryos of sea urchins and different from that of embryos developing from terrestrial eggs, freshwater eggs, and planktonic and demersal marine eggs.Although broods varied widely in egg number and mean egg dry weight, C. curata gives eggs which contain a constant proportion of organic components.Levels of ash, water, and protein in the adults exceeded those in the pentacula, and lipid comprises a much smaller proportion of the adult body than it did of the pentacula.     

Egg development, nymphal growth and life cycle strategies in Plecoptera

Interspecific and intraspecific differences in egg development, nymphal growth and the life cycles of Fennoscandian stoneflies are examined in relation to zoogeographical aspects and evolutionary trends. Data on other European and North American species are also considered.
Egg development shows considerable diversity, the main categories being ovovivipary, egg development with diapause and non-diapause development. Egg development in species in the non-diapause category can be classified as eurythermal, cold stenothermal or warm stenothermal. Temperature has a marked effect on nymphal growth of some species but not others. The distribution of several species can be explained by their temperature relationships, either in the egg or nymphal stage. Several species modify their life cycle to fit local climatic conditions. In some species, such as Leuctra hippopus , environmental selection has been so strong that they have probably recently evolved into subspecies and/or species in northern Europe.
Morphological and ecological variations in the Plecoptera have facilitated their colonization of the variety of freshwater biotopes that occur in Fennoscandia.     

Comparative size,biomass, elemental composition (C,N, H), and energy concentration of caridean shrimp eggs

Summary

In the evolution of decapod crustaceans, interspecific variation in egg size is considered as an important life-history trait that is linked with the duration of embryonic and larval development, the number and type of larval stages, and with juvenile size. Aiming to provide a quantitative characterization of reproductive traits in related decapod taxa differing in lifestyle (freshwater, estuarine, marine) and geographic-climatic distribution (tropical-temperate), we compared size, biomass, and elemental composition of eggs of caridean shrimps from three families: seven species of Palaemonidae (three congeners of Macrobrachium: M. olfersii, M. carcinus, M. acanthurus; four species of Palaemon: P. northropi, P. pandaliformis, P. elegans, P. adspersus), two Atyidae (Potimirim potimirim, Atya scabra), and one Pandalid (Pandalus montagui). Egg size was measured as larger and smaller diameter (D₁ D₂), volume was calculated from D₁ and D₂, and biomass was measured as dry mass (W), carbon (C), nitrogen (N), hydrogen (H), and energy (E, estimated from C) contents. The smallest size and lowest biomass were found in the eggs of two freshwater atyids (both originating from Brazil); the largest size occurred in a marine species, P. montagui (from the North Sea); and intermediate values in freshwater, estuarine, and marine palaemonid species (from Brazil and the Baltic Sea, respectively). Among the Palaemon species, the most limnic (P. pandaliformis) showed a significantly larger egg size and volume (P<0.001) than the estuarine and marine congeners, P. elegans, P. adspersus and P. northropi. This suggests that the generally postulated relationship between egg size and lifestyle (freshwater vs. estuarine or marine) may appear at a generic but not at the family level. On the other hand, individual biomass (in μg or Joules per egg) of early eggs was significantly higher in P. elegans and P. adspersus, indicating interspecific variability in biomass and energy concentration (in μg or Joules per unit volume, mm³). Generally lower biomass concentrations in early eggs of freshwater shrimps may be caused by a higher average water content. Eggs in late embryonic stages were generally larger than earlier eggs of the same species, reflecting an increase in the water content, while an increasing D₁:D₂ quotient indicated an increasingly elongated egg shape. The biomass per egg decreased during embryonic development due to metabolic degradation of organic reserves. As a consequence of inverse ontogenetic changes in size and organic biomass of developing eggs, the mass-specific biomass values (C, N, H in percent of W; E in Joules per mg W) and volume-specific concentrations (μg or Joules per unit volume) decreased. This change was consistently stronger in the C, H, and E contents than in other measures of biomass (W, N). In consequence, the C:N mass ratio also decreased, suggesting that lipid degradation rather than protein utilization was the principal fuel for embryonic development. Our results indicate high intra- (mainly developmental) and interspecific variation in reproductive traits of closely related species. While volume-specific biomass and energy concentrations of early eggs appear to be associated with variation in habitat salinity (freshwater, brackish, marine), individual egg size and biomass may be related more with the climatic-geographic distribution (temperate, tropical) of different taxa.