The structure and cytochemistry of the neurosecretory cells in Ocypoda platytarsis Milne Edwards (Crustacea: Brachyura).

Four types of NS cells ('A', 'B', 'C' and 'D') in the brain, thoracic ganglion and four types ('alpha', 'beta', 'gamma' and 'delta') in the eye-stalk of Ocypoda platytarsis have been encountered. The cells in the brain occur in groups. Five groups have been noticed in the brain. Of the five groups the ventro-median group is unpaired and homogenous. In the other four one is unpaired and three are paired, and all are heterogenous. In the eyestalk the NS cells are distributed in 6 groups. They are MEX1, MIX1, MTX1, MTX2, MTX3 and MTX4. Of these MEX1 and MTX4 are homogenous. A battery of histochemical tests applied to NS cells revealed that the NS material is rich in carbohydrate moiety, disulfide groups, lipids, phospholipids and RNA. It contains little sulfhydryl groups, protein bound NH2 groups and no tyrosine, tryptophan and arginine.     

On the Androgenic Gland of the Ghost Crab Ocypoda platytarsis M. Edwards (Crustacea: Brachyura)

The morphology and structural peculiarities of the androgenic gland in Ocypoda platytarsis are described. Three types of histologically different cells have been noticed. The histological variations have been attributed to the secretory cycle. Evidence is given for the amitotic division of the cells. Evidences are also given for the holocrine activity of the cells. It has been shown that the growth of the male reproductive system parallels that of the androgenic gland.     

Vertical distribution by demographic groups of ghost crab Ocypode quadrata (Crustacea: Brachyura)

The ghost crab Ocypode quadrata plays an important role in energy transfer between trophic levels, and has been widely used in evaluations of impacted environments. In order to provide data on the biology of this potential bioindicator species, the population structure and vertical distribution of individuals were studied on two beaches in southeastern Brazil. Each beach was divided into quadrants of 1000 m² with boundaries of upper, middle and lower levels in relation to the waterline. Collected monthly by active searching through one year, the specimens of O. quadrata were sexed, measured for carapace width, and returned to the beach. Of the total of 1904 specimens collected, the largest proportion (46.2%) were males, followed by 31.4% juveniles. The vertical distribution of the ghost crabs differed among age groups: males mostly occupied the middle and upper levels; adult females, ovigerous or not, were more abundant in the lower level; and juveniles were evenly distributed in all levels, with a slight tendency toward the middle. The sex ratio favored males in a few months of the year and in the larger size classes. The abundance of O. quadrata is limited by low temperatures, and its spatial and temporal distribution is controlled by food availability and ease of reproduction. Knowledge of the biology of these crabs is essential in order to use them as a bioindicator species; the vertical distribution patterns may reflect changes in the beach hydrodynamics or other environmental factors.     

Leverage and muscle type in crab chelae (Crustacea: Brachyura)

The chelae of Cancer pagurus and Macropipus depurator were examined with respect to mechanical advantage. The closer muscles were investigated with respect to sarcomere length in the constituent fibres and to the force developed by the whole muscle during isometric contraction. Cancer chelae have a relatively high mechanical advantage, 0.329 ± 001. Cancer closer muscles contain a high proportion of fibres with long sarcomeres, mean lengths mostly falling between 12 and 15 μm, and develop a maximum stress of about 496 kN.m⁻² during contraction. These figures are typical for "slow" crustacean muscle. The chelae of M. depurator are dimorphic. In one, the strong chela, the mechanical advantage is 0.248 ± 0.066 while in the other, the fast chela, the mechanical advantage is 0.177 ± 0.006. M. depurator closer muscles contain fibres with mean sarcomere lengths mostly falling between 6 and 10 μm. The muscle develops a maximum stress of about 145 kN.m⁻² during contraction. These figures are typical of "intermediate" crustacean muscles. "Fast" muscle fibres with short sarcomeres (about 30 um) were found in the chelae of both Cancer and M. depurator but were much commoner in the latter. Thus in Cancer a high mechanical advantage is correlated with slow muscle while in M. depurator lower mechanical advantages are broadly correlated with faster muscle. Consistent correlation between mechanical advantage and muscle type in the dimorphic chelae of M. depurator , however, is lacking. No consistent regionation of fibres with similar properties was found in the muscles.     

Triacylglycerol synthesis in the premolt field crab Paratelphusa hydrodromus (Milne-Edwards) (Crustacea)

Triacylglycerol synthesis was investigated in the hepatopancreas of the premolt field crab Paratelphusa hydrodromus using uniformally labelled [14C] acetate. Maximum incorporation occurred after 180 min into the triacylglycerol fraction of the hepatopancreas in both the sexes. Sexual dimorphism was indicated by a greater accumulation of labelled acetate in the triacylglycerol fraction of the hepatopancreas of the female than that of the male crab. The conversion of labelled acetate to triacylglycerol was greater in fed- than starved crabs. Haemolymph seemed to contain factor(s) which enhanced the lipogenic capacity of the hepatopancreas.     

Glycolytic enzymes in the premolt field crab Paratelphusa hydrodromus (Milne-Edwards) (Crustacea)

The quantitative assay of hexokinase (HK), phosphorylase, phosphofructokinase (PFK), glucose 6-phosphate dehydrogenase (G-6-PDH), glycerol 3-phosphate dehydrogenase (G-3 PDH) and lactate dehydrogenase (LDH) revealed that coxal muscles compared to hepatopancreas contained higher activities of all the enzymes investigated. It appears that the coxal muscles of the premolt field crab has carbohydrate-based fuel economy. The hepatopancreas is a rich source of lipid and very poor source of glycogen. The activity of G-6-PDH is moderately high in the hepatopancreas. It seems that in this lipogenic tissue conversion of G-6-P to triose phosphate occurs predominately via pentose-phosphate pathway thus generating NADPH for lipogenesis. The relative G-3PDH ad LDH activities in hepatopancreas and coxal muscles led us to believe that the reconversion of NAD from NADH in hepatopancreas nd muscle flexor is effected by glycerol 3-phosphate shuttle, whereas in muscle extensor it is achieved by both G-3PDH and LDH activities.     

Size-related mating success in the shore crab Carcinus maenas (Crustacea: Brachyura)

The relationship between the size of a given mating male Carcinus maenas (L.) (Brachyura, Portunidae) and the size of the female with which it was paired was studied for 1248 pairs of crabs collected from the shore In 764 of these pairs the female was in pre-moult and so the pair were in pre-copula. In the remaining 484 pairs the female had already moulted and the pairs were in copula. There were significant correlations between the sizes of the males and females in both pre-copula and copula pairs. It was found that male Carcinus collected in mating pairs and tested in the laboratory were unable to distinguish between females in terms of their size or stage of pre-moult. The positive correlation between the sizes of males and females in mating pairs on the shore is proposed to be, in part, a function of a mechanical constraint of the size of female that a given male can hold, defend and copulate with. In addition, encounters between solitary males and males carrying females, resulting in the formation of new pairs, appear to enhance the size-related mating pattern observed.     

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.     

Heterochely and handedness in the shore crab Carcinus maenas (L.) (Crustacea: Brachyura)

A large sample ofadult male Carcinus maenas was 79% right-handed and 21% left-handed. A separate sample of 207 intact adult males was divided into left-handed and right-handed crabs and four measurements were taken from all major and minor chelae. Correlation and regression analyses against carapace width on log-transformed data showed that major chelae of right-handed crabs grow proportionately higher with increasing size and the ideal mechanical advantage increases; concurrently, the fingers of the minor chelae grow proportionately longer. The data for left-handed crabs showed greater variability, especially for minor chelae, providing evidence for the concept that left-handedness arises by reversal of handedness following loss of the major chela from the right-hand side. Records of handedness in large samples of non-ocypodid heterochelous brachyuran crabs show a preponderance of right-handedness.     

Cytochemistry of the neurosecretory cells in the crab Menippe rumphii (Fabricius, Crustacea: Brachyura)

In Menippe rumphii five types of neurosecretory cells are found in the cerebral, commissural and thoracic ganglia. Detailed cytochemical observations on the neurosecretory cells revealed that they have responded strongly to saliva resistant PAS staining. Among proteins those rich in disulfides and sulhydryl groups are observed. Greater amounts of cytoplasmic RNA are observed in the reproductive season. Considerable amounts of lipids and phospholipids are also observed in the AS cells. The cytochemical differences between the NS cells and the nonsecretory neurons are also discussed.     

Phylogenetics of Cancer crabs (Crustacea: Decapoda: Brachyura).

We used morphological, mitochondrial DNA sequence, paleontological, and biogeographical information to examine the evolutionary history of crabs of the genus Cancer. Phylogenies inferred from adult morphology and DNA sequence of the cytochrome oxidase I (COI) gene were each well resolved and well supported, but differed substantially in topology. Four lines of evidence suggested that the COI data set accurately reflected Cancer phylogeny: (1) in the phylogeny inferred from morphological data, each Atlantic species was sister taxon to an ecologically similar Pacific species, suggesting convergence in morphology; (2) a single trans-Arctic dispersal event, as indicated by the phylogeny inferred from COI, is more parsimonious than two such dispersal events, as inferred from morphology; (3) test and application of a maximum likelihood molecular clock to the COI data yielded estimates of origin and speciation times that fit well with the fossil record; and (4) the tree inferred from the combined COI and morphology data was closely similar to the trees inferred from COI, although notably less well supported by the bootstrap. The phylogeny inferred from maximum likelihood analysis of COI suggested that Cancer originated in the North Pacific in the early Miocene, that the Atlantic species arose from a North Pacific ancestor, and that Cancer crabs invaded the Atlantic from the North Pacific 6-12 mya. This inferred invasion time is notably prior to most estimates of the date of submergence of the Bering Strait and the trans-Arctic interchange, but it agrees with fossil evidence placing at least one Cancer species in the Atlantic about 8 mya.     

Estimating abundance and spatial distribution patterns of the bubble crab Dotilla fenestrata (Crustacea: Brachyura)

Abstract The bubble crab Dotilla fenestrata forms very dense populations on the sand flats of the eastern coast of Inhaca Island, Mozambique, making it an interesting biological model to examine spatial distribution patterns and test the relative efficiency of common sampling methods. Due to its apparent ecological importance within the sandy intertidal community, understanding the factors ruling the dynamics of Dotilla populations is also a key issue. In this study, different techniques of estimating crab density are described, and the trends of spatial distribution of the different population categories are shown. The studied populations are arranged in discrete patches located at the well‐drained crests of nearly parallel mega sand ripples. For a given sample size, there was an obvious gain in precision by using a stratified random sampling technique, considering discrete patches as strata, compared to the simple random design. Density average and variance differed considerably among patches since juveniles and ovigerous females were found clumped, with higher densities at the lower and upper shore levels, respectively. Burrow counting was found to be an adequate method for large‐scale sampling, although consistently underestimating actual crab density by nearly half. Regression analyses suggested that crabs smaller than 2.9 mm carapace width tend to be undetected in visual burrow counts. A visual survey of sampling plots over several patches of a large Dotilla population showed that crab density varied in an interesting oscillating pattern, apparently following the topography of the sand flat. Patches extending to the lower shore contained higher densities than those mostly covering the higher shore. Within‐patch density variability also pointed to the same trend, but the density increment towards the lowest shore level varied greatly among the patches compared.     

Observations on the nature of neurosecretion in the marine crab Portunus sanguinolentus (Herbst) (Crustacea: Brachyura)

Several types of NS cells were identified in Portunus sanguinolentus--five types (A, A', B, C and D) in the brain and thoracic ganglion, four types (A, B, C and D) in the commissural ganglia and four types (alpha, beta, gamma and delta) in the optic ganglia. The distribution of these NS cells is described. Cytochemically, the neurosecretory material in the NS cells has a carbohydrate moiety and is rich in disulphide groups, lipids, phospholipids and RNA. It contains a small amount of sulphydryl groups and protein-bound NH2 groups, but no tyrosine or tryptophan. The NS activity of the brain was found to be closely associated with the reproductive and moult cycles. Just before the initiation of vitellogenesis and moulting the NS cells display secretory hyperactivity. Axonal transport of NS material was also observed in the NS cells.     

Aspects of the biology of the deep-sea spider crab, Dorhynchus thomsoni (Crustacea: Brachyura)

Pelagic first crab stages of the deep-sea spider crab, Dorhynchus thomsoni , are reported from mid-water samples taken at a variety of localities in the Porcupine Seabight and the Rockall Trough. Some of these samples were from hauls made near the surface over depths of 3000 m or more.
An analysis of these pelagic samples, and of benthic catches of D. thomsoni held by the Institute of Oceanographic Sciences and the British Museum (Natural History), indicate that most females and at least some males undergo the puberty prior to the third crab instar, these individuals therefore probably pass through a total of only three larval and three post-laval instars. There is at least a possibility that some individuals moult after the moult of puberty, unlike any other spider crabs.     

Description of a new species of deep-water crab of the genus Homolodromia A. Milne-Edwards, 1880 from the northern Indian Ocean (Crustacea: Decapoda: Brachyura: Homolodromiidae)

ABSTRACT

Homolodromia rajeevani, a new species of deep-water homolodromiid sponge crab, is described from the northern Indian Ocean (Arabian Sea, depth 957 m, and Bay of Bengal, 645 m), and is the first record of the genus from the area. This species resembles the western Indian Ocean species, namely, Homolodromia bouvieri Doflein, 1904, in having 2 terminal spines on the propodi of the last two pereopods, but can be easily distinguished from the latter species by the inflated carapace, simple long setae on carapace and appendages, slender pseudo-rostral spines separated by a U-shaped base, and a slender arched dactylus of cheliped with maximum elevation at proximal part which bears broadly circular depressions with sparse setae. The most diagnostic character is the higher number of spines on the occlusal surfaces of propodal thumbs and dactyli of the pseudochela of the last two pereopods as compared to H. bouvieri. A key for the identification of the species under the genus Homolodromia is also provided.

http://zoobank.org/urn:lsid:zoobank.org:pub:48894F49-5124-4723-9FF2-3D30FB536DA5     

Histological and histochemical studies on regeneration and tissue differentiation in the crab Menippe rumphii (Fabricius) (Crustacea: Brachyura)

In the process of regeneration the crab secretes an outer three-layered fibrous exoskeleton, consisting of outer thin parenchymatous vacuolated layer, an elastin layer, and a collagen layer. The origin and synthesis of these layers have been discussed. Similarly a two-layered inner cuticle is also secreted during the process of regeneration. Together with this, tissue differentiation takes place inside the growing limb bud. The rôles of the cells responsible for the secretion of the outer and inner cuticular layers have been discussed. Various histochemical tests have been employed to study the chemical nature of the cuticular layers, connective tissue cells, tegumental glands, and haemocytes. Two types of connective tissue cells and four types of haemocytes were identified. The rôles of the haemocytes, tegumental glands, and connective tissue cells in tissue differentiation are also discussed.     

Histochemistry of the cuticle of the crab Menippe rumphii (Fabricius) (Crustacea: Brachyura) in relation to moulting

Histological and histochemical methods have been employed to study the formation and growth of the exoskeleton in relation to the moulting cycle of the crab Menippe rumphii (Fabricius). In the premoult condition the epidermal cells secrete a two-layered cuticle. Later these layers are widened by the secretions coming from the reserve cells, tegumental glands, and the Leydig cells. The fully formed cuticle of the intermoult crab is divisible into four layers, epicuticle, exocuticle, mesocuticle, and endocuticle.Histochemical observations on different cells have revealed that the tegumental glands secrete both neutral and acid mucopolysaccharides. The reserve cells are positive to PAS, BPB, Sudan Black B and Alizarin Red S techniques indicating the presence of carbohydrates, proteins, lipids, and mineral calcium. The Leydig cells are loaded with enzymes, including alkaline phosphatase, acid phosphatase, lipase, and phenoloxidase. Other histochemical tests have been employed to investigate the formation of different layers of the cuticle.     

Morphology of the female genital ducts of the blue land crab Cardisoma guanhumi (Crustacea: Brachyura: Gecarcinidae)

This is a histological and histochemical analysis of the terminal portion of the female reproductive system and genital ducts of the blue land crab (Cardisoma guanhumi). Animals were collected in the Jaguaribe estuary (Ceará, Brazil) and dissected. Genital duct fragments were fixed and submitted to different staining techniques. The female reproductive system consists of a pair of ovaries and a pair of genital ducts. In the mid‐posterior portion of each lobe, the ovaries communicate with the genital ducts, which are subdivided into oviduct, spermatheca, vagina, and gonopore. Histologically, the spermatheca of C. guanhumi is composed of columnar secretory epithelium and is divided into a dorsal zone and a ventral zone, the latter covered internally by a cuticle layer. Both zones are enveloped by a thin layer of loose connective tissue. Histological cross sections revealed the vagina to be concave, a pattern considered phylogenetically more advanced than the simple, tubular form. Our findings suggest fertilization is internal, favoring sperm from the most recent copulation.     

Structure and function of the chelae and chela closer muscles of the shore crab Carcinus maenas (Crustacea: Brachyura)

Major and minor chelae of Carcinus maenas were investigated with respect to mechanical advantage, angles of pennation and sarcomere lengths of the closer muscle fibres, maximum pinching forces induced by nervous stimulation and maximum stress in the closer muscles. Major chelae differed from minor chelae in all these factors. Mean mechanical advantages of major and minor chelae were 0·36 and 0·26, respectively. Angles of pennation were greater at the distal ends of closer muscles and declined proximally: in half open major and minor chelae distal to proximal angles were about 35–26° and 29–19°, respectively. Mean sarcomere lengths in closer muscles of fully closed major and minor chelae were significantly different at 7·6 and 6·0 fim, respectively; there was great variation within chelae and between crabs. Major chelae pinched more strongly than minor chelae due to higher mechanical advantages, larger closer apodemes and greater stress in the muscle. Mean maximum stresses in major and minor chelae were 677 and 474 kN/m², respectively. The biggest stress recorded–1057 kN rrr²–was in a major chela. Pinching forces induced by injecting a high K⁺ and caffeine ringer were about 20% weaker than nervously stimulated pinches.