Morphological features of the larvae of spider crab <Emphasis Type="Italic">Pugettia quadridens</Emphasis> (Decapoda: Majidae) from the Northwestern Sea of Japan

The entire cycle of larval development of the spider crab Pugettia quadridens (de Haan, 1850) (Decapoda: Majidae), widespread in Peter the Great Bay (Sea of Japan) is studied under the laboratory conditions. The development cycle of this species comprises prezoea, zoea I, zoea II, and megalopa. At a temperature of 18–20° C larval development took from 11 to 15 days. Zoea II is described in detail for the first time. Many morphological characters are found distinguishing zoea and megalopa of P. Quadridens in Russian waters from the larvae of this species in Japanese and Korean waters. Some characters of larvae are similar in P. Quadridens and the related species of the genus Pugettia. The larvae of P. Quadridens occur in the plankton of Vostok Bay from late June to late October with a density up to 5 ind/m³ at a surface water temperature of 13–21°C. They are easily distinguished from the other brachyuran larvae of this region by the absence of lateral spines on the carapace.Original Russian Text Copyright © 2004 by Biologiya Morya, Kornienko, Korn.     

Hot and salty: the temperature and salinity preferences of a temperate estuarine shrimp larva, Upogebia pusilla (Decapoda: Thalassinidea)

At a time when global climate changes are forcing life to adapt to a warming and salinity-changing environment, it is essential to understand how future changes in ocean chemistry will affect species. This study evaluates the combined effects of temperature and salinity on survival and development of Upogebia pusilla larvae. Combinations were made from three temperatures (18, 23, and 28°C) and three salinities (15, 25, and 35). Survival, larval duration and megalopa size were compared between treatments. U. pusilla larvae developed optimally in the highest salinity (35) and higher temperatures (23–28°C). Low salinities and temperatures did not support larval survival and development, with salinity being the main restricting factor for survival, while temperature affected mainly the duration of the larval stages. Larvae at higher temperatures (23–28°C) presented a higher development rate but no differences were found in megalopa size.     

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.     

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.

     

Neurogenesis in larval stages of the spider crab Hyas araneus (Decapoda,Brachyura): proliferation of neuroblasts in the ventral nerve cord

Larvae of the spider crab Hyas araneus were reared in the laboratory from hatching through to metamorphosis. Neurogenesis was recorded in the ventral nerve cord during development of successive larval stages, zoea 1, zoea 2, megalopa and crab 1. Proliferating cells were detected immunocytochemically after in vivo labelling with 5-bromo-2-deoxyuridine (BrdU) which, as a thymidine analogue, is incorporated into the DNA of dividing cells. Segmental sets of mitotically highly active neuroblasts were found in newly hatched larvae. A dorsal neuroblast, a ventral-median neuroblast, 3–6 anterior-ventral neuroblasts and 1–3 lateral neuroblasts could be distinguished in each thoracic ganglion. Significantly fewer neuroblasts were labelled in the suboesophageal ganglion as compared to the thoracic ganglia. The number of active labelled neuroblasts was high throughout zoea 1 and about 30% of zoea 2 development and then dramatically decreased towards premetamorphosis. In the newly moulted megalopa, only a reduced set of neuroblasts was labelled which ceased dividing within the first few days of megalopa development. There is an indication that, although most ganglion mother cells born by unequal division of neuroblasts may go through their final division at an early stage, certain clusters of ganglion mother cells obviously delay their final mitosis. These results are discussed with regard to neuronal integration which necessarily changes during the course of metamorphosis in relation to the altered behavioural repertoire of the larvae.     

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.     

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.     

Behavioural significance of pressure responses in megalopa larvae of Callinectes sapidus and Macropipus sp.

The primarily benthic megalopa larvae of Callinectes sapidus and Macropipus holsatus swim upwards for a short distance from the bottom when subjected to pressure increased above ambient values, particularly when illuminated from above. Larvae exposed to stepwise increments of pressure exhibit a threshold in the barokinetic response which is lower in Callinectes (0.4 atm) than in Macropipus (0.8–1.0 atm). Such behaviour would tend to inhibit swimming in surface waters of stratified estuaries where net flow is seawards, but would promote slight upward swimming when on the bottom in deeper water which has a net flow inwards, thus substantiating other evidence that the megalopa is a stage at which recruitment to estuaries takes place. The lower threshold of the barokinetic response in Callinectes may be related to its occurrence in more uniformly shallow estuaries on the south and east coasts of N. America.

In both species swimming is markedly inhibited after a slight reduction in pressure. Such responses would be of value to larvae running the risk of being washed ashore in surf Sudden reductions in pressure by surf action would induce sinking into the undertow which would carry larvae offshore into deeper water.     

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.     

Nutritional requirements during larval development of the portunid crab,Callinectes sapidus Rathbun

Three kinds of diet were used to identify the critical periods of nutritional vulnerability during larval development of the portunid crab, Callinectes sapidus Rathbun. A diet consisting solely of the rotifer Brachionus plicatilis Müller is not sufficient for complete developmetn. Development to metamorphosis can occur if rotifers are replaced by Day 15 with Artemia salina L. nauplii, but a diet of A. salina between Days 15 and 21 is also not sufficient for complete development. Delay in giving a brine shrimp diet beyond Day 15 causes a reduction in survival to the megalopa with an apparent threshold between Days 22 and 29, delay in molting in late instars, and increased frequency of supernumeracy larvae, many of which molt subsequently to the megalopa. Development to the megalopa on the rotifer diet is possible if crab larvae are initially fed a favorable control diet for as little as 14 days after hatching. Extension of time on the control increases survival to the megalopa slightly, has little effect on molt frequency, but reduces the number of zoeal instars.These data are interpreted in the context of identification of the unknown dietary requirement and for its implication to evolution of reproduction in the Brachyura.     

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     

Occurrence of an alternative pathway in the larval development of the crab Chasmagnathus granulata Dana, 1851 under laboratory conditions

Larvae of the crab Chasmagnathus granulata were collected in a salt marsh located in the Lagoa dos Patos, Brazil and reared from eclosion to metamorphosis under different dietary regimes. Larvae reared individually in beakers of 40 ml and fed Tetraselmis chuii (zoea III and zoea IV), showed a supplementary stage, here designated as zoea V, with morphological characteristics intermediary between zoea IV and megalopa. No zoeae V molted to megalopa stage. To confirm the occurrence of the supplementary stage, mass cultures of larvae of C. granulata were fed Artemia sp. at high densities, we again detected the fifth zoeal instar. However, when zoeae V were individually placed in beakers and fed Artemia nauplii, they succeeded in molting into megalopae. We observed the occurrence of two types of zoeae IV — a smaller type (from which originated the zoeae V) and a larger type (which directly developed into megalopae). We conclude that stressful nutritional/environmental conditions were responsible for the occurrence of this alternative path of development.     

Larval development of Brachynotus gemmellari (Rizza, 1839) (Brachyura, Grapsidae) reared under laboratory conditions

The complete larval development of the grapsid crab Brachynorusgemmellari (Rizza, 1839) was obtained by culture in the Iabomtoiy.Five zoeal stages, the megalopa and the first crab stage aredescribed and illustrated. Larval development from hatchingto first crab took 26 days at 20C. The morphological charaeiarsof the larvae of B.gemmellari are compared with those of otherknown larvae of the genus Brachynosus.     

Methodical aspects of rearing decapod larvae,Pagurus bernhardus (Paguridae) andCarcinus maenas (Portunidae)

Improved methods for experimental rearing ofPagurus bernhardus andCarcinus maenas larvae are presented. Isolated maintenance was found essential for reliable statistical evaluation of results obtained from stages older than zoea-1. Only by isolated rearing is it possible to calculate mean values ±95% confidence intervals of stage duration. Mean values (without confidence intervals) can only be given for group-reared larvae if mortality is zero. Compared to group rearing, isolated rearing led to better survival, shorter periods of development and stimulated growth. Due to different swimming behaviorP. bernhardus zoeae needed larger water volumes thanCarcinus maenas larvae.P. bernhardus zoeae were reared with best results when isolated in Petri dishes (ca. 50 ml). They fed on newly hatched brine shrimp nauplii (Artemia spp.).P. bernhardus megalopa did not require any gastropod shell or substratum; it developed best in glass vials without any food.C. maenas larvae could be reared most sucessfully in glass vials (ca 20 ml) under a simulated day-night regime (LD 16:8); constant darkness had a detrimental effect on development, leading to prolonged stage-duration times.C. maenas larvae were fed a mixture of newly hatched brine shrimp naupli and rotifers (Brachionus plicatilis).     

Complete larval and early juvenile development of the mangrove crab Perisesarma fasciatum (Crustacea: Brachyura: Sesarmidae) from Singapore, with a larval comparison of Parasesarma and Perisesarma

The complete larval development of the sesarmid crab Perisesarmafasciatum (Lanchester, 1900) from Singapore was obtained fromlaboratory culture. All four zoeal stages, the megalopa andthe first crab stage are described and illustrated. The morphologicalcharacteristics of the larvae of P. fasciatum are compared withthose of other known larvae of the genera Perisesarma and Parasesarma.The larval morphology of P. fasciatum clearly presents the typicalcombination of features that characterize sesarmid larvae. Overall,larval stages are very similar in Perisesarma and Parasesarmaand it is impossible to distinguish these two genera by larvalmorphology.     

Neurogenesis in the developing crab brain: Postembryonic generation of neurons persists beyond metamorphosis

A considerable amount of information is available about the structure and function of the central nervous system in adult crustaceans. However, little effort has been directed toward understanding embryonic and larval neurogenesis in these animals. In the present study we recorded neurogenesis in the brain of laboratory-reared larvae of the spider crab Hyas araneus. Proliferating cells were detected immunocytochemically after in vivo labeling with 5-bromo-2′-deoxyuridine. This method has already been used to study the proliferation of neuroblasts in the ventral nerve cord of spider crab larvae. In the brain, a set of mitotically highly active neuroblasts was found in newly hatched zoea 1 larvae. These neuroblasts are individually identifiable due to their position and therefore a schematic map of the cerebral neuroblasts could be established. The number of active neuroblasts is high from hatching throughout the molt to the zoea 2. This proliferative action then decreases dramatically and has ceased at the time of first metamorphosis toward the megalopa larva. However, many ganglion mother cells born by unequal division of neuroblasts then go through their final division throughout the subsequent megalopa stage. In the brain, all mitotic activity has ceased at the time of second metamorphosis with the exception of a cluster of labeled nuclei within the olfactory lobe cells. In this cluster, the generation of neurons persists beyond the second metamorphosis into the crab 1 stage. Meanwhile, the neuropil volume of the olfactory lobes increases 10-fold from hatching to the crab 1. These results are discussed with regard to reports on neuronal proliferation during adult life in insects and rodents. © 1996 John Wiley & Sons, Inc.