Megalopa Stage Research Articles

Suspended mesh-bags enclosures for Southern King Crab Lithodes santolla (Molina 1782) larvae and juvenile culture in the sea

The potential for using suspended mesh-bags for larval/juvenile southern king crab (Lithodes santolla) aquaculture was assessed. Three early stages (Zoea, Megalopa and first juvenile, or C1) were confined for 45–65 days in mesh-bags near the sea-bottom. As L. santolla starts feeding when it reaches the first juvenile stage, the effect of biofouling presence was also tested in the C1 culture. Extreme vulnerability of the first larval stage was observed, as no live larvae were recovered when Z1 were used as seeds. On the other hand, survival of Megalopa and C1 reached 19.76 ± 1.08 and 30.00 ± 3.50%, respectively, and both C1 juvenile survival and growth were enhanced significantly by the presence of biofouling on the bags. These results indicate that suspended mesh-bags have potential for L. santolla juvenile culture in the sea. We suggest a 2-step culture process: indoor culturing of the three Zoea stages, and subsequently sea culture starting at the Megalopa stage. Once Megalopa molt to the C1 stage in the field, the already fouled culture system (mesh-bags) would allow newly molted crabs to feed. Further research should be directed towards sea culture optimization, including feeding requirements for bigger crabs, to implement a future stock enhancement program for king crabs in the Beagle Channel.

Ảnh hưởng của việc bổ sung hàm lượng lecithin khác nhau trong thức ăn đến sự biến thái và tỉ lệ sống của cua biển (Scylla paramamosain) từ giai đoạn zoea 3 đến cua 1

The study was conducted to deterimne the suitable supplementation level of lecithin in formulated feeds for larvae of mud crab, Scylla paramamosain consisting of two rearing phases. (1) From zoea 3 to megalopal stage, (2) From megalopal stage to crablet 1. The experiment was completely randomized with 5 replications of five feeding treatments. The test diets had isonitrogenous (53%), isolipid (12%), were supplemented with different lecithin levels of 0% (control diet), 1%, 2%, 3% and 4%. Crab larvae were co-fed Artemia and experimental feeds during larval rearing period. The results showed that when rearing from zoea 3 to megalop stage, which received the diet supplemented with 3% lecithin gave significantly higher larval stage index, survival, length and weight) of megalopa than those in the control diet. When rearing from megalopal stage, the carapace width, weight and survival of crablet1 inthe 3% lecithin group were highest and significantly different from other feeding treatments except the 2% and 4% lecithin treatments for survival. These results suggested that formulated feeds supplemented with 3% lecithin could be considered the suitable level for larval rearing of mud crab S. paramamosain.

Extension of Rotifer (Brachionus Plicatilis) Inclusions in the Larval Diets of Mud Crab, Scylla Paramamosain (Estampodor, 1949): Effects on Survival, Growth, Metamorphosis and Development Time

The study evaluated the effects of extended dietary inclusions of rotifers (Brachionus plicatilis) on the survival, metamorphosis rate, growth and development time in the larvae of mud crabs (Scylla paramamosain). The five most commonly published feeding regimes of mud crab (S. paramamosain) larvae were selected and tested by including rotifers onto them. Mud crab larvae in the first feeding regime were fed exclusively with Artemia nauplii (control or regime A), while those in feeding regimes 2, 3, 4 and 5 were fed rotifers starting from zoea 1 (Z1) to various development stages of mud crab larvae whereas feeding with Artemia nauplii was commenced from the Z2 stage until the end of the trial (megalopa stage). The results of the larval feeding trial for 24 days of culture showed the progressive decrease in survival of the larvae in all feeding regimes. Extended inclusion of rotifer feeding until Z5 stage resulted in significantly higher survival than in the control from 18 day after hatching onwards. Larval survival was negatively correlated (R2 from 0.78 to 0.90) with the rearing time; however, different feeding regimes had no significant effect on this correlation. Extending inclusion of rotifer feeding until the Z3, Z4 and Z5 stages resulted in higher percentages of megalopa metamorphosis than in regime control, but did not significantly impact development time, carapace width, body length and wet weight of megalopa.

Larval development of the symbiotic pea crab Pinnaxodes chilensis (H. Milne Edwards, 1837) (Decapoda, Brachyura, Pinnotheridae) reared in laboratory

The complete larval development of Pinnaxodes chilensis (including four zoeal stages and a megalopa stage) is described and illustrated in detail for the first time. The descriptions are based on laboratory-reared larvae obtained from ovigerous females found inside specimens of the sea urchin Loxechinus albus collected in the coast of Valparaíso, Chile. In order to allow the correct differentiation of specimens from plankton samples, the larval stages of P. chilensis are compared with those from other Pinnotheridae species, whose larval development is known for the Chilean continental waters (Calyptraeotheres politus). The morphological characters described for P. chilensis larvae, as well as the comparison with the remaining larval development descriptions available for the genus Pinnaxodes, are used to discuss the heterogeneity within this genus.

The salinity during larval development affects the dispersion in adults of the tree-climbing crab Aratus pisonii

ABSTRACTAdults of the tree-climbing crab Aratus pisonii occur in estuarine regions with a range of salinity of 0–35. However, the larvae cannot complete the development in a wide range of salinities. A study about the effect of salinity on the larval development was conducted in order to infer about adult dispersion and occurrence in a wide range of salinity. Two experiments were conducted: (1) from zoae I to megalopae stage and (2) from megalopa to juvenile stage. Larvae from eight females from Paranaguá Bay, Paraná, Brazil were obtained. After eclosion, for the first experiment, 100 zoea larvae from five females were acclimated, individualized and transferred to small aquariums with five distinct salinity treatments (S0, S5, S15, S25 and S35). For the second experiment, 50 megalopae from three females were individualized in aquariums in the same salinity treatments. Both experiments were conducted in incubator BOD with a constant temperature of 25°C and photoperiod of 12 hours (light/dark). Larvae were fed daily with eggs and naupli newly hatched of Artemia sp. The salinity affected the survival rate during the development in both experiments. Higher survival from zoea I to megalopa stage occurred in salinities 25 and 35 PSU, while from megalopa to juvenile stage in salinities 15 and 25 PSU. In both experiments the larvae did not tolerate low salinities as adults, with total mortality in S0 and S5. Our results suggest that the species have a larval export strategy of zoae larvae to oceanic regions (higher salinities) and megalopae needed to return to estuarine areas with intermediate salinities to complete the development. The occurrence of adults in estuarine areas with low (< 5 PSU) or high (> 25 PSU) salinities most likely occur after the metamorphosis to the juvenile stage by terrestrial dispersion or at the stage of megalopa (marine dispersion) during favourable weather events.

Larval stages of the crab Mithrax tortugae (Brachyura: Mithracidae) with comparisons between all species of Mithrax

ABSTRACTThe postembryonic larval stages of Mithrax tortugae are described, illustrated and compared with the described zoeae of other Mithrax species. Mithrax tortugae showed morphological features in all the stages of larval development that differed from those observed in other species of Mithrax, especially M. hispidus. In the Zoea I stage, M. tortugae and M. pleuracanthus lacked the minute spine on the dorsal spine observed in M. hispidus; M. tortugae exhibited a terminal spine on the inner lobe of the coxal endite of the maxilla, which was not observed in M. hispidus or M. pleuracanthus. Also, M. tortugae exhibited furcae with spines that are not spinulated, whereas in M. hispidus and M. pleuracanthus these spines are spinulated. In the Zoea II stage, M. tortugae showed a terminal spine on the coxal endite of the maxillula, whereas in M. hispidus and M. pleuracanthus this spine is absent. In the Megalopa stage, we also observed differences in the sternal plate setation between M. tortugae and M. hispidus, where M. tortugae had eight simple setae and M. hispidus showed two simple and four plumodenticulate setae. Partial sequences of the 16S rRNA and COI genes of the parental female were analysed, providing additional evidence for species identification. Together, our analyses of larval morphology and the results of the molecular analyses reinforced recognition of the relationships among M. tortugae, M. hispidus and M. pleuracanthus.

Description of the larval stages of the Red Sea-inhabiting Cymo melanodactylus de Haan, 1833, C. andreossyi (Audouin, 1826) and C. quadrilobatus Miers, 1884 (Decapoda: Brachyura: Xanthidae: Cymoinae) reared under laboratory conditions

Ovigerous females of Cymo melanodactylus, C. andreossyi and C. quadrilobatus were collected from a coral reef, Jeddah (Biadah, Obhur) and Thuwal, Saudi Arabia and reared in the laboratory. The morphological features of the zoea I of C. andreossyi, and zoeae I and II of C. quadrilobatus, as well as the complete larval stages of C. melanodactylus, have been described for the first time. Some characters distinguish these species: cephalothorax size; ratio of the length of antennal protopod and exopod; setations of the endopod of second maxilliped and the presence of a small tooth on the basal endite of the maxillule in the zoea I of C. melanodactylus and C. andreossyi. Morphological features of cephalothorax spines, setations of the endopod of antenna, first and second maxillipeds and the inner spines of telson change as the larval stages of C. melanodactylus progress. The morphological features of the zoeal and megalopal stages of the above-mentioned crabs were compared with those of the larvae of some conspecifics and other xanthid larvae described from the Red Sea. The megalopa of C. melanodactylus can easily be differentiated from those of Chlorodiella nigra and Leptodius exaratus by the setations of the exopod and endopod of antennule, antenna, maxillule and first to third maxillipeds.

The neritic benthopelagic fauna: Which factors explain nocturnal distribution better?

Nocturnal sampling of mesoplankton above different biotopes at depths of 10, 20, and 40m, with a temporal resolution of 10min (98 hauls) was made and 76 taxa were identified. Six environmental factors were tested as the proximate cues for the distribution of individual taxa and integral community parameters: type of sea-floor biotope/depth (SFB), temperature (T), time after sunset (TAS), residual solar illumination, (assessed as time to midnight, TTM), moon phase (MP), and moon altitude (MA). Canonical Correspondence Analyses (CCAs), Bray-Curtis analyses (BCAs), and one-way ANOSIM and SIMPER tests were used to assess the impact of the environmental factors on the distribution of individual taxa, integral community parameters, and community structure. Seventy six taxa were recorded, with 17 taxa, mostly decapod larvae, contributing >1% of the total amount of sampled individuals. Four decapod species comprised over 50% of the total benthopelagic abundance. Decapod larvae migrated as benthopelagic fauna and aggregated over sites where adults live; this behaviour was observed both in zoea and in megalopa stages (ANOVA and SIMPER tests). SFB, T, and TTM are the best proximate cues for the nocturnal distribution of the neritic benthopelagic fauna. Significance of environmental factors may change with depth and sea-floor biotope type: T and TTM are equally important above all explored depths; impact of TAS decreased and contribution of MP and MA increased above greater depths. Further studies of the mesoplanktonic samples, which yield greatly richer material than macroplanktonic samples, may favour this analysis.

Importí­¢ncia do rotí­­fero como alimento no desenvolvimento larval do caranguejo-uçá

O objetivo deste trabalho foi verificar os efeitos da exclusão de rotí­­fero e sua substituição por ração no desenvolvimento, crescimento e sobrevivência de larvas do caranguejo-uçá (Ucides cordatus). As larvas foram cultivadas individualmente e submetidas a seis tratamentos (T1 a T5 e TR), com 50 réplicas, de zoea (Z1 a Z5) até o estágio de megalopa (M). A alimentação foi composta por náuplios de artêmia e microalgas em todos os tratamentos. O rotí­­fero foi introduzido também como alimento de T1 a T5, exceto em TR, em que a ração comercial microparticulada foi administrada como alimento. O rotí­­fero foi então fornecido nos tratamentos T1-Z1, T2-Z2, T3-Z3, T4-Z4 e T5-Z5 e posteriormente excluí­­do. A baixa sobrevivência com reduzido número de megalopas, observada em TR, aponta que a substituição de rotí­­fero por ração não é uma alternativa viável. A exclusão do rotí­­fero pode ser realizada após a mudança para Z2, mantendo o fornecimento de náuplios de artêmia e microalgas, sem impactar no crescimento, sobrevivência e resistência ao estresse, assegurando megalopas com qualidade para repovoamentos e reduzindo, consequentemente, o manejo e custos envolvidos na produção.

Two spliced isoforms of the sex-determination gene fruitless in the Chinese mitten crab Eriocheir sinensis.

The fruitless (fru) gene plays an important role in the sex determination pathway and courtship behavior of Drosophila melanogaster. In the present study, two fru isoforms (Esfru1 and Esfru2) were identified from the Chinese mitten crab Eriocheir sinensis. Sequence analysis showed that Esfru1 and Esfru2 were encoded by the same genomic locus and generated by alternative splicing of pre-mRNA. Esfru1 had all introns completely spliced out, while Esfru2 had a longer exon1 with an additional 78bp sequence. They both contained a conserved BTB domain which was also found in D. melanogaster Fru isoforms. Analysis on temporal expression profiles of Esfru1-2 (a common region of Esfru1 and Esfru2) and Esfru2 (a specific region of Esfru2) showed that they expressed in similar patterns during embryonic development but in different patterns during larval development. The expression of Esfru1-2 decreased gradually from zoea III stage, however, Esfru2 increased from zoea IV stage and reached the peak at megalopa stage. Expression distribution in tissues and in situ hybridization analysis revealed that they showed sexually dimorphic expression in gonads, hepatopancreas and brains. Esfru1-2 showed significantly higher expression in female gonads and hepatopancreas than in males, but highly expressed in male brains than that in females. Interestingly, Esfru2 was displayed in a male-specific manner in each tissue, especially in gonads and hepatopancreas. Our results indicate that Esfru1 might be involved in both sexual brain neuronal structure development and related to female-specific character development. Esfru2 may participate in male-specific character development. This is the first report that characterizes two spliced variants of fru in crustaceans and provides basic information for further functional studies of the crab sex-determination mechanism.

Redescription of the larval stages of Leptodius exaratus (H. Milne Edwards, 1834) from the Red Sea, with notes on the male gonopods

Larvae of Leptodius exaratus from an ovigerous female collected from the intertidal region of North Obhur, Jeddah, Saudi Arabia, were reared in the laboratory up to megalopa stage, and all the larval stages are described and illustrated. Mostly, former descriptions of this species were inconsistent, made about two decades before, and some were incomplete. Therefore, all the zoeal and megalopa stages of L. exaratus are redescribed and illustrated. The morphological features of the larvae of the present study were compared with those of the same species and L. affinis described from worldwide. The male gonopds of L. exaratus collected from the study sites are described and compared with those of the male gonopds of L. exaratus sensu lato described from elsewhere using SEM micrographs.

Thực nghiệm ương ấu trùng cua biển (Scylla paramamosain) san thưa ở các giai đoạn khác nhau

Research on density reduction at different stages of crab larvae was done in order to improve the crab survival rate in nursery. Experiment included 4 treatments and each treatment was triplicated such as (i) density reduction at Zoea-3 stage, (ii) density reduction at Zoea-4 stage, (iii) density reduction at Zoea-5 stage, (iv) density reduction at Megalopa stage. Experimental tanks volume was 0.5m3, larvae density was 300 individuals/L and the salinity was maitained at 30 ‰. When larvae reached the stage of reduction, they were moved to other tanks (2m3, containing 1.5m3 water). After 22 days of rearing, the larval stage index were not significant difference (p>0.05) among treatments, the highest survival rate was 9.8% in treatments with density reduction at Zoea-3 and Zoea-4 stage, it was significantly higher than those in density reduction at Megalopa stage. However, there was no significant difference in survival rate when doing density reduction at Zoea 3, 4 and 5 stages. Results from this study showed that density reduction at Zoea-3 stage or Zoea-4 stage in mud crab larvae rearing obtained the highest results.

Effects of Essential Fatty Acids Containing Natural and Commercial Diets on Larvae Rearing of the Green Mud Crab &lt;i&gt;Scylla Paramamosain&lt;/i&gt; (Estampador 1949)

Effect of essential fatty acids (EFA) on growth and survival of the green mud crab (Scylla paramamosain) larvae was assessed by feeding with natural to commercial diets. The feeding schemes were: larvae reared with Artemia (T1); larvae initially fed with rotifers (up to Z2) and ended (Z3 to megalopa) with Artemia (T2); and larvae fed with rotifers up to Z2 and ended (Z3 to megalopa) with commercial diet (T3). The commercial diet had significantly (p&lt;0.05) higher levels of docosahexaenoic acid (11.23%), ?n-3’s (15.90%) and ?n-6’s (4.21%); and lacked in eicosapentaenoic acid (2.25%) than rotifer and Artemia. The earliest commencement of megalopa stage within 15 days with significantly (p&lt;0.05) higher larval stage index (LSI) of 5.90±0.17 was achieved from the feeding scheme of T2 than other two feeding schemes. This feeding scheme deposited 17.32±0.19% eicosapentaenoic acid (EPA) and 3.82±0.11% docosahexaenoic acid (DHA); the ?n-3 to ?n-6 ratio of 0.20 and EPA to DHA ratio of 0.22 in megalopa, that stimulated significantly higher (p&lt;0.05) megalopa survival (20.00±6.96%) indicating the superiority over rest feeding schemes. Meanwhile, some deformities and mortalities in Z5 and megalopa stages suggested further studies for optimization of specific fatty acid requirements for late larval stages (Z5 and megalopa).

Crablet of Mud Crab Scylla Olivacea Production from the Different Stages of Larvae fed Artemia Nauplii Enriched Using Nannochloropsis sp

Improvement of feed quality for mangrove crab larvae rearing is one of theimportant factors to increase of crablet production. The aim of the research was to knowthe influenzing of enriched Artemia nauplii using Nannochloropsis sp fed to the differentstages of larvae Scylla olivacea on crablet production. Twelve units of tanks volume 250L filled with saline water salinity 30 ppt, aerated, then stocked with new hatched mud crablarvae zoea-1 at the density 100 ind./L. The larvae zoea-1 were fed rotifer, Brachionus sp.and after zoea-3, beside fed by rotifer, the larvae were also fed by Artemia naupli. Fourtreatments were tested, namely: A). Artemia nauplii enriched using Nannochloropsis sp.was given to the larvae zoea-3 until develop to megalop stage. B). Artemia nauplii enrichedusing Nannochloropsis sp was given to the larvae zoea-4 until develop to megalop stage.C). Artemia nauplii enriched using Nannochloropsis sp was given to the larvae zoea-5 stageuntil develop to megalop stage. D). Artemia nauplii without enriched using Nannochloropsissp. was given to the larvae zoea-3 until develop to megalop stage. Result of the researchshowed that the highest of Larvae Development Indexes and Megalop Occurence Indexeswas obtained in treatment A and resulted the highest of crablet production, then followed bytreatment C and B and those were significantly different (P&lt;0.05) with the crablet productionin treatment D. The use of Artemia nauplii enriched by Nannochloropsis sp. to feed larvae,S. olivacea stage zoea-3 to zoea-5 until develop to the megalop stage is one of the key factorto enhance the crablet production. By this finding, the crablet production in hatchery will beincreased and the mud crab culture in brackishwater pond able to developed.

Molecular detection of the parasitic dinoflagellate Hematodinium perezi from blue crabs Callinectes sapidus in Louisiana, USA.

The dinoflagellate Hematodinium perezi is a prolific pathogen of the blue crab Callinectes sapidus along the Atlantic and Gulf of Mexico coasts of North America. High prevalence, sometimes approaching 100%, and outbreaks with high mortality are associated with higher salinities. H. perezi has not been reported previously in blue crabs from Louisiana, USA, where salinities in coastal habitats are generally below the parasite's favorable range. However, the possibility that H. perezi infects blue crabs in higher salinity habitats offshore has not been investigated. A PCR-based test for H. perezi was used to screen blue crabs collected from both high and low salinity areas. These included juvenile and adult crabs from inshore marshes where salinities are relatively low and from higher salinity offshore shoals that are spawning sites for females. H. perezi was detected in blue crabs from offshore shoals (prevalence=5.6%) but not in juvenile or adult crabs from inshore habitats. Megalopae (post-larvae) were also collected from inshore locations. Although megalopae settle inshore where salinities are relatively low, the megalopal stage is preceded by a planktonic phase in higher salinity offshore waters. We detected H. perezi in 11.2% of settling megalopae tested. Although the prevalence of H. perezi was relatively low within our samples, if spawning females and megalopae are especially vulnerable, the impact on the population could be compounded. This is the first report of H. perezi from blue crabs in Louisiana and demonstrates the importance of examining all life stages in determining the prevalence of a harmful parasite.

Effects of lipid enrichment of Artemia nauplii for feeding of spiny lebbeid shrimp, Lebbeus groenlandicus (Fabricius, 1775), zoea larvae

This study was conducted to determine the optimum feed selection for the spiny lebbeid shrimp,Lebbeus groenlandicus, from zoea to megalopa larva. To the shrimp zoeae, untreated hatchingArtemiameta-nauplii, or either of two kinds of enrichedArtemia, were supplied as feed daily, in a concentration of 3 individuals/ml. Throughout the experimental trials, 17.6-18.1 days elapsed until reaching the megalopa larval stage. In the starving trials, no mortality was observed; the mortality values observed in the experimental trials, between 4.8 and 9.5% were considered low and not significantly different (). Neither fatty nor amino acids varied significantly in the zoea I and II stages in either the feeding or starving trials. Highly unsaturated fatty acids and amino acids were significantly lower in the megalopa stage in the starving group, compared with the feeding groups (). Therefore, feeding was proven not to have any effect in the zoea I and II larval stages. However, for the megalopa larval stage, a feed containing supplementary amino acids and fatty acids evoked a positive effect.

Emigration behavior and molting during the sea‐to‐land transition of terrestrial hermit crabs under laboratory conditions

AbstractTerrestrial hermit crabs in the family Coenobitidae (genera Coenobita and Birgus) must migrate onto land after completing a pelagic larval stage in the ocean. Better knowledge of emigration behavior would assist in the conservation and management of coenobitid populations by helping identify and protect the habitats they need to complete their life cycles. We cultured laboratory‐born individuals of five coenobitid species (Coenobita cavipes, C. purpureus, C. rugosus, C. violascens, and Birgus latro) from megalopae to early juveniles (first, second, and/or third crabs) in vessels containing seawater and a hard substrate, and analyzed their behavior and molting in conjunction with our published data for C. brevimanus. Our results confirm that the coenobitids migrated from sea to land at the megalopal stage. Megalopae and early juveniles tended to select shells based on their body size. Inland‐dwelling coenobitids, such as C. brevimanus, C. cavipes, and B. latro, had a longer duration from landing to first molt and had a prolonged first crab intermolt period compared with those of the beach‐dwelling coenobitids C. purpureus, C. rugosus, and C. violascens, probably because of the adaptive traits for migrating to inland habitats. Little burrowing behavior was observed by megalopae of B. latro, but they had a strong tendency to be cryptic under shelters. Additionally, megalopae and early juveniles of Coenobita spp. created and utilized burrows somewhat differently. Our results suggest that coenobitids require specific microhabitats for completing their early life stages in the wild. In particular, megalopae of B. latro may need structurally complex refuges to migrate from the sea.

The Effects of Temperature and Salinity on the Survival, Growth and Duration of the Larval Development of the Common Spider CrabMaja brachydactyla(Balss, 1922) (Brachyura: Majidae)

The effect of temperature and salinity on the larval development of the common spider crab Maja brachydactyla (Balss, 1922) were studied in the laboratory. Larvae were reared at different salinities (0–45) at constant temperature, and under six different combinations of temperature (18 and 21°C) and salinity (30, 35, and 40). The survival and developmental time from newly hatched zoeae to the megalopa stage and from megalopa to the first juvenile stage was quantified; the 24 h median lethal salinity (LS50) for first zoeal stage was calculated. Dry mass (DM), elemental body composition (Carbon, Hydrogen, Nitrogen) and carbon: nitrogen ratio (C:N) were determined in both starved and nourished zoeae. The lower and upper LS50 for M. brachydactyla first zoea in 24 h were 19.9 and 56.0, respectively; similar to other marine stenohaline brachyuran larvae. The megalopa stage was reached in a salinity range from 30 to 40. The highest survival rates to the first juvenile stage were observed at salinity: 35 and temperature: 21°C. Salinity was the key parameter for the survival to first juvenile, whereas the temperature had a higher effect over the duration of the larval development. The greatest loss of DM in starving and nourished zoeae was observed at low salinity (25). No differences were found in DM or C:N during the megalopa stage. The culture and ecological implications of the salinity tolerance of M. brachydactyla larvae are discussed.

Temperature-Dependent Growth and Molting in Early Juvenile Blue CrabsCallinectes sapidus

ABSTRACT Understanding how growth rates are influenced by environmental conditions is important for proper management of commercially harvested species, especially under current and predicted future conditions of global climate change. Blue crabs are of high commercial value in the United States, but are declining in number throughout their range. Previous laboratory and field studies suggest that temperature and salinity play a role in blue crab growth rates, although the results of these studies have been inconclusive and, in some cases, contradictory. Furthermore, these studies have focused primarily on later juvenile stages [>20 mm carapace width (CW)]. This study examined the effects of temperature and salinity on early juvenile (∼2.5–16 mm CW) blue crab Callinectes sapidus growth rates. Crabs were reared in the laboratory under six different temperature and salinity treatments from the megalopal stage until the sixth juvenile instar. Compared with crabs reared at lower temperature, crabs reared at h...

Foregut morphology and ontogeny of the spider crab Maja brachydactyla (Brachyura, Majoidea, Majidae)

We describe the morphology of the foregut of the spider crab Maja brachydactyla Balss, 1922, from first larval stage to adult, with detailed stage-specific documentation using light and scanning electron microscopy. A total of 40 ossicles have been identified in the foregut of adults of M. brachydactyla using Alizarin-Red staining. The morphological pattern of the ossicles and gastric mill is very similar to other Majoidea species with only a few variations. The foregut of the zoeae stages appeared as a small and simple cavity, with a cardio-pyloric valve that separates the stomach into cardiac and pyloric regions. The pyloric filter is present from the first zoea, in contrast to the brachyuran species which have an extended larval development. Calcified structures have been identified in the cardio-pyloric valve and pyloric region of the zoeal stages. The most significant changes in foregut morphology take place after the metamorphosis from ZII to megalopa, including the occurrence of the gastric mill. In the megalopa stage, the foregut ossicles are recognizable by their organization and general morphology, but are different from the adult phase in shape and number. Moreover, the gastric teeth show important differences: the cusps of the lateral teeth are sharp (no molariform); the dorsal tooth have a small, dentate cusp (not a well-developed quadrangular cusp); and the accessory teeth are composed of one sharp peak (instead of four sharp peaks). The gastric mill ontogeny from megalopa to adult reveals intermediate morphologies during the earlier juvenile stages. The relationship between gastric mill structures with food preferences and their contribution to the brachyuran phylogeny are briefly discussed.