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At least 217 records · Page 12Linked to original sources
PubMed1975

Studies on the fine structure of the cuticle of Porcellidium, crustacea copepoda.

Two species of Porcellidium have been studied by scanning and transmission electron microscopy: P. viride from Banyuls-sur-mer, Mediterranian Sea and P. fimbriatum from Roscoff, English Channel. Both species live on green Algae of the genus Ulva. We confirmed previous descriptions of the cuticular ultrastructure in the main groups of Copepods. Four new characteristics however were shown to occur in the backcuticle of Porcellidium: 1. The presence of a system of highly differentiated external microvilli showing electron dense basal portions and less electron dense tips, from which thin filaments project towards a large population of Bacteria associated with the Copepod. 2. The surface of the cuticle resembles a lunar landscape with craters. The sheet of microvilli closely follows the contour of the cuticle. 3. The presence of branched cytoplasmic canals with swollen extremities (beneath the epicuticle) extending from the epidermal cells. 4. Systems of vesicles lying between the bases of the microvilli and the expansions (ampullae) at the tip of the cytoplasmic canals. The association of Bacteria with the cuticle is constant and many of these are apparently undergoing cytolysis; The system of microvilli and of cytoplasmic canals are apparently related to the presence of the bacterial microflora.

Animals↗
PubMed1977

The connections of the sensory organ of Bellonci with the brain in Isopoda (crustacea).

The peduncle linking the organ of Bellonci with the brain was examined in Sphaeroma serratum and Anilocra frontalis. This peduncle, in its extension to the brain, becomes a nerve-like tract with bundles of pedicles originating from the sensory cell bodies located in the organ of Bellonci. It ends at the level of the medulla interna in an alveolar region resulting from the swelling of the sensory pedicle terminations. At this level three types of connections have been observed. The first is characterized by afferent synapses to the brain with, in the sensory pedicle endings, structures similar to the presynaptic ribbons noted by some authors in photoreceptors of arthropods. The two other types include nerve fibres originating from the brain, one with small electron lucent vesicles, a second displaying larger vesicles with a core of medium density. These fibres form efferent synapses to the organ of Bellonci. The sensory differentiation of the organ of Bellonci in Isopoda is confirmed but its true role is not specified.

Animals↗
PubMed1977

The membrane systems of the cardiac muscle cell of Meganychtiphanes norvegica (m. sars), euphauciacea, crustacea.

The membrane systems of cardiac muscle cells of the euphausiacean Meganychtiphanes norvegica are described. Transverse tubules are found both at the Z-band level (TZ-tubules) and at the H-band level (Th-tubules). Within the sarcomere narrow longitudinal tubules branch off from the TZ-tubules. At the H-band level these tubules expand forming flattened cisternae in dyadic and triadic couplings with the sarcoplasmic reticulum (SR). Adjacent myofibrils are separated by a well developed SR. Modifications of the SR are seen at the H-band level where junctional cisternae are formed.

Animals↗
PubMed1976

The membrane systems of the cardiac muscle cell of Tmetonyx cicada O. Fabricius (Crustacea, Amphipoda).

The membrane systems of the cardiac muscle cell of the amphipod Tmetonyx cicada (O. Fabricus) are described. The sarcolemma invaginates and forms a transverse network of tubules at the level of the Z band. Narrow longitudinal tubules branch from the network and connect to another transverse network of tubules at the H band level, where dyadic and triadic junctions are formed with the sarcoplasmic reticulum. Adjacent myofibrils are normally separated by a well developed double layer of the sarcoplasmic reticulum. In areas where the myofibrils closely approach the outer sarcolemma, peripheral couplings have been found at the level of the H band.

Animals↗
PubMed1977

The membrane systems of the cardiac muscle cell of Euchaeta norvegica Boeck (crustacea, copepoda).

The membrane systems of the cardiac muscle cell of the copepod Euchaeta norvegica Boeck are described. The heart wall, which is between 0.12 and 1.36 micrometer thick, consists of an epicardium and a single layer of muscle cells. Invaginations of the sarcolemma forming transverse tubules have been found at all levels of the sarcomere with the exception of the H-band level. The longitudinal tubules of the same system are closely associated with the sarcoplasmic reticulum to form interior couplings at the A-I level of the sarcomere. Triadic couplings at the Z band level were not seen in E. norvegica, but peripheral couplings were demonstrated. Nex-uses were found in the intercalated discs.

Animals↗
PubMed1977

The fine structure of the compound eye of Squilla mantis (Crustacea, Stomatopoda).

The fine structure of the compound eye of adult specimens of Squilla mantis was investigated. The eye consists of about 3600-3700 ommatidia, each containing a dioptric apparatus formed by a lamellated corneal lens and a eucone-type crystalline cone. Each of the four cone cells give rise to a cylindrical process (crystalline thread) inserted between the retinula cells and extending down to the basement membrane. Two distal pigment cells completely encompass the distal part of the crystalline cone, becoming progressively smaller and forming roundish processes. At the level of the tip of the crystalline cone they split off into small pigment-containing processes, and a central process leads down to the basement membrane. About 12-16 proximal pigment cells surround the ommatidium and extend from the tip of the crystalline cone to the basement membrane. In addition to the two types of pigment cell, three other types of pigment-containing cells were identified, one of which possibly contains - on the basis of their ultrastructure - crystals of the respiratory pigment hemocyanin. The two other pigments are found respectively on the surface of the retina (green pigment) and beneath the surface and in the intraommatidial space (white pigment). The distal part of each ommatidium consists of retinula cells of about equal size. Further proximal an 8th small retinula cell is encountered. The fused, centrally located rhabdom, is built up of the microvilli (rhabdomeres) of the 7 large retinula cells, the 8th has no microvilli. The structure of the ommatidia was also examined in relation to light-dark adapted conditions (LA-DA). In DA the crystalline cone shortens and the rhabdom becomes longer by an approximately corresponding amount and the pigments of the distal pigment cells expand more distally. The number and type of special cytoplasmic inclusions, as well as the shape and size of the so-called perirhabdomal vacuoles, seems not to be changed by light or dark-adaptation. In the 7 large retinula cells, an unusual migration of pigment granules occurs under DA conditions (the 8th does not contain pigment granules), In DA, many of granules which are distributed around the rhabdom in LA, line up in rows, like strings of pearls, along the rhabdom, forming a dense pigment coat around it. The findings are compared with those of related studies and their functional implications for the vision of Squilla are discussed.

Animals↗
PubMed1980

Evidence for hemocyanin formation in the compound eye of Squilla mantis (Crustacea, Stomatopoda).

In the retina and in the subretinal space of the compound eye of Squilla mantis a special kind of pigment cell is present. The crystalline inclusions of this cell have been identified as hemocyanin, as determined (i) by the dimensional congruence of the crystalline substructure with the dimensions of isolated, purified hemocyanin, and (ii) by the immunofluorescence reaction using anti-hemicyanin antibodies. The ultrastructure of these cells, their location and the presence of crystalline bodies in their cytoplasm suggest that they are sites of hemocyanin synthesis and homologous to the cyanocytes or cyanoblasts of Limulus.

Animals↗
PubMed1979

Ultrastructural development of the neurohemal organ joined to the ecdysial gland after imaginal moulting in the male isopod Sphaeroma serratum Fab. (Crustacea Flabellifera).

The present ultrastructural study deals with the lateral cephalic nerve plexus of Sphaeroma serratum, a neurohemal organ joined to the Y organ (ecdysial gland). This plexus acts as a storage centre for neurosecretory products from two sources: the two autochtonous cells (plexus cells) within the plexus itself, and the neurosecretory cells in various parts of the central nervous system, particulary the "mandibular ganglion" (A-cells). In prepuberal animals, plexus cells and subesophageal A-cells produce neurosecretory granules of two types measuring 1550 +/- 50 A and 1570 +/- 40 A respectively. Five categories of axon terminals were distinguished in the plexus. The granules found in two of these terminal types are believed to come from the plexus cells and from the "mandibular ganglion" A-cells. Cessation of production of neurosee plexus with concomitant depletion and disappearance of different granule categories. The first axon terminals affected by this process are the two categories containing granules originating in the plexus and "mandibular ganglion" A-cells. Degeneration of the ecdysial gland in male Sphaeroma serratum might be connected with the cessation of granule formation in these two types of cell.

Animals↗
PubMed1980

Heart ultrastructure in Lepidurus arcticus Pallas (Crustacea, Branchiopoda, Notostraca).

The heart of Lepidurus arcticus consists of an epicardium and a single layer of strongly polarized myocardial cells, 10-50 micron thick, with the myofibrillar part facing the epicardium. The Z-bands are diffuse and some Z-material forms attachment plaques. Relaxed sarcomeres show a hexagonal arrangement of thick filaments and 6 thin filaments in orbit, but filaments often diverge in their orientation. The sarcolemma invaginates from both the epicardial and the endocardial side of the cell, forming clefts and T-tubules. The sarcoplasmic reticulum is loosely reticular, cisternae associate with sarcolemma to form large and typical peripheral and interior couplings. The latter are of the "button-to-button" type and they tend to be located at the A-I level.

Animals↗
PubMed1979

Ultrastructure of the Y-organ of Astacus astacus (L.) (Crustacea) in relation to the moult cycle.

The electron microscopical investigation of Y-organs of Astacus astacus revealed that during intermoult (stage C) the cytoplasm is poorly developed and that it increases at premoult (stage D). It then shows the typical signs of steroid production, namely agranular endoplasmic reticulum and mitochondria of the tubular type. Furthermore, a larger type of mitochondria with a regular pattern of internal structure is described.

Animals↗
PubMed1981

The ultrastructure of the heart of Oniscus asellus L. and Asellus aquaticus L (Crustacea, Isopoda).

The endocardium of Oniscus asellus L. and Asellus aquaticus L. consists of lipid cells. The epicardium consists of a layer of cells with a vesiculated cytoplasm covered by a thick extracellular fibrous sheet. The myocardium is a single layer of cells, the sarcolemma invaginates at Z disc level forming transverse tubules, and longitudinal tubules branch off from these. At the A-I level longitudinal tubules from transverse systems, which form couplings with the sarcoplasmic reticulum. The sarcoplasmic reticulum appears as perforated sheets enveloping the myofibrils. Two types of nerve terminal are found: one is embedded in a myocardial cell process, the other lies in a myocardial cell depression. They contain clear and dense-cored synaptic vesicles.

Animals↗
PubMed1979

Ultrastructural observations on the oogenesis of Triops cancriformis (Crustacea, Notostraca). II. Early developmental states of the oocyte.

The first stages of the oogenesis of Triops cancriformis have been studied. At the outset the oocyte is smaller than the nurse cells. Meiosis begins with typical synaptonemal complexes. The significance of these complexes and of some other peculiar structures of germ cells, i.e., pore complexes and annuli within the nucleus, and annulate lamellae within the cytoplasm are discussed. The morphofunctional uniformity of some cytoplasmic structures (annulate lamellae, concentrically arranged ER, and yolk globules) in the oocyte as well as its nurse cells is also discussed.

Animals↗
PubMed1979

The abdominal muscle receptor organ in Astacus leptodactylus (Crustacea).

The structure of both the slow- and the fast-adapting abdominal muscle receptor organ of Astacus leptodactylus is described with particular reference to differences between the two systems. The receptors are composed of a thin muscle that extends from the front edge of one segment to the front edge of the following and a sensory cell connected with this muscle. In the zone where the sensory cells enter their respective muscle, muscle fibers are reduced (zone of relative muscle exclusion = ZRME) and partly replaced by connective tissue. The occurrence of dendritic processes of both the slow and the fast neurons is confined to this zone. The following differences between the two receptor types are established: (1) The fast receptor muscle reveals a smaller sarcomere length than the slow receptor muscle and a higher myosin/actin filament ratio. (2) Muscle fibers that pass the ZRME are always found at its periphery in the fast system, separated from dendritic processes by layers of connective tissue, while in the slow system muscle fibers frequently are intermingled with the sensory elements. (3) The ZRME of the slow receptor is 20-30% longer than that of the fast receptor. (4) The dendritic varicosities of the slow neuron, on an average, contain many more mitochondria than those of the fast neuron. (5) Dendritic processes (fine twigs as well as varicosities) are juxtaposed to the sarcolemma of the muscle fibers only in the slow system; in the fast system dendrites and muscle are spatially separated by connective tissue. It is assumed that these differences between the two receptor types are at least in part responsible for the different thresholds observed in physiological experiments.

Abdominal Muscles↗
PubMed1977

The diminution of Heterochromatic chromosomal segments in Cyclops (Crustacea, Copepoda).

The chromosomes of Cyclops divulsus, C. furcifer, and C. strenuus, like those of several other Copepods, undergo a striking diminution of chromatin early in embryogenesis. The process is restricted to the presumptive soma cells and occurs at the 5th cleavage in C. divulsus, at the 6th and 7th in C. furcifer, and at the 4th in C. strenus. The eliminated chromatin derives from the excision of heterochromatic chromosome segments (H-segments). Their chromosomal location is different in the three investigated species: Whereas in C. divulsus and C. furcifer the H-segments form large blocks-exclusively terminal in the former and terminal as well as kinetochoric in the latter-the germ line heterochromatin in C. strenuus is scattered all along the chromosomes. Extensive polymorphism exists with respect to the length of the terminal H-segments in C. furcifer, and with respect to the overall content of heterochromatin in the chromosomes of C. strenuus. In a local race of C. strenuus an extreme form of dimorphism has been found which is sex limited: females as a fule are heterozygous for an entire set of large (heterochromatin-rich), and a second set of small chromosomes in their germ line. Males are homozygous for the large set. In the first three cleavage divisions the H-polymorphism is solely expressed through differences of chromosome length. Following diminution the differences between homologous have disappeared. Feulgen cytophotometry demonstrates that in the three species the 1C DNA value for the germ line, as measured in sperm, is about twice that measured in somatic mitoses (germ line/soma C-values in picograms of DNA: C. strenuus 2.2/0.9, C. furcifer 2.9/1.44, C. divulsus 3.1/1.8). - The data imply that chromatin diminution is based on a mechanism which allows specific DNA segments, regardless of their location and size, to be cut out from the chromosomes without affecting the structural continuity of the remaining DNA. The mechanism may be analogous to that of prokaryotic DNA excision.

Animals↗