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PubMed2000

Hepatopancreatic alterations in Litopenaeus vannamei (Boone, 1939) (Crustacea: Decapoda: Penaeidae) experimentally infected with a Vibrio alginolyticus strain.

As in other countries, the presence of disease has affected and limited the development of shrimp culture in Venezuela. Vibriosis is one of the most prevalent, causing high mortality not only in larval cultures but also in shrimp production. The present work shows the histological changes in hepatopancreas of Litopenaeus vannamei experimentally induced by a strain of Vibrio alginolyticus. The shrimps were infected by the immersion technique, being exposed to a concentration of 5.2 x 10(7) bacteria/ml. As soon as their behavior indicated a moribund condition, the animals were sacrificed, and their hepatopancreata were fixed and processed for histological observation. Light microscopical observations revealed loss of the acinar structure of the digestive gland and sloughing off of cellular lining because of cytolisis. The acinar cellular content was dispersed within the lumina and among the acini. Clusters of hemocytes, in the majority loaded with bacteria, were observed under the connective tissue capsule surrounding the hepatopancreatic lobes and in the hemal spaces of the connective tissue sheath surrounding the tubules.

Animals↗
PubMed2000

Ultrastructure and cytopathology of a rickettsia-like organism causing systemic infection in the redclaw crayfish, Cherax quadricarinatus (Crustacea: decapoda), in Ecuador.

A study of the ultrastructural characteristics of an intracellular bacterium infecting the redclaw crayfish, Cherax quadricarinatus, a pathogen referred to previously as a rickettsia-like organism (RLO), revealed the presence of different developmental stages. These included a rod-shaped and uniformly electron-dense elementary body (EB) and an intermediate body (IB). The length of the EB varied between 0.48 and 0.6 microm, and the diameter was 0.3 microm. The IB was 0.75 to 1.1 microm long by 0.36 to 0.44 microm in diameter. Although the EB of this bacterium has ultrastructural characteristics similar to those of Rickettsiella, no information is available regarding its genetic relationship to this genus, and the intracellular bacterium should continue to be referred to as a rickettsia-like organism. The hemocytes had different levels of infection, and the RLO proliferated inside these cells. The EB appeared to be free in the cytoplasm of infected hemocytes and other cells; however, this might be a fixation artifact. The EB was also contained in membrane-bound vacuoles along with the IB. RLO colonies were observed inside small granular cells. No large granular cells were observed in the sections examined; therefore, no data were obtained regarding infection of this type of hemocyte. The fixed phagocytes on the external side of the terminal hepatic arterioles had an activated interrupted layer containing RLO bacteria. Stem cells in the hematopoietic tissue were also infected, and some cells were apparently being released into circulation.

Animals↗
PubMed1997

The polyhedra of the occluded baculoviruses of marine decapod crustacea: A unique structure, crystal organization, and proposed model

The baculoviruses of marine penaeid shrimp, PmSNPV and PvSNPV (MBV type and BP type, respectively), have distinctly different occlusion bodies (OBs) from those of the insect baculoviruses. In contrast to insect baculovirus, the penaeid baculovirus OB is unenveloped and formed by large subunits (SuOBs), as observed by electron microscopy after negative staining. The polyhedrin subunits measure 17 to 23 nm in diameter and appear icosahedral, resembling full and empty viral particles. Although these SuOBs look similar in morphometrics to shrimp parvoviruses, their density, polypeptide composition, and UV spectra are more characteristic of proteins than nucleoproteins. Common to the two shrimp baculovirus OBs that were investigated is the aggregation of three icosahedral SuOBs into a triplet. The observed difference in their crystalline structure is directly related to the way in which triplets attach to each other to form the OB. In the BP-type OB, the triplets form alternating parallel rows in all three dimensions. On the other hand, in the MBV-type OB, four triplets form a hollow sphere which we call a "rosette," the building blocks of the MBV-type OB. We assembled models for the penaeid baculovirus OB as an alternative to those hypothesized for insect baculovirus OBs. Copyright 1997 Academic Press. Copyright 1997 Academic Press

Journal Article↗
PubMed1996

Phylogenetics and evolution of the Daphnia longispina group (Crustacea) based on 12S rDNA sequence and allozyme variation.

Although members of the crustacean genus Daphnia have been the target of much research, there is little understanding of the group's evolutionary history. We addressed this gap by inferring a phylogeny for one of the major species groups (longispina) using nucleotide sequence variation of a 525-bp segment of the mitochondrial 12S rDNA and allozyme variation at 21 loci. We identified the major lineages and their relationships, assessed the phylogenetic utility of the few morphological characters in the group, and examined Daphnia phylogeography. Nuclear and mtDNA phylogenies were generally concordant in recognizing the same four species complexes. An exception was the position of Daphnia galeata mendotae. The allozyme tree paired this species with the Daphnia rosea lineage, whereas the mtDNA trees grouped D. g. mendotae with Daphnia galeata galeata. This discordance was consistent with the reticulate evolution of nuclear genes supporting the hypothesis that D. g. mendotae represents a case of homoploid hybrid speciation. Striking morphological stasis in the longispina group was evidenced by its very limited morphological divergence over an estimated 100 MY, and by the unusual transitional saturation of the conservative 12S rRNA gene within a species group. Phylogenetic inference also provided evidence that similarities in cephalic crest shape likely resulted from convergent or parallel evolution among species. Endemism at the continental level was indicated for previously cosmopolitan species, but the estimated times of these divisions were inconsistent with vicariance events suggesting recent dispersal among continents. A significant role for divergent selection in new habitats during speciation was suggested by the neighboringly sympatric distributions of four sister species pairs over broad geographic areas.

Alleles↗
PubMed1999

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.

Animals↗
PubMed2000

Molecular phylogeny, taxonomy, and evolution of nonmarine lineages within the American grapsoid crabs (Crustacea: brachyura).

Grapsoid crabs are best known from the marine intertidal and supratidal. However, some species also inhabit shallow subtidal and freshwater habitats. In the tropics and subtropics, their distribution even includes mountain streams and tree tops. At present, the Grapsoidea consists of the families Grapsidae, Gecarcinidae, and Mictyridae, the first being subdivided into four subfamilies (Grapsinae, Plagusiinae, Sesarminae, and Varuninae). To help resolve phylogenetic relationships among these highly adaptive crabs, portions of the mitochondrial genome corresponding to the 16S rRNA gene were sequenced for all grapsoid genera occurring in America. The resulting phylogeny confirms most of the present grapsid subfamilies but suggests reclassification of some of the genera and recognition of new taxonomic units. The two American gecarcinid genera might not represent a sister group to the Grapsidae but rather appear to have evolved within the latter. Colonization of inland habitats evolved in several lineages of the grapsoids, resulting in various forms of nonmarine life and different degrees of independence from the sea.

Animals↗
PubMed1976

The fine structure of the carapace integument of Daphnia magna Straus (Crustacea Branchiopoda).

The structure of the two integumental layers comprising the carapace of female D. magna was examined at several points through the molt cycle. The epicuticle and procuticle are simple in organisation; pore canalsare absent but intracuticular fibres are present, forming complexes with invaginations of the epidermal plasma membrane similar to such complexes described in the literature for othe arthropods. The epidermis consist almost entirely of cuticle-secreting cells. Secretion of the new cuticle begins when 50-67% of the instar has elapsed by which time the epidermal cells have increased in height and their nuclei have become more rounded. However, other presumed secretory phenomena observed viz. the formation of dense core vesicles by Golgi bodies, and the occurrence of these and coated vesicles near the apical plasma membrane are not restricted to any particular period during the molt cycle. This suggests that the mechanisms of cuticle secretion do not undergo marked changes in activity as they do in decapods; presumably this relative continunity is related to the much shorter molt cycle of cladocerans.

Animals↗
PubMed1982

The structure of the a hair mechanoreceptor in the antennule of crayfish (Crustacea).

In this study we examine the fine structure of mechanosensory hairs in the antennule of crayfish. The sensory hair is a stiff shaft with feather-like filaments. The hair's base is a large expansion of membrane which allows the hair shaft to deflect. The sensory transducing elements are located far from the hair, but are coupled mechanically with the hair shaft by a fine extracellular chorda. The sensory element is a type of scolopidium which consists of a scolopale cell and three sensory cells with a 9 + 0 type ciliary process. This type of scolopidium is characteristic of the chordotonal organ that has no cuticular structure on the surface of the exoskeleton. In this crustacean hair receptor, the deflection on the cuticular hair is transmitted through the chorda to the scolopidium which is a tension-sensitive transducer. The present study reveals that the mechanosensory hair of decapod crustaceans is a chordotonal organ accompanied by a cuticular hair structure. We also discuss comparative aspects of cuticular and subcuticular chordotonal organs in arthropods.

Animals↗
PubMed1983

The fine structure of the gill epithelium of a fresh-water flea, Daphnia magna (Crustacea: Phyllopoda) and changes associated with acclimation to various salinities. I. Normal fine structure.

Two kinds of epithelial cells, dark and light types, are alternately arranged in the gill of Daphnia magna. The dark cell has numerous mitochondria and an elaborate tubular system containing two kinds of cytoplasmic tubules, small about 70 nm in diameter, and large about 130 nm in diameter. The former occur in bundles and seem to be smooth-surfaced endoplasmic reticulum. The latter, lined with a ridged surface coat and frequently open at the lateral and basal cell membrane, are regarded as extensions of the cell membrane. The atypical cell membrane of the dark cell is modified by repeated subunits of a cytoplasmic coat on the inner leaflet of the unit membrane. The light cell exhibits a high degree of basal infoldings of the cell membrane, which represent a magnification of the surface area of the cell. Large mitochondria between the infoldings often come into intimate association with the infolded cell membrane to form a regular array of parallel mitochondria interposed with the double cell membranes. The results suggest that at least the dark epithelial cells play an important role in the osmoregulation of this animal.

Animals↗
PubMed1976

On the fine structure of the regressing ecdysial glands of carcinus maenas L. (Crustacea Decapoda) parasitized by Sacculina carcini Thompson.

The ecdysial glands (Y organs) of the crab Carcinus maenas regress in the presence of an external parasite, Sacculina carcini. This regression is more or less severe and may lead to complete autolysis. Three gradual stages in this involutionary process are described. In stage I, the gland cells are nearly normal. Nuclei and cytoplasmic organelles remain unchanged, but large vacuoles begin to appear. Stage II corresponds to more or less drastic nuclear pyknosis and cytoplasmic alterations. Myelin figures are large and numerous. Lysosomes and autophagic vacuoles with phosphatase activity are abundant. However, the general cellular architecture remains preserved. Stage III corresponds to irreversible cytolysis; nuclear envelopes and plasma membranes have disappeared. What remains is an accumulation of cellular debris becoming engulfed by circulating hemocytes. Not all of the gland cells of any given Y organ show the same degree of regression; degeneration is asynchronous. Structures seemingly corresponding to absorptive roots of the parasite are seen. Their lumen is coated with microvilli. The putative direct and indirect influences of the rhizocephalan parasite on its host are discussed. Our results on regressing Y organs of parasitized crabs are compared with those on regressing ecdysial glands of insects.

Animals↗
PubMed1978

Neuronal connectivity patterns in the compound eyes of Artemia salina and Daphnia magna (Crustacea: Branchiopoda).

The neuronal types and patterns in the visual system of the species Artemia salina and Daphina magna have been studied with the Golgi method and electron microscopy. The lamina contains five classes of neurons: photoreceptor axons, monopolar, centrifugal, tangential and amacrine neurons. The terminals of the receptor axons are distributed in two (A. salina) or three (D. magna) layers. The dilated terminals have an extensive and wide array of fine branches. One axon from each ommatidium bypasses the lamina and terminates in the medula in A. salina. A. salina has four types of monopolar neurons, two of which are stratified, whereas in D. magna only two types are found, one of which is bistratified. Tangential T-neurons connect the lamina with the protocerebrum. D. magna has in addition one tangential T-neuron connecting both the lamina and the medulla with the protocerebrum. In both species monopolar-type centrifugal neurons connect the medulla and the lamina, whereas that of A. salina has a wide laminar distribution. Both species also have amacrine cells in the lamina. The medulla contains, besides those shared with the lamina, transmedullary neurons (two types in A. salina), amacrine cells and neurons originating in the protocerebrum. "Cartridge"-type synaptic compartments are lacking in the investigated species, although a periodic arrangement is discernible in the distal portion of the lamina of A. salina. The receptors from three types of specialized contacts in Artemia, one of which involves a dyad. D. magna has only one-to-one synapses. Neurosecretory fibres are absent in A. salina.

Animals↗
PubMed1975

The membrane systems of the cardiac muscle cell of Munida tenuimana G. O. Sars (Crustacea, Decapoda).

The membrane systems of the cardiac muscle cell of Munida tenuimana G. O. Sars are described. The sarcolemma invaginates at the Z level, forming tubules. Narrow tubules branch off in a longitudinal direction from these transverse and radially arranged tubules, forming a narrow transverse collar at the H level where dyadic and triadic junctions are formed with the sarcoplasmic reticulum.

Actins↗
PubMed1984

Are the funnel-canal organs the 'campaniform sensilla' of the shore crab, Carcinus maenas (Decapoda, Crustacea)? II. Ultrastructure.

The funnel-canal organs on the dactyls of the shore crab, Carcinus maenas, are innervated by 3-24 sensory cells with unbranched dendrites, which attain a length of 500-1400 micron. The outer dendritic segments are enclosed in a dendritic sheath and pass through the cuticle within a canal. Two dendrite types can be distinguished according to ultrastructural criteria: Type I has a long ciliary segment, A-tubules with an osmiophilic core and arms, and a thick ciliary rootlet. Type II possesses only a short ciliary segment and a thin ciliary rootlet. Each funnel-canal organ contains two type-I dendrites. Their ciliary bases appear a few micron distal to those of the type-II dendrites (1 to 22 in number). Two inner and two to eight outer enveloping cells belong to a sensillum. The innermost enveloping cell contains a large scolopale. In the second enveloping cell single scolopale rods are present. Thus, the funnel-canal organs are characterized by structural features typical for mechanosensitive scolopidia, on the one hand, and for chemoreceptors, on the other. Therefore, the funnel-canal organs are very likely bimodal sensilla (contact chemoreceptors). A comparison with other arthropod sensilla shows that cuticular mechanoreceptors of aquatic crustaceans generally exhibit a 'scolopidial' organization.

Animals↗
PubMed1990

UV photoreceptors in the compound eye of Daphnia magna (Crustacea, Branchiopoda). A fourth spectral class in single ommatidia.

The spectral sensitivities of individually stimulated ommatidia in the compound eye of Daphnia magna were measured using a fast spectral scan voltage-clamp technique with extracellular recording. Chromatic adaptation was used to reveal the contributions of individual spectral classes of photoreceptors to the ommatidial sensitivity. Ommatidia in the dorsal and ventral regions of the compound eye were tested. Four spectral classes of photoreceptors were found in each ommatidium, among them a previously undetected class with peak sensitivity in the ultraviolet. The wavelengths of peak sensitivity were at 348, 434, 525, and 608 nm for the dorsal ommatidia. The three longer wavelength classes agreed well with those found previously by intracellular recording (Schehr 1984). Only small differences in wavelength and magnitude of peak sensitivity were found between the four classes in the dorsal versus ventral ommatidia.

Animals↗