Bioenergetics of abbreviated larval development in the bromeliad crab,Metopaulias depressus (Decapoda: Grapsidae)

• 1.1. Larvae of the bromeliad crab, Metopaulias depressus Rathbun, were reared in the laboratory, and changes in dry weight (W), ash-free W (AFW), carbon, nitrogen, hydrogen, protein, lipid, carbohydrates and respiration rate were measured during development from hatching to metamorphosis.
• 2.2. Development was successful in rain-water from bromeliads (pH < 5–6), but not in river water from the same region (pH 8). It is abbreviated, with two non-feeding zoeal stages (2.5–3.5 days each) and a feeding megalopa (8.5–10 days). Development to metamorphosis can also be completed in the absence of food (facultative lecithotrophy).
• 3.3. Dry weight and other absolute biomass values per individual vary significantly between different hatches, whereas changes in the relative (% of W or AFW) composition follow quite invariable patterns: ash increases from hatching through the first part of megalopa development, organic biomass decreases concurrently.
• 4.4. Elemental and biochemical data show that lecithotrophy of the zoeal stages as well as continued endotrophic development in the megalopa depend chiefly on degradation of lipid reserves and less on protein. No significant growth was observed in organic constituents when food was available, but without food the megalopa reached metamorphosis with only half the lipid and less than two thirds the protein of fed siblings.
• 5.5. The relationship between C and lipid is similar in M. depressus larvae as in planktotrophic marine crab larvae, whereas that between N and protein differs; it indicates the presence of unusually large quantities of unidentified non-protein N.
• 6.6. Exuvial losses of late premoult biomass or energy are very low in the zoeal stages (2 and 3%), but increase in the megalopa (16% in W, 10% in C, 7–8% in N, H and energy).
• 7.7. Respiration rate per individual increases gradually during larval development (0.6–0.8 μg O₂/hr). Starved megalopa larvae reveal lower individual but higher W-specific metabolism than fed larvae.
• 8.8. Bioenergetic traits of abbreviated larval development are discussed in relation to those known from regular (planktotrophic marine) development of brachyuran crabs. M. depressus is highly adapted to life and development in a physically extreme terrestrial environment.

     

Adaptive diversity in congeneric coastal crabs: Ontogenetic patterns of osmoregulation match life-history strategies in Armases spp (Decapoda, Sesarmidae)

Ontogeny of osmoregulation and salinity tolerance were investigated throughout the larval development of two congeneric species of sesarmid crab, Armases ricordi (H. Milne Edwards) and A. roberti (H. Milne Edwards), and compared with previous observations from two further congeners, A. miersii (Rathbun) and A. angustipes (Dana). In the semiterrestrial coastal species A. ricordi, the zoeal stages were only at moderately reduced salinities (17-25.5‰) capable of hyper-osmoregulation, being osmoconformers at higher concentrations. The megalopa was the first ontogenetic stage of this species, which exhibited significant hyper-osmoregulation at further reduced salinities (≥ 5‰), as well as a moderately developed function of hypo-regulation at high concentrations (32-44‰). The riverine species A. roberti showed similar overall patterns in the ontogeny of osmoregulation, however, also some striking differences. In particular, its first zoeal stage showed already at hatching a strong capability of hyper-osmoregulation in salinities down to 5‰. Interestingly, this early expressed function became significantly weaker in the subsequent zoeal stages, where survival and capabilities of hyper-osmoregulation were observed only at salinities down to 10‰. The function of hyper-regulation in strongly dilute media re-appeared later, in the megalopa stage, which tolerated even an exposure to freshwater (0.2‰). Differential species- and stage-specific patterns of osmoregulation were compared with contrasting life styles, reproductive behaviours, and life-history strategies. In A. ricordi, the larvae are released into coastal marine waters, where salinities are high, and thus, no strong hyper-osmoregulation is needed throughout the zoeal phase. The megalopa stage of this species, by contrast, may invade brackish mangrove habitats, where osmoregulatory capabilities are required. Strong hyper-osmoregulation occurring in both the initial and final larval stages (but not in the intermediate zoeal stages) of A. roberti correspond to patterns of ontogenetic migration in this species, including hatching in freshwater, larval downstream transport, later zoeal development in estuarine waters, and final re-immigration of megalopae and juvenile crabs into limnic habitats, where the conspecific adults live. Similar developmental changes in the ecology and physiology of early life-history stages seem to occur also in A. angustipes. A. miersii differs from all other species, showing an early expression and a gradual subsequent increase of the function of hyper-osmoregulation. This ontogenetic pattern corresponds with an unusual reproductive biology of this species, which breeds in supratidal (i.e. land-locked) rock pools, where variations in salinity are high and unpredictable. Matching patterns in the ontogeny of osmoregulation and life-history strategies indicate a crucial adaptive role of osmoregulation for invasions of (by origin marine) crabs into brackish, limnic and terrestrial environments.     

Developmental patterns of larval growth in the edible spider crab, Maja brachydactyla (Decapoda: Majidae)

The large edible spider crab Maja brachydactyla Balss, 1922, an overexploited coastal fishery resource in Galicia (NW Spain), is considered as a potential aquaculture candidate. Patterns of its larval growth were studied under controlled laboratory conditions (constant 18 ± 1 °C; 36‰ salinity; photoperiod ca. 12:12 h; lipid-enriched Artemia metanauplii provided as food). From hatching through complete larval development and metamorphosis to the first juvenile crab instar, changes in carapace size, dry weight (DW), ash content, elemental composition (carbon, hydrogen, nitrogen; CHN), and proximate biochemical composition (total proteins, lipids, carbohydrates; Pr, L, Ch) were measured in successive stages (zoea I, II, megalopa, crab I). Body size may be described as a linear function of the number of molting cycles, whereas the amounts of DW, CHN, Pr, L, and Ch per individual increased exponentially (3 to 9 fold). The highest growth rates were observed in L, C and H, the lowest in DW, Pr and N. As a consequence of these patterns, the C:N mass ratio as well as the fractions of L, C and H (in % of DW) increased significantly, while those of Pr and N decreased from 26% to 16% of DW. Throughout development, however, Pr remained the principal biochemical component of total DW. Positive correlations between biochemical and CHN data allow for estimates of Pr from N and of L from C values per individual. The patterns of larval growth observed in M. brachydactyla are, in general, similar to those previously described for other brachyuran crabs with a planktotrophic mode of larval development.     

Larval development of the subantarctic king crabs<Emphasis Type="Italic"> Lithodes santolla</Emphasis> and<Emphasis Type="Italic"> Paralomis granulosa</Emphasis> reared in the laboratory

The larval development and survival in the two subantarctic lithodid crabs Lithodes santolla (Jaquinot) and Paralomis granulosa (Molina) from the Argentine Beagle Channel were studied in laboratory cultures. In L. santolla, larval development lasted about 70 days, passing through three zoeal stages and the megalopa stage, with a duration of approximately 4, 7, 11 and 48 days, respectively. The larval development in P. granulosa is more abbreviated, comprising only two zoeal stages and the megalopa stage, with 6, 11 and 43 days' duration, respectively. In both species, we tested for effects of presence versus absence of food (Artemia nauplii) on larval development duration and survival rate. In P. granulosa, we also studied effects of different rearing conditions, such as individual versus mass cultures, as well as aerated versus unaerated cultures. No differences in larval development duration and survival were observed between animals subjected to those different rearing conditions. The lack of response to the presence or absence of potential food confirms, in both species, a complete lecithotrophic mode of larval development. Since lithodid crabs are of high economic importance in the artisanal fishery in the southernmost parts of South America, the knowledge of optimal rearing conditions for lithodid larvae is essential for future attempts at repopulating the collapsing natural stocks off Tierra del Fuego.Communicated by H.-D. Franke     

Studies on the larval development of northeastern Atlantic and Mediterranean Procellanidae (Decapoda,Anomura). I — Redescription of the larval stages ofPorcellana platycheles (Pennant, 1777) reared under laboratory conditions

The complete larval development is described forPorcellana platycheles (Pennant) reared under laboratory conditions. The development consists of two zoeal stages and one megalopa. At 20°C and 35‰ salinity, the megalopa appeared 17–18 days after hatching. Survival was 56% from hatching to the megalopa stage. The morphological features of the zoeal and megalopa stages ofP. platycheles are compared with those of other species ofPorcellana, and a key of the known zoeal stages of the genus is given.     

Changes in biomass and chemical composition during lecithotrophic larval development of the southern king crab, Lithodes santolla (Molina)

Changes in biomass and elemental composition (dry mass, W; carbon, C; nitrogen, N; hydrogen, H) were studied in the laboratory during complete larval and early juvenile development of the southern king crab, Lithodes santolla (Molina), formerly known as Lithodes antarcticus (Jacquinot). At 6±0.5 °C, total larval development from hatching to metamorphosis lasted about 10 weeks, comprising three demersal zoeal stages and a benthic megalopa, with mean stage durations of 4, 7, 11 and 47 days, respectively. No differences in development duration or mortality were observed in larvae either fed with Artemia sp. nauplii or unfed, indicating that all larval stages of L. santolla are lecithotrophic. First feeding and growth were consistently observed immediately after metamorphosis to the first juvenile crab stage. Regardless of the presence or absence of food, W, C, N and H decreased throughout larval development. Also the C:N mass ratio decreased significantly, from 7.7 at hatching to 4.1 at metamorphosis, indicating that a large initial lipid store remaining from the egg yolk was gradually utilized as an internal energy source, while proteins played a minor role as a metabolic substrate. In total, 56-58% of the initial quantities of C and H present at hatching, and 20% of N were lost during nonfeeding larval development to metamorphosis. Nine to ten percent of the initially present C, N and H were lost with larval exuviae, half of these losses occurring in the three zoeal stages combined and another half in the megalopa stage alone. Metabolic biomass degradation accounted for losses of about 47-50% in C and H but for only 10% in N. Hence, most of the losses in C and H reflected metabolic energy consumption (primarily lipid degradation), while about half of the losses in N and two thirds of those in W were due to larval exuviation. Complete independence from food throughout larval development is based on an enhanced maternal energy investment per offspring and on energy-saving mechanisms such as low larval locomotory activity and low exuvial losses. These traits are interpreted as bioenergetic adaptations to food-limited conditions in Subantarctic regions, where a pronounced seasonality of day length limits the period of primary production, while low temperatures enforce a long duration of pelagic development.     

Larval and early juvenile development of Lithodes santolla (Molina, 1782) (Decapoda: Anomura: Lithodidae) reared at different temperatures in the laboratory

The southern king crab, Lithodes santolla Molina, is distributed in cold-temperate and subantarctic waters ranging from the southeastern Pacific island of Chiloé (Chile) and the deep Atlantic waters off Uruguay, south to the Beagle Channel (Tierra del Fuego, Argentina/Chile). Recent investigations have shown that its complete larval development from hatching to metamorphosis, comprising three zoeal stages and a megalopa, is fully lecithotrophic, i.e. independent of food. In the present study, larvae were individually reared in the laboratory at seven constant temperatures ranging from 1 to 18 °C, and rates of survival and development through successive larval and early juvenile stages were monitored throughout a period of 1 year. The highest temperature (18 °C) caused complete mortality within 1 week; only a single individual moulted under this condition, 2 days after hatching, to the second zoeal stage, while all other larvae died later in the zoea I stage. At the coldest condition (1 °C), 71% of the larvae reached the zoea III stage, but none of these moulted successfully to a megalopa. A temperature of 3 °C allowed for some survival to the megalopa stage (17-33% in larvae obtained from two different females), but only a single individual passed successfully, 129 days after hatching, through metamorphosis to the first juvenile crab instar. At all other experimental conditions (6, 9, 12 and 15 °C), survival through metamorphosis varied among temperatures and two hatches from 29% to 90% without showing a consistent trend. The time of nonfeeding development from hatching to metamorphosis lasted, on average, from 19 days at 15 °C to 65 days at 6 °C. The relationship between the time of development through individual larval or juvenile stages (D) and temperature (T) was described as a power function (D=aT^b, or log[D]=log[a]blog[T]). The same model was also used to describe the temperature dependence of cumulative periods of development from hatching to later larval or juvenile stages. One year after hatching, the 7th (6 °C) to 9th (15 °C) crab instar was reached. Under natural temperature conditions in the region of origin of our material (Beagle Channel, Argentina), L. santolla should reach metamorphosis in October-December, i.e. ca. 2 months after hatching (taking place in winter and early spring). Within 1 year from hatching, the crabs should grow approximately to juvenile instars VII-VIII. Our results indicate that the early life-history stages of L. santolla tolerate moderate cold stress as well as planktonic food-limitation in winter, implying that this species is well adapted to subantarctic environments with low temperatures and a short seasonal plankton production.     

Partitioning and utilization of energy during the larval development of the xanthid crab, Rhithropanopeus harrisii (Gould)

An energy budget is constructed for the larval development of the crab Rhithropanopeus harrisii (Gould) fed nauplii of the brine shrimp Artemia salina (L.). Between the first zoeal instar and the megalopa, there is a 5.4-fold increase in caloric consumption and a 13.2-fold increase in dry weight. Weight specific energy content increases through the zoeal stages and drops at the megalopa. Rate of oxygen consumption increases steadily throughout development. Assimilation, gross growth, and net growth efficiencies increase steadily through zoeal development and drop at the megalopa. Calories put into tissue production exceed those expended via respiration in zoeal stages II–IV; the reverse is true in zoeal stage I and the megalopa.

A total energy budget has been calculated and the partitioning of energy is discussed in relation to other physiological studies on this species.     

Larval development of the subantarctic squat lobster Munida subrugosa (White, 1847) (Anomura: Galatheidae), reared in the laboratory

The larval development of the squat lobster Munida subrugosa from subantarctic waters of the Beagle Channel (Tierra del Fuego, Argentina) was studied under controlled laboratory conditions of temperature, salinity, and food supply. Developmental times, survival, and growth of larvae and early juveniles were investigated. Hatching of the entire brood always occurred during one night. Larvae were kept in 100ml individual bowls with filtered seawater at 8 ± 0.5°C and fed with Artemia spp. nauplii three times a week. Larvae passed through 6 zoeal instars and one megalopa. Previously, only five zoeal instars were known from this species. Mean cumulative durations of the zoeal stages I to VI were: 20.5 ± 2.5, 33.9 ± 4.1, 43.3 ± 5.4, 52.6 ± 5, 61.2 ± 3.9, and 83days, respectively. By adding the 28days that a single megalopa took to metamorphose to crab I stage, the complete larval development lasted 111days. Highest mortality occurred prior to the moult from the zoea I to zoea II stage (79.21% ± 18.65%) and during the moult from zoea VI to megalopa (92.86%). Carapace length was 1.64 ± 0.06, 1.52 ± 0.16, 1.57 ± 0.26, 1.64 ± 0.21, 2.11 ± 0.35, and 2.58 ± 0.19mm, for zoeal stages I to VI, respectively. Carapace length of megalopae and crab I instars was similar (2.85 ± 0.28 and the 2.84 ± 0.05, respectively). Unlike other subantarctic decapods, which show a tendency towards abbreviated larval development and/or some degree of endotrophy, M. subrugosa shows an extended planktotrophic larval development synchronized with short seasonal plankton production in austral summers.     

Comparative morphology of larvae of coastal crabs (Crustacea: Decapoda: Varunidae)

The larval development of three crabs of the Varunidae family, (Hemigrapsus sanguineus, H. penicillatus, and H. longitarsis), widely spread in Russian waters of the Sea of Japan, were studied under laboratory conditions. At a temperature of 20–22°C and a salinity of 32‰ about 30% of larvae a complete developmental cycle, including five zoeal stages and megalopa, took from 22 to 30 days. All larval stages are illustrated and described in detail. Zoea I and zoea II of the studied crabs are not distinguishable. Zoea III–V of these species differ in the number of dorsomedial setae on the abdominal somite I and in the number of setae on the posterodorsal arch. The megalopae of three Hemigrapsus species possess a different number of segments, aesthetascs and setae on the antennular exopod. In spite of the great similarity of larvae of genera Hemigrapsus and Eriocheir, the latter possesses a number of distinctive features in all developmental stages, supporting the separation of these genera.     

Occurrence of additional Zoea-VI larvae in the mud crab, Scylla paramamosain (Estampador), reared in the laboratory

Mud crabs, Scylla spp. , are commercially important in many Indo-Pacific countries. The larval development of mud crabs has been reported previously as five zoeal and one megalopal stages. This paper reports larval rearing experiments that revealed variability in larval developmental stages in the mud crab Scylla paramamosain, one of four mud crab species. In addition to normal five zoeal stages, an alternative pathway of developing through six zoeal stages was observed for the crab. There were evidences suggested that the appearance of the additional Zoea-VI larvae was associated with unfavourable dietary conditions, including poor quality of diet, inadequate quantity of dietary supply and a period of starvation for newly hatched larvae. Based on exuviae and larval specimens, the morphology of the additional Zoea-VI larvae was described.     

Larval development ofNeopisosoma neglectum werding, 1986 (Decapoda: Anomura: Porcellanidae) under laboratory conditions

The complete larval development of the porcellanid crabNeopisosoma negluctum Werding, 1986, was studied under laboratory conditions. At 27°C, the megalopa appeared after 9 days. The development consists of a transitory prezoea, two zoeal stages and a megalopa stage. The larvae exhibit telsonal features which places them in thePetrolisthes-group of porcellanid larvae. Larval morphology gives no additional support for the status ofNeopisosoma as an independent genus.     

Larval salinity tolerance of the South American salt-marsh crab, Neohelice (Chasmagnathus) granulata: physiological constraints to estuarine retention, export and reimmigration

The semiterrestrial crab Neohelice (=Chasmagnathus) granulata (Dana 1851) is a predominant species in brackish salt marshes, mangroves and estuaries. Its larvae are exported towards coastal marine waters. In order to estimate the limits of salinity tolerance constraining larval retention in estuarine habitats, we exposed in laboratory experiments freshly hatched zoeae to six different salinities (5–32‰). At 5‰, the larvae survived for a maximum of 2 weeks, reaching only exceptionally the second zoeal stage, while 38% survived to the megalopa stage at 10‰. Shortest development and negligible mortality occurred at all higher salt concentrations. These observations show that the larvae of N. granulata can tolerate a retention in the mesohaline reaches of estuaries, with a lower limit of ca. 10–15‰. Maximum survival at 25‰ suggests that polyhaline conditions rather than an export to oceanic waters are optimal for successful larval development of this species. In another experiment, we tested the capability of the last zoeal stage (IV) for reimmigration from coastal marine into brackish waters. Stepwise reductions of salinity during this stage allowed for moulting to the megalopa at 4–10‰. Although survival was at these conditions reduced and development delayed, these results suggest that already the zoea-IV stage is able to initiate the reimmigration into estuaries. After further salinity reduction, megalopae survived in this experiment for up to >3 weeks in freshwater, without moulting to juvenile crabs. In a similar experiment starting from the megalopa stage, successful metamorphosis occurred at 4–10‰, and juvenile growth continued in freshwater. Although these juvenile crabs showed significantly enhanced mortality and smaller carapace width compared to a seawater control, our results show that the late larval and early juvenile stages of N. granulata are well adapted for successful recruitment in brackish and even limnetic habitats.     

Ontogeny of osmoregulation and salinity tolerance in a mangrove crab, Sesarma curacaoense (Decapoda: Grapsidae)

The grapsid crab Sesarma curacaoense is believed to represent the closest saltwater relative to the ancestor which gave rise to an adaptive radiation of endemic freshwater and terrestrial species on the island of Jamaica. Living in mangrove swamps with variable salinity conditions and showing semiterrestrial behaviour, S. curacaoense exhibits ecological adaptations to non-marine conditions. In laboratory experiments, we studied the salinity tolerance during development from hatching to the end of the first juvenile stage. Successful development through metamorphosis occurred in the full salinity range tested (15-32 per thousand), although mortality was significantly enhanced and development delayed at 15 per thousand. In another series of experiments, we studied the ontogeny of the capability for osmoregulation, which is considered as the physiological basis of osmotic stress tolerance. Our results show that S. curacaoense is from hatching a fairly strong hyperosmoregulator in dilute media. This capability increased gradually from hatching throughout the larval and juvenile development. In seawater (32 per thousand) and at an enhanced salt concentration (44 per thousand), the zoeal stages remained hyperosmoconformers. The capability for hypoosmoregulation in concentrated media appeared first in the megalopa stage and increased thereafter. Adult crabs were observed to be strong hyper-hypo-osmoregulators in a salinity range from at least 1 per thousand to 44 per thousand. The unusually early appearance of strong regulatory capabilities, particularly in dilute media, is interpreted as a physiological preadaptation that should have facilitated the evolutionary process of adaptive radiation in non-marine environments on Jamaica.     

Physiological and biochemical changes during the larval development of a brachyuran crab reared under constant conditions in the laboratory

Larvae of the spider crabHyas araneus were reared in the laboratory at constant conditions (12°C; 32‰S), and their feeding rate (F), oxygen consumption (R), nitrogen excretion (U), and growth were measured in regular intervals of time during development from hatching to metamorphosis. Growth was measured as dry weight (W), carbon (C), nitrogen (N), hydrogen (H) protein, and lipid. All these physiological and biochemical traits revealed significant changes both from instar to instar and during individual larval moult cycles. AverageF was low in the zoea I, reached a maximum in the zoea II, and decreased again in the megalopa. In the zoeal instars, it showed a bell-shaped pattern, with a maximum in the middle (zoea I) or during the first half of the moult cycle (zoea II). MaximumF in the megalopa was observed still earlier, during postmoult. Respiration (R) increased in the zoeal instars as a linear function of time, whereas it showed a sinusoidal pattern in the megalopa. These findings on variation inF andR during larval development confirm results obtained in previous studies onH. araneus and other decapod species. Excretion (U) was measured for the first time with a high temporal resolution in crab larvae. It showed in all three larval instars a bell-shaped variation pattern, with a maximum near the middle of the moult cycle, and significantly increasing average values from instar to instar. The atomicO/N ratio followed an inverse pattern, suggesting a maximum utilization of protein as a metabolic substrate during intermoult. Growth data from the present study and from a number of previous studies were compiled, showing consistency of growth patterns, but a considerable degree of variability between larvae from different hatches reared under identical conditions. The data show the following consistent tendencies: during the first part of each larval moult cycle (in postmoult, partly in intermoult), lipids are accumulated at a higher rate than protein, whereas an inverse growth patterns is typical of the later (premoult) stages. These two different growth phases are interpreted as periods dominated by reserve accumulation in the hepatopancreas, and epidermal growth and reconstruction (morphogenesis), respectively. Differences between individual larval instars in average biochemical composition and growth patterns may be related to different strategies: the zoeal instars and the early megalopa are pelagic feeding stages, accumulating energy reserves (principally lipids) necessary for the completion of larval development, whereas the later (premoult) megalopa is a semibenthic settling stage that converts a significant part of this energy to epidermal protein. The megalopa shifts in behaviour and energy partitioning from intense feeding activity and body growth to habitat selection and morphogenesis, preparing itself for metamorphosis, i.e. it shows an increasing degree of lecithotrophy. Data from numerous parallel elemental and biochemical analyses are compiled to show quantitative relationships betweenW, C, N, H, lipid, and protein. These regressions may be used as empirical conversion equations for estimates of single chemical components in larvalHyas araneus, and, possibly, other decapods.     

Effects of reduced salinities on metamorphosis of a freshwater-tolerant sesarmid crab, Armases roberti: Is upstream migration in the megalopa stage constrained by increasing osmotic stress?

Numerous species of estuarine and freshwater-tolerant crabs show an “export strategy”, i.e. an early larval downstream transport towards coastal marine waters, later zoeal development at higher salinities, and a return of the last larval stage, the megalopa, into estuaries or rivers. The speed and extent of the upstream migration of the megalopa through strong salinity gradients may be constrained by increasing hypo-osmotic stress. In an experimental laboratory study with Armases roberti, a freshwater-inhabiting sesarmid crab from the Caribbean region, we studied in the megalopa stage (after zoeal rearing at 25‰) the tolerance of reduced salinities.In the first experiment, the larvae were exposed directly to various constant salinities (1-25‰). For the second experiment, they were transferred stepwise to strongly diluted media (within 6 days from 25‰ to ≤ 3‰), simulating differential scenarios of upstream migration into brackish or freshwater habitats.When postmoult megalopae were exposed directly to salinities ≤ 3‰, they all died within 24 h. A slightly higher salt concentration (5‰), however, allowed for considerable survival (46%) through metamorphosis to the first juvenile crab stage. In treatments with continuous exposure to 10-15‰, as well as in a control group (25‰), survival to metamorphosis was significantly higher (83-96%), and the average duration of development was shorter compared to 5‰ (12-13 vs. 16 days). In the second experiment, with stepwise salinity reductions, gradual acclimation to decreasing osmotic pressures permitted a successful development to metamorphosis at ≤ 3‰ and even in freshwater (< 0.2‰).This strong physiological adaptability enables the megalopa of A. roberti to cross during its upstream migration, within a short time (6 days), strong osmotic gradients, so that metamorphosis is possible also in freshwater habitats where the conspecific adult crabs live. The speed of migration appears to be limited by physiological constraints related to changes in the capability for osmoregulation occurring during the course of the moulting cycle.     

Complete larval development of the hermit crabs Clibanarius aequabilis and Clibanarius erythropus (Decapoda: Anomura: Diogenidae), under laboratory conditions, with a revision of the larval features of genus Clibanarius

The complete larval development (four zoeae and one megalopa) of Clibanarius aequabilis and C. erythropus, reared under laboratory conditions, is described and illustrated. The larval stages of the two northeastern Atlantic Clibanarius species cannot be easily differentiated. Their morphological characters are compared with those of other known Clibanarius larvae. The genus Clibanarius is very homogeneous with respect to larval characters. All Clibanarius zoeae display a broad and blunt rostrum, smooth abdominal segments and an antennal scale without a terminal spine. Beyond the second zoeal stage, the fourth telson process is present as a fused spine, and the uropods are biramous. In the fourth larval stage all species display a mandibular palp. The Clibanarius megalopa presents weakly developed or no ocular scales, symmetrical chelipeds, apically curved corneous dactylus in the second and third pereiopods, and 5–11 setae on the posterior margin of the telson. Apart from the number of zoeal stages, Clibanarius species may be separated, beyond the second zoeal stage, by the telson formula and the morphology of the fourth telson process.     

A description of larval and early juvenile development in Paralomis spinosissima (Decapoda: Anomura: Paguroidea: Lithodidae) from South Georgia waters (Southern Ocean)

The early ontogenetic stages of Paralomis spinosissima Birstein and Vinogradow, 1972, are described in detail and illustrated, with notes on morphological variability observed. Larval and early juvenile development was described to the crab I instar reared under controlled conditions of temperature and food supply. The abbreviated larval development invariably passed through two zoeal stages and the benthic megalopa stage. The larval development was completed without food supply, and food Artemia nauplii were first given after moult to the crab-I stage. Simplification and retarded development of the mouthparts are discussed as a function of lecithotrophy of these larvae and based on morphology no facultative feeding mode is suggested. Lecithotrophy in the Southern Ocean Lithodidae is discussed to be an adaptation allowing independence from seasonal food availability at high latitudes.