Innervation of the limb accessory flexor muscle in several decapod crustaceans. I. Anatomy

The innervation of the accessory flexor muscle of the limbs of several decapod crustaceans was studied by means of vital staining, with methylene blue and electron microscopy. Three patterns of innervation were found. In the first pattern, the distal (DAFM) and proximal (PAFM) heads of the accessory flexor muscle were supplied by two axons (a thick and a thin) which travel in a private nerve along the length of the merus. This pattern was found in the crab (Cancer) and the lobster (Homarus), and conforms to the classical pattern established in the literature. In the second pattern, the nerve to the DAFM is made up of conjoined branches of the flexor and accessory flexor nerves. Consequently, the DAFM receives at least five axons in the portunid crabs, Carcinus, Callinectes, and Ovalipes, and occasionally six axons in Ovalipes. The PAFM in those portunids receives the usual two axons. In the third pattern, based on preliminary observations on the grapsid crab, Pachygrapsus, “super-innervation” of the accessory flexor muscle appears to include not only five axons to the DAFM but also at least three to the PAFM. In all species, methylene blue staining of the axon terminations revealed a regular pattern of blebs which are thought to correspond to synaptic terminals as revealed by electron microscopy.     

Fiber composition of the distal accessory flexor muscle in several decapod crustaceans

The fiber composition of the distal accessory flexor muscle (DAFM) and the branching pattern of its excitor axon were compared in several species of crabs, in the lobster and the crayfish. The muscle is composed exclusively of long sarcomere (> 6 μm) fibers and therefore of the slow type. In all the crab species, except one, there is a distal to proximal gradient of fibers with increasing sarcomere lengths; this gradient is reverse in lobsters and crayfish. A proximal to distal gradient of increasing fiber diameters occurs in the DAFM of all crab species but not in the lobster and crayfish, in which all the fibers are approximately equal in diameter. The single excitatory axon traverses the width of the DAFM and gives off primary branches on either side in the lobster and crayfish but on only one side in crabs. The hypothesis that the axonal branching pattern may govern the regional distribution of fibers with differing sarcomere lengths in proposed.     

Biomechanics of chelipeds in some decapod crustaceans

The major chelipeds of five species of decapod crustaceans were studied with reference to lever system mechanical advantage, pattern of occlusive geometry, and force/pressure developed during cheliped closure by intact animals. Every cheliped type was found to possess a linear array of two to four distinctive regions of occlusion. The factors responsible for the differences in occlusive design are discussed. It is suggested that crustacean major chelipeds must be regarded as regionally-specialized, multifunctional appendages.     

Functional cytology of the hepatopancreas of decapod crustaceans

This article reviews the morphogenesis, morphology, histology, ultrastructure, and structural–functional relationships of the hepatopancreas, the main metabolic organ of the Decapoda. The hepatopancreas develops in early larval stages from a pair of lateral lobes of the midgut anlage. In adults, it consists of hundreds of blindly ending tubules that are enveloped by a muscle net consisting of longitudinal and circular fibers. Stem cells at the distal ends of the tubules give rise to three ultrastructurally different epithelial cell types, the R-, F-, and B-cells. Histochemistry, immunohistochemistry, in situ hybridization, and monitoring of ultrastructural changes under different experimental conditions allowed the attribution of functions to these cell types. R-cells serve for the absorption and metabolization of nutrients, storage of energy reserves and minerals, synthesis of lipoproteins for export to other organs, detoxification of heavy metals, and excretion of uric acid. F-cells synthesize digestive enzymes and blood proteins involved in oxygen transport and immune defense. They also detoxify some heavy metals and probably organic xenobiotics. B-cells are assumed to produce and recycle fat emulsifiers. The hepatopancreas tubules lack nerves. The presence of scattered M-cells with putative endocrine function in the epithelium suggests that the hepatopancreas is mainly hormonally controlled. M-cells probably represent a self-perpetuating cell lineage independent from E-cells. The interstitium between the tubules contains connective tissue, arterioles, hemolymph with circulating hemocytes, and fixed phagocytes that eliminate pathogens. The hepatopancreas is histologically and ultrastructurally uniform throughout the Decapoda, despite their broad variety in body size, morphology, life style, and ecology. However, in a few cavernicolous and deep-sea shrimps parts of the hepatopancreas are transformed into large oil storing and bioluminescent compartments. Within the malacostracan crustaceans, the hepatopancreas of the Decapoda is most similar to the digestive gland of the Euphausiacea, supporting close taxonomic relationship of these two taxa.     

A review of gastric processing in decapod crustaceans

This article reviews the mechanical processes associated with digestion in decapod crustaceans. The decapod crustacean gut is essentially an internal tube that is divided into three functional areas, the foregut, midgut, and hindgut. The foregut houses the gastric mill apparatus which functions in mastication (cutting and grinding) of the ingested food. The processed food passes into the pyloric region of the foregut which controls movement of digesta into the midgut region and hepatopancreas where intracellular digestion takes place. The movements of the foregut muscles and gastric mill are controlled via nerves from the stomatogastric ganglion. Contraction rates of the gastric mill and foregut muscles can be influenced by environmental factors such as salinity, temperature, and oxygen levels. Gut contraction rates depend on the magnitude of the environmental perturbation and the physiological ability of each species. The subsequent transit of the digesta from the foregut into the midgut and through the hindgut has been followed in a wide variety of crustaceans. Transit rates are commonly used as a measure of food processing rates and are keys in understanding strategies of adaptation to trophic conditions. Transit times vary from as little as 30 min in small copepods to over 150 h in larger lobsters. Transit times can be influenced by the size and the type of the meal, the size and activity level of an animal and changes in environmental temperature, salinity and oxygen tension. Ultimately, changes in transit times influence digestive efficiency (the amount of nutrients absorbed across the gut wall). Digestive efficiencies tend to be high for carnivorous crustaceans, but somewhat lower for those that consume plant material. A slowing of the transit rate allows more time for nutrient absorption but this may be confounded by changes in the environment, which may reduce the energy available for active transport processes. Given the large number of articles already published on the stomatogastric ganglion and its control mechanisms, this area will continue to be of interest to scientists. There is also a push towards studying animals in a more natural environment or even in the field and investigation of the energetic costs of the components of digestion under varying biotic and environmental conditions will undoubtedly be an area that expands in the future.     

SEM observations on the cuticles of some decapod crustaceans

The cuticles of the crayfish Austropotamobius pallipes (Lereboullet), and the crabs Cancer pagurus L. and Carcinus maenas (L.), have been examined with the scanning electron microscope. Laminae are composed of sheets of horizontal fibres which subsequently are into the inter-laminae. The inter-laminae contain sheets of fibres which are at a slight angle from the horizontal between sucessive laminae. The disposition of the pore canals is clearly related to fibre pattern. The sinuous macrofibres described by Dennell (1973) are discrete from the pore canals.     

Aspartic proteinases in the digestive tract of marine decapod crustaceans

Decapod crustaceans synthesize highly active proteolytic enzymes in the midgut gland and release at least a part of them into the stomach where they facilitate the first step in peptide hydrolysis. The most common proteinases in the gastric fluid characterized so far are serine proteinases, that is, trypsin and chymotrypsin. These enzymes show highest activities at neutral or slightly alkaline conditions. The presence of acid proteinases, as they prevail in vertebrates, has been discussed contradictorily yet in invertebrates. In this study, we show that acid aspartic proteinases appear in the gastric fluid of several decapods. Lobsters Homarus gammarus showed the highest activity with a maximum at pH 3. These activities were almost entirely inhibited by pepstatin A, which indicates a high share of aspartic proteinases. In other species (Panulirus interruptus, Cancer pagurus, Callinectes arcuatus and Callinectes bellicosus), proteolytic activities were present at acid conditions but were distinctly lower than in H. gammarus. Zymograms at pH 3 showed in each of the studied species at least one, but mostly two-four bands of activity. The apparent molecular weight of the enzymes ranged from 17.8 to 38.6 kDa. Two distinct bands were identified which were inhibited by pepstatin A. Acid aspartic proteinases may play an important role in the process of extracellular digestion in decapod crustaceans. Activities were significantly higher in clawed lobster than in spiny lobster and three species of brachyurans. Therefore, it may be suggested that the expression of acid proteinases is favored in certain groups and reduced in others.     

Phylogeographic patterns of decapod crustaceans at the Atlantic-Mediterranean transition

Comparative multispecies studies allow contrasting the effect of past and present oceanographic processes on phylogeographic patterns. In the present study, a fragment of the COI gene was analyzed in seven decapod crustacean species from five families and with different bathymetric distributions. A total of 769 individuals were sampled along the Atlantic-Mediterranean transition area in order to test the effect of three putative barriers to gene flow: Strait of Gibraltar, Almeria-Oran Front and Ibiza Channel. A significant effect of the Strait of Gibraltar was found in the crabs Liocarcinus depurator and Macropipus tuberculatus. The Ibiza Channel had a significant effect for L. depurator. However, the Almeria-Oran front was not found to have a significant effect on any of the studied species. Higher levels of population structure were found in shallow-water species, although the number of species sampled should be increased to obtain a conclusive pattern. The haplotypes within the different species coalesced at times that could be related with past climatic events occurring before, during and after the last glacial maximum. Given the large diversity of phylogeographic patterns obtained within decapods, it is concluded that both historical and contemporary processes (marine current patterns, bathymetry and life-history traits) shape the phylogeographic patterns of these crustaceans.     

Arrays of particles in the sarcolemma of the distal accessory flexor muscle of the lobster

Summary Freeze-fracture of the distal accessory flexor muscle reveals the presence of randomly distributed arrays of P- and E-face particles. The particles are arranged in regularly spaced rows which parallel one another and, in general, the long axis of the muscle fiber. P- and E-face arrays differ in their structure and are apparently complementary. A model explaining the apparent interrelationship of the P- and E-face arrays is presented. The functional significance of the arrays is not known.We thank J. Pearce for technical assistance and Dr. R.R. Shivers, Department of Zoology, University of Western Ontario for his provision of freeze-fracture facilities. This work was supported by grants from the Natural Sciences and Engineering Council of Canada and the Muscular Dystrophy Association of Canada to C.K.G.     

Biogenic amines and DOPA in the central nervous system of decapod crustaceans

The biogenic amines serotonin (5-HT), dopamine (DA), noradrenaline (NA), octopamine (OA) and the amino acid dihydroxyphenylalanine (DOPA) were identified and measured in the brain and the eyestalks of five decapod crustacean species using high pressure liquid chromatography (HPLC) with electrochemical detection. The amounts fall within 0.01-1.1 micrograms/g or 0.17-60 pmoles, and OA is the dominating amine in most species. THe DOPA levels in many of the species varied considerably between different measurements. It is concluded that the biogenic amines and DOPA are ubiquitous in the central nervous system of decapod crustaceans and the presence of NA and DOPA increases the number of presumed neurotransmitter/modulator candidates in the crustacean nervous system.     

Intron-spanning primers for the amplification of the nuclear ANT gene in decapod crustaceans

We describe polymerase chain reaction primers that amplify the low-copy nuclear adenine nucleotide transporter gene in decapod crustaceans. These were tested on 35 species from 14 decapod families, and a single polymerase chain reaction product amplified in 32 species. Of 49 sequences generated, only two did not contain an intron, and the longest intron identified was more than 834 nucleotides in length. The amplified fragment is likely to be useful at various taxonomic levels. While the intron is suitable for phylogeographical/population genetic studies and to identify cryptic speciation, the second exon region is sufficiently long to provide signal at both the phylogeographical and phylogenetic levels.     

Involvement of the hyperglycemic neurohormone family in the control of reproduction in decapod crustaceans

Summary

In the last few years, (bio)chemical and molecular biological studies have shown that several members of the hyperglycemic hormone family are present in different molecular forms. In vivo and in vitro bioassays revealed that some of these isoforms also play a role in the control of reproduction in decapod crustaceans. This communication gives a review of the cytological aspects of the eyestalk X-organ sinus gland complex, responsible for the synthesis, storage and release of these neuropeptides, and the molecular and functional aspects of those members involved in the control of reproduction. Finally, the role of the hyperglycemic hormone family in the regulation of reproduction in the female lobster is described as an example of the (possible) interactions of the members of the hyperglycemic hormone family with other (neuro)endocrine factors in the reproductive process of crustaceans.     

Skeletal adaptations for forwards and sideways walking in three species of decapod crustaceans

Crustaceans have been successfully employed to study legged locomotion for decades. Most studies have focused on either forwards-walking macrurans, or sideways-walking brachyurans. Libinia emarginata is a Majoid crab (Brachyura) and as such belongs to the earliest group to have evolved the crab form from homoloid ancestors. Unlike most brachyurans, Libinia walks forwards 80% of the time. We employed standard anatomical techniques and motion analysis to compare the skeleton, stance, and the range of motion of the legs of Libinia to the sideways-walking green shore crab (Carcinus maenas), and to the forwards-walking crayfish (Procambarus clarkii). We found animals tended to have greater ranges of motion for joints articulating in the preferred direction of locomotion. Leg segments proximal to such joints were comparatively longer. Thorax elongation, leg length and placement at rest also reflected walking preference. Comparative studies of walking in Libinia and other brachyurans may shed light on the neuroethology of legged locomotion, and on the anatomical and physiological changes necessary for sideways-walking in crustaceans.     

Identification and cytochemical study of an extranuclear basic protein in the spermatozoa of decapod crustaceans

Extranuclear basic proteins have been detected in the capsule of the spermatozoa of three species of decapod crustaceans (Nephrops norvegicus L., Macrura; Eupagurus bernhardus L., Anomura; Carcinus maenas Penn., Brachyura). Their properties have been studied by cytochemical methods. Their position inside the capsule of the spermatozoon has been specified with the aid of the electron microscope. Present in a constant fashion in the three species cited, their relative importance is very variable. In contrast to the refringent cone of the spermatozoon of Ascaris, which contains an acid protein, ascaradine, the capsule of the spermatozoon of the three decapod crustaceans studied contains basic proteins which we propose to designate by the general term "decapodine".     

The structure and distribution of satellite cells of cardiac muscles in decapod crustaceans

Summary The structure and distribution of satellite cells of cardiac muscles were examined in twenty-one species of animals chosen from each tribe within the order Decapoda (Arthropoda, Crustacea). The satellite cells were found in all animals observed. Most of them are morphologically identical with those described in different striated muscles of other species, but some cells have unusual features. The decapod satellite cell occasionally lies right over the region corresponding to the intercalated disc between the apposed cardiac muscle cells. The cell sends cytoplasmic processes into the adjacent muscle cells, enabling the plasma membrane to make close contact with the cleft opening of the intercalated disc, and with the myofibril at the level of the Z-line. Another characteristic feature is the presence of paired cells. Such cells are clearly separated from each other over most of the contact area by the respective plasma membranes, which are smooth in appearance and devoid of specialized regions. The significance of the presence of satellite cells in decapod cardiac muscle and its possible role are discussed and compared with those described for other species.     

Comparative study of the stomatogastric system of several decapod crustacea. I. Skeleton

The skeletal structure of the stomachs of several decapod Crustacea is described in detail. The general organization of the ossicles is similar for all species and the homologies of the elements can be recognized despite large variations from group to group. The Reptantia are characterized by a complex ossicle organization while the Natantia, on the other hand, are characterized by a simple organization. The various types of ossicle organization found in the decapod stomach can be arranged in a series ranging from simple to complex. The Brachyura have the most complex ossicle system and the Penaeidea the most simplified. This graded series of complexity closely follows the evolution of the Decapoda.