Ontogeny of Osmoregulation in Crustaceans: The Embryonic Phase

Following a brief overview of the patterns of ontogeny of osmoregulationin postembryonic stages, this review concentrates on the ontogenyof osmoregulation during the embryonic development of crustaceans,particularly in those species living under variable or extremesalinity conditions and whose hatchlings osmoregulate at hatch.Two situations are considered, internal development of the embryosin closed incubating, brood or marsupial pouches, and externaldevelopment in eggs exposed to the external medium. In bothcases, embryos are osmoprotected from the external salinitylevel and variation, either by the female pouches or by theegg envelopes. The mechanisms of osmoprotection are discussed.During embryonic life, temporary or definitive osmoregulatoryorgans develop, with ion transporting cells and enzymes suchas Na⁺-K⁺ ATPase, permitting the embryos and then the hatchlingsto osmoregulate and tolerate the external salinity.     

Bergmann's Principle and Deep-Water Gigantism in Marine Crustaceans

We present a review of the Bergmann's principle and deep-water gigantism in marine crustaceans. An increase in the geographic latitude and depth of crustaceans habitat (correlating mainly with lower temperatures) leads to an increased cell size, life span of the animal, and, as a result, an increase in the body size. Since Bergmann's principle and deep-water gigantism appear to be based on the same biological mechanisms, we propose a unified principle, according to which the size of the crustacean's body increases along the temperature gradient.     

Chitin and Chitosan: Functional Biopolymers from Marine Crustaceans

Chitin and chitosan, typical marine polysaccharides as well as abundant biomass resources, are attracting a great deal of attention because of their distinctive biological and physicochemical characteristics. To fully explore the high potential of these specialty biopolymers, basic and application researches are being made extensively. This review deals with the fundamental aspects of chitin and chitosan such as the preparation of chitin and chitosan, crystallography, extent of N-acetylation, and some properties. Recent progress of their chemistry is then discussed, focusing on elemental modification reactions including acylation, alkylation, Schiff base formation and reductive alkylation, carboxyalkylation, phthaloylation, silylation, tosylation, quaternary salt formation, and sulfation and thiolation.     

Latitudinal Variations in Body Size and Species Diversity in Marine Decapod Crustaceans of the Continental Shelf

The number of species of caridean, brachyuran and anomuran decapods increases from high to low latitudes in both hemispheres. This is shown to be due mainly to changes in the abundance of small species. Possible explanations for these variations in abundance are discussed. The other infraorders of decapods are confined to mid and low latitudes.     

Recognition of Non-self in Crustaceans

This paper reviews the current concepts of recognition of non-selfin crustaceans and relates these concepts to recognition inthe invertebrates in general. It focuses primarily on a decapodcrustacean, the blue crab(callinectes sapidus)and on resultsusing this animal as a model to study the clearance of virusesand xenogeneic proteins. Clearance studies indicate that bluecrabs possess a quasi-specific recognition system in the normalor "non-immunized"state. This system is capable of rapidly clearingforeign proteins and certain viruses from the circulation, andresults in concentration of such proteins into the gills andviruses into the hepatopancreas or gills. Although humoral factorswhich bind foreign proteins or neutralize viruses have beenisolated, transfusion exchange experiments involving depletionof circulating cells and/or humoral factors indicate that theblue crab does not require circulating hemocytes or humoralfactors for clearance of foreign proteins. These results suggestthat a population of fixed cells, possibly those in the gills,may be the critical component for recognition of foreign proteinsby normal crabs.     

Immunity in Decapod Crustaceans

Immunity in the decapod crustaceans is surveyed. Types of immuneresponses include encapsulation, phagocytosis with or withoutthe aid of serum factors, bactericidins active with or withoutthe aid of hemocyte factors, hemagglutinins, hemolysins, agglutinins,and precipitins. Immunity to gaffkemia in Panulirus interruptusis also discussed.     

Occurrence of Hemocyanin in Ostracod Crustaceans

Hemocyanin is a copper-containing protein that transports O₂ in the hemolymph of many arthropod species. Within the crustaceans, hemocyanin appeared to be restricted to Malacostraca but has recently been identified in Remipedia. Here, we report the occurrence of hemocyanin in ostracods, indicating that this respiratory protein is more widespread within crustaceans than previously thought. By analyses of expressed sequence tags and by RT-PCR, we obtained four full length and nine partial hemocyanin sequences from six of ten investigated ostracod species. Hemocyanin was identified in Myodocopida (Actinoseta jonesi, Cypridininae sp., Euphilomedes morini, Skogsbergia lerneri, Vargula tsujii) and Platycopida (Cytherelloidea californica) but not in Podocopida. We found no evidence for the presence of hemoglobin in any of these ostracod species. Like in other arthropods, we identified multiple hemocyanin subunits (up to six) to occur in a single ostracod species. Bayesian phylogenetic analyses showed that ostracod hemocyanin subunit diversity evolved independently from that of other crustaceans. Ostracod hemocyanin subunits were found paraphyletic, with myodocopid and platycopid subunits forming distinct clades within those of the crustaceans. This pattern suggests that ostracod hemocyanins originated from distinct subunits in the pancrustacean stemline.     

Aspects of Lipid Metabolism in Crustaceans

Lipid is the predominant organic reserve of many crustaceansand is important in the metabolism of many of these animals.Ingested lipid is digested by gastric lipase and apparentlyabsorbed into depot-lipid as rß-monoglycerides. Thevariation in the content and composition of the depot-lipidis a function of both the external environment and internalcontrol systems. Evidence suggests that lipids from marine organismscontain more long-chain polyunsaturated fatty acids than doesthe lipid of fresh water organisms which in turn have a highproportion of C₁₆ and C₁₈ fatty acids. The fatty-acid compositionof the sub-tropical land crab,Gecarcinns lateralis, resemblesthat of the fresh-water crustaceans. In addition, our studiesindicate that aspects of lipid metabolism may be under endocrinecontrol. The induction of premolt by destalking markedly increasesthe synthesis of lipid from metabolic precursors and its subsequentincorporation into the depot-lipid of the hepatopancreas. Inthe late premolt stages there is a decrease in the lipid contentof the hepatopancreas. This occurs as the lipid is mobilizedfrom the hepatopancreas to meet the energy demands of all thoseprocesses resulting in ecdysis. This sinusoidal variation inthe lipid metabolism of the hepatopancreas is influenced byan eyestalk factor (s).     

The Application of DNA Barcodes for the Identification of Marine Crustaceans from the North Sea and Adjacent Regions

During the last years DNA barcoding has become a popular method of choice for molecular specimen identification. Here we present a comprehensive DNA barcode library of various crustacean taxa found in the North Sea, one of the most extensively studied marine regions of the world. Our data set includes 1,332 barcodes covering 205 species, including taxa of the Amphipoda, Copepoda, Decapoda, Isopoda, Thecostraca, and others. This dataset represents the most extensive DNA barcode library of the Crustacea in terms of species number to date. By using the Barcode of Life Data Systems (BOLD), unique BINs were identified for 198 (96.6%) of the analyzed species. Six species were characterized by two BINs (2.9%), and three BINs were found for the amphipod species Gammarus salinus Spooner, 1947 (0.4%). Intraspecific distances with values higher than 2.2% were revealed for 13 species (6.3%). Exceptionally high distances of up to 14.87% between two distinct but monophyletic clusters were found for the parasitic copepod Caligus elongatus Nordmann, 1832, supporting the results of previous studies that indicated the existence of an overlooked sea louse species. In contrast to these high distances, haplotype-sharing was observed for two decapod spider crab species, Macropodia parva Van Noort & Adema, 1985 and Macropodia rostrata (Linnaeus, 1761), underlining the need for a taxonomic revision of both species. Summarizing the results, our study confirms the application of DNA barcodes as highly effective identification system for the analyzed marine crustaceans of the North Sea and represents an important milestone for modern biodiversity assessment studies using barcode sequences.     

Neuroendocrine Correlates of Circadian Rhythmicity in Crustaceans

The secretion of neurohormones from the crustacean X-organ –sinus gland system is controlled by environmental influences,light being the most conspicuous. Two sets of photoreceptorsappear to mediate the influence of light on neurosecretion basedon intracellular recordings from X-organ neurons and estimationsof hormone release. Extra-retinal photoreceptors can initiateneurohormonal release from the eyestalk. Neurosecretory activity is also influenced by putative neurotransmitters.GABA is found in high concentrations in the medulla temninalisof the eyestalk and is released by stimulation, in a calcium-dependentmanner. Diurnal variations occur in the amounts of eyestalk neurohormones,either those present in the eyestalk or released by electricalstimulation of the isolated sinus gland. Rhythm phases varyfrom one hormone to another. Neurohormones secreted in the eyestalkare also found in other regions of the central nervous system.Rhythms of neurosecretion are present both in the secretionin the isolated eyestalk and in eyestalkless animals, thus indicatingthat rhythmicity is a distributed property of the neurosecretorysystem.     

The Circadian System of Crustaceans

Crustaceans exhibit a variety of overt circadian rhythms. Observations on intact animals suggest the existence of more than one circadian pacemaker in the nervous system. Ablation experiments so far have been inconclusive in pinpointing the location of putative pacemakers. However, various structures, most notably the optic peduncle, have been shown to sustain circadian rhythmicity in vitro. Retinal sensitivity and neurosecretory activity display circadian rhythms in the isolated optic peduncle, but they are also responsive to synchronizing influences from other regions of the central nervous system, most notably the supra-esophageal ganglion. A model based on a number of circadian pacemakers distributed in the central nervous system best fits the experimental results at present. Coupling of rhythmicity between independent circadian pacemakers is likely to occur, and a neuroendocrine stage of integration has been proposed for several rhythms. Various entraining agents have been identified, and more than one may play a part in the synchronization of a given rhythm.     

Cuticular Proteins in Insects and Crustaceans

Comparisons between crustacean and insect cuticles are hamperedby the paucity of cuticular protein sequences for the former.Sufficient complete sequences are available for insect cuticularproteins to allow recognition of conserved motifs and relationshipsamong proteins that reflect the type of cuticle from which theyhave been extracted. All five sequences from an arachnid andtwo of 14 from crustaceans have a motif found in the largestgroup of insect cuticular proteins. Numerous insights have beengained from studying insect cuticular proteins and their genes.These insights have been summarized in hopes of encouraginginterest in building on the foundations laid by Dorothy Skinnerwith the exoskeleton of Gecarcinus.     

Co-evolution Between Fishes and Crustaceans

In aquatic ecosystems fishes are, in general, the most important predators of crustaceans. This must not have been so at the beginning of the Mesozoic. Evolution of aquatic vertebrates led from heavy, benthic, microphagous animals to buoyant, agile, omnivorous ones. Key events of this evolution took place in fresh water, while most crustacean groups probably evolved in marine habitats. It is pointed out that until early Jurassic times the caridoid escape reaction obviously ensured the survival of eucarid species, while the later radiation suggests that selection favoured well-calcified and short-tailed species. It is suspected that the radiation of the marine Teleostei is a main cause of this evolution. This hypothesis is in accordance with the occurrence of the most archaic crustacean relict species in fish-free habitats.     

Standard Metabolism and Macrotaxonomy of Crustaceans

The influence of temperature and other environmental factors on the rate of oxygen consumption has been studied in adult crustaceans. The allometric relationship between respiration and body weight was calculated for 15 crustacean orders on the basis of published data on the standard metabolic rate and body weight in 225 crustacean species. The macrotaxonomy of the studied crustacean orders was proposed on the basis of the obtained values of coefficient a from the allometric relationship.     

To the Question of Eyes in Primitive Crustaceans

Based on a review of studies of functional and comparative anatomy of crustacean eyes, a hypothesis is formed on eyes in primitive crustaceans. It is suggested that they were similar to present-day frontal eyes of the malacostracan type. Neuronal architecture suggests that the development to apposition compound eye followed two main routes, one seen in malacostracans and the other in non-malacostracans. Within the two subgroups different and separate lines have been followed to form specialized apposition types and, within the Malacostraca, superposition eyes as pointed out by Nilsson (Nilsson, D. E. 1989. Facets of vision, pp. 30–73).     

Endocrine Regulation of Lipid Synthesis in Decapod Crustaceans

The legulation of lipid synthesis in the hepatopancreas of thecrab Pachygrapsus crassipes and the crayfish Procambarus sp.was investigated. Although deatalking induces an increase inthe rate of ¹⁴C-1-acetate incorporation into lipid, injectionsof crustecdysone into intermolt animals fail to elicit a similarresponse. In addition, the increased rate of lipid synthesisinduced by destalking is unaffected by removal of the Y-organ.It would appear then that the increase in lipid synthesis characteristicof early premolt is not controlled by either crustecdysone orthe Y-organ. It is suggested that formation of acetyl-CoA byany one of a number of possible mechanisms may bethe mannerin which the increase in fatty acid synthesis is effected duringpremolt.     

Hemolymph Proteins and Molting in Crustaceans and Insects

The exoskeleton of crustaceans and insects is formed by cellsof the hypodermis, but several hemolymph proteins contributeto the synthesis of the new exoskeleton. These hemolymph proteinsshare a surprising degree of sequence similarity and are membersof the hemocyanin gene family. Copper-containing prophenoloxidasesof crustaceans and insects are directly involved in cross-linkingand hardening of the exoskeleton during molting and repair.Crustacean cryptocyanin and insect hexamerins lack copper andhave probably evolved from a copper-free product of an earlyhemocyanin gene duplication. These proteins have been implicatedin transport of hormones and phenols, and may be used directlyas structural components of the new exoskeleton. They are synthesizedelsewhere in the body, transported in the hemolymph, and probablytaken up by the hypodermis via specific receptors. Hemocyaninshave some residual phenoloxidase activity, in addition to theirprimary role of supplying oxygen to the metabolizing tissues.Thus multiple members of the hemocyanin gene family play vitalroles during molting, and a molecular phytogeny of these proteinswill contribute to our understanding of the evolution of formand function of these molecules from oxygen transport to molt-relatedactivities. Further studies on the expression of prophenoloxidase,cryptocyanin, hexamerins and hemocyanin, potential marker proteins,may extend our understanding of the relationship between othermolting animals in the proposed clade, Ecdysozoa.