Elasmobranchii
Intercellular bridges between granulosa cells and the oocyte in the elasmobranch Raya asterias. (1/59)
In the present ultrastructural study intercellular bridges, connecting somatic granulosa cells to oocyte, have been detected for the first time and their modifications have been followed during Raja oogenesis. Intercellular bridges make their first appearance in small previtellogenic follicles as connecting devices between small cells and the oocyte. Later on, when the follicular epithelium becomes polymorphic and multilayered, for the presence of small, large, and pyriform-like cells, intercellular bridges link the oocyte and the different granulosa cells. Intercellular bridges contain ribosomes, whorl of membranes, mitochondria and vacuoles. Such cytoplasmic components are present also in the cell apex of large and pyriform-like cells thus suggesting, in agreement with other species (Motta et al. J. Exp. Zool., 1996;276:223-241) they may flow toward the oocyte. In this regard the presence of intercellular bridges during the oogenesis of cartilagineous fish may represent a crucial event of the active cooperation between granulosa cells and the oocyte. (+info)Retropositional parasitism of SINEs on LINEs: identification of SINEs and LINEs in elasmobranchs. (2/59)
Some previously unidentified short interspersed repetitive elements (SINEs) and long interspersed repetitive element (LINEs) were isolated from various higher elasmobranchs (sharks, skates, and rays) and characterized. These SINEs, members of the HE1 SINE family, were tRNA-derived and were widespread in higher elasmobranches. The 3'-tail region of this SINE family was strongly conserved among elasmobranchs. The LINEs, members of the HER1 LINE family, encoded an amino acid sequence similar to that encoded by the chicken CR1 LINE family, and they contained a strongly conserved 3'-tail region in the 3' untranslated region. This tail region of the HER1 LINE family was almost identical to that of the HE1 SINE family. Thus, the HE1 SINE family and the HER1 LINE family provide a clear example of a pair of SINEs and LINEs that share the same tail region. Conservation of the secondary structures of the tail regions, as well as of the nucleotide sequences, between the HE1 SINE family and HER1 LINE family during evolution suggests that SINEs utilize the enzymatic machinery for retroposition of LINEs through the recognition of higher-order structures of the conserved 3'-tail region. A discussion is presented of the parasitism of SINEs on LINEs during the evolution of these retroposons. (+info)The synaptic vesicle protein SV2 is complexed with an alpha5-containing laminin on the nerve terminal surface. (3/59)
Interactions between growing axons and synaptic basal lamina components direct the formation of neuromuscular junctions during nerve regeneration. Isoforms of laminin containing alpha5 or beta2 chains are potential basal lamina ligands for these interactions. The nerve terminal receptors are unknown. Here we show that SV2, a synaptic vesicle transmembrane proteoglycan, is complexed with a 900-kDa laminin on synaptosomes from the electric organ synapse that is similar to the neuromuscular junctions. Although two laminins are present on synaptosomes, only the 900-kDa laminin is associated with SV2. Other nerve terminal components are absent from this complex. The 900-kDa laminin contains an alpha5, a beta1, and a novel gamma chain. To test whether SV2 directly binds the 900-kDa laminin, we looked for interaction between purified SV2 and laminin-1, a laminin isoform with a similar structure. We find SV2 binds with high affinity to purified laminin-1. Our results suggest that a synaptic vesicle component may act as a laminin receptor on the presynaptic plasma membrane; they also suggest a mechanism for activity-dependent adhesion at the synapse. (+info)Low mass-specific brain Na+/K+-ATPase activity in elasmobranch compared to teleost fishes: implications for the large brain size of elasmobranchs. (4/59)
Elasmobranch fishes have long been noted for having unusually large brains for ectotherms, and therefore may be exceptions to the rule that vertebrates in general devote less than 8% of their resting metabolic rate to the central nervous system. The brain mass of sharks, skates and rays is often several times larger than that of teleost fishes of the same size. Still, the underlying reasons for this have remained unclear. Ion pumping by the Na+/K+-ATPase is the single most energy consuming process in the brain. In this study, Na+/K+-ATPase activity was measured in the brain of four species of elasmobranchs and 11 species of teleosts. While the average brain mass of the elasmobranchs examined was approximately three times that of the teleosts, the mean specific Na+/K+-ATPase activity was only about one-third of that of the teleosts. Thus, the total brain Na+/K+-ATPase activity was similar in elasmobranchs and teleosts. This suggests that the large brain size of elasmobranchs is at least partly related to a low mass-specific rate of brain energy use. (+info)The pit organs of elasmobranchs: a review. (5/59)
Elasmobranchs have hundreds of tiny sensory organs, called pit organs, scattered over the skin surface. The pit organs were noted in many early studies of the lateral line, but their exact nature has long remained a mystery. Although pit organs were known to be innervated by the lateral line nerves, and light micrographs suggested that they were free neuromasts, speculation that they may be external taste buds or chemoreceptors has persisted until recently. Electron micrographs have now revealed that the pit organs are indeed free neuromasts. Their functional and behavioural role(s), however, are yet to be investigated. (+info)Detection and processing of electromagnetic and near-field acoustic signals in elasmobranch fishes. (6/59)
The acoustic near field of quietly moving underwater objects and the bio-electric field of aquatic animals exhibit great similarity, as both are predominantly governed by Laplace's equation. The acoustic and electrical sensory modalities thus may, in directing fishes to their prey, employ analogous processing algorithms, suggesting a common evolutionary design, founded on the salient physical features shared by the respective stimulus fields. Sharks and rays are capable of orientating to the earth's magnetic field and, hence, have a magnetic sense. The electromagnetic theory of orientation offers strong arguments for the animals using the electric fields induced by ocean currents and by their own motions in the earth's magnetic field. In the animal's frame of reference, in which the sense organs are at rest, the classical concept of motional electricity must be interpreted in relativistic terms. In the ampullae of Lorenzini, weak electric fields cause the ciliated apical receptor-cell membranes to produce graded, negative receptor currents opposite in direction to the fields applied. The observed currents form part of a positive-feedback mechanism, supporting the generation of receptor potentials much larger than the input signal. Acting across the basal cell membranes, the receptor potentials control the process of synaptic transmission. (+info)Contractile properties of the elasmobranch rectal gland. (7/59)
The importance of the rectal gland in elasmobranch osmoregulation is well established. The rate of secretion by the gland is under the control of a variety of secretagogues and inhibitors. Early morphological work suggested that a band of smooth muscle cells surrounds the periphery of the shark rectal gland between the secretory tubules and the connective tissue capsule. To confirm the presence of the muscle ring, we examined histological sections from two species of shark, Squalus acanthias and Carcharodon carcharius, and from the stingray Dasyatis sabina and stained sections from S. acanthias with the actin-specific ligand phalloidin. In all three species, a distinct band of what appeared to be smooth muscle cells was evident, and the putative muscle ring in S. acanthias stained specifically with phalloidin. Moreover, isolated rings of rectal gland tissue from S. acanthias constricted when acetylcholine or endothelin was applied and responded to nitric oxide with an initial dilation, followed by a more substantial constriction. Subsequent addition of porcine C-type natriuretic peptide dilated the rings, but two prostanoids (carbaprostacyclin and prostaglandin E(1)) did not change ring tension significantly. The rings did not respond to the endothelin-B-specific agonist sarafotoxoin S6c, suggesting that the response to endothelin was mediated via endothelin-A-type receptors. Our data confirm the presence of a smooth muscle ring in the periphery of the elasmobranch rectal gland and demonstrate that the gland responds to a suite of smooth muscle agonists, suggesting that changes in the dimensions of the whole rectal gland may play a role in its secretory function. (+info)Digenea and acanthocephala of elasmobranch fishes from the southern coast of Brazil. (8/59)
New records for helminth species recovered from elasmobranch fishes in Brazil are established. Digenean and acanthocephalan parasites of elasmobranch fishes are reported from the southern coast of Brazil: Otodistomum veliporum (Creplin, 1837) Stafford, 1904 (Digenea: Azygiidae) in the stomach and spiral valve of Dipturus trachydermus and in the spiral valve of Squatina sp. Cystacanths and juveniles of the acanthocephalans Corynosoma australe Johnston, 1937 and Corynosoma sp., in the spiral valve of Squatina sp., Galeorhinus galeus and Hexanchus griseus and in the stomach of Squalus megalops; a juvenile of Gorgorhynchus sp., in the spiral valve of Sphyrna zygaena. Dipturus trachydermus and Squatina sp. are new host records for O. veliporum. Digeneans and acanthocephalans are reported for the first time parasitizing elasmobranch fishes in Brazil. (+info)'Elasmobranchii' is a superorder in the class Chondrichthyes, which includes all sharks, skates, rays, and sawfishes. This group is characterized by several distinct features, including:
1. Cartilaginous skeletons: Unlike bony fishes, elasmobranchs have skeletons made of cartilage rather than bone.
2. Five to seven gill slits: Most elasmobranchs have five pairs of gill slits on each side of their body, although some species may have six or seven pairs. These gill slits are open to the outside environment and lack protective covers found in bony fishes.
3. Heterocercal tail: Elasmobranchs possess a unique tail structure called a heterocercal tail, where the upper lobe is longer than the lower lobe. This tail design provides powerful propulsion and maneuverability in the water.
4. Dermal denticles: The skin of elasmobranchs is covered with small, tooth-like structures called dermal denticles, which provide a protective covering and reduce friction while swimming.
5. No swim bladders: Unlike bony fishes, elasmobranchs do not have a gas-filled swim bladder to help maintain buoyancy. Instead, they rely on their large liver, which contains low-density oil, to provide some degree of buoyancy.
6. Electrosensory organs: Many elasmobranchs possess specialized sensory organs called the ampullae of Lorenzini, which allow them to detect electric fields generated by living organisms and other environmental sources. This ability aids in hunting, navigation, and communication.
7. Carnivorous diet: Elasmobranchs are primarily carnivorous, feeding on various marine animals such as fish, squid, and crustaceans. Some species may also consume smaller elasmobranchs.
8. Live birth or egg laying: Most elasmobranchs reproduce by giving live birth (viviparity), where the embryos develop inside the mother's body and receive nourishment through a placenta-like structure. However, some species lay eggs (oviparity) in protective cases called mermaid's purses.
9. Slow growth and late maturity: Elasmobranchs generally grow slowly and reach sexual maturity at a relatively advanced age compared to many bony fishes. This slow life history makes them particularly vulnerable to overfishing and other human-induced threats.
Elasmobranchii
Lebachacanthus
Brygmophyseter
Rybushka Formation
Sclerorhynchus
Taxonomy of the vertebrates (Young, 1962)
Fadenia
Lestrodus
Stethacanthidae
Campodus
Symmoriiformes
Helicoprion
Ganges shark
Squatinactis
Cladoselache
Ornithocheiridae
Smalltooth sand tiger
Edestus
Caseodus
Barbclabornia
Agassizodus
Toxoprion
Megalodon
2012 in fish paleontology
Pseudocoracidae
Myledaphus
Paraisurus
Nanocorax
Pseudoscapanorhynchus
Doliobatis
Elasmobranchii - Wikipedia
Another word for ELASMOBRANCHII > Synonyms &...
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elasmobranchii - Nix Illustration
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Chondrichthyes2
- Elasmobranchii (/ɪˌlæzməˈbræŋkiaɪ/) is a subclass of Chondrichthyes or cartilaginous fish, including sharks (superorder Selachii), rays, skates, and sawfish (superorder Batoidea). (wikipedia.org)
- Elasmobranchii is one of the two subclasses of cartilaginous fish in the class Chondrichthyes, the other being Holocephali (chimaeras). (wikipedia.org)
Sharks1
- Mineral homeostasis and regulation of mineralization processes in the skeletons of sharks, rays and relatives (Elasmobranchii). (mpg.de)
Fishes1
- The name Elasmobranchii comes from the Ancient Greek words elasmo- ("plate") and bránchia ("gill"), referring to the broad, flattened gills which are characteristic of these fishes. (wikipedia.org)
Squatinidae1
- Shifting baselines for common angelshark, Squatina squatina (Elasmobranchii: Squatinidae), in the Northern Adriatic Sea (Mediterranean Sea). (ogs.it)
Subclass4
- Elasmobranchii (/ɪˌlæzməˈbræŋkiaɪ/) is a subclass of Chondrichthyes or cartilaginous fish, including sharks (superorder Selachii), rays, skates, and sawfish (superorder Batoidea). (wikipedia.org)
- Members of the elasmobranchii subclass have no swim bladders, five to seven pairs of gill clefts opening individually to the exterior, rigid dorsal fins, and small placoid scales. (wikipedia.org)
- Sharks, together with rays and skates , make up the subclass Elasmobranchii of the Chondrichthyes. (britannica.com)
- Elasmobranch (subclass Elasmobranchii) is a group of cartilaginous fishes that include sharks (superorder Selachii) and rays (superorder Batoidea). (frontiersin.org)
Holocephali2
- Elasmobranchii is one of the two subclasses of cartilaginous fish in the class Chondrichthyes, the other being Holocephali (chimaeras). (wikipedia.org)
- They are divided into two subclasses: Elasmobranchii (sharks, rays, and skates) and Holocephali (chimaera, sometimes called ghost sharks). (newworldencyclopedia.org)
Neoselachii1
- Nouvelles faunes de Sélaciens (Elasmobranchii, Neoselachii) de l'Éocène moyen des Landes (Sud−Ouest, France). (palass.org)
Mesozoic and Cenozoic Elasmobranchii1
- Mesozoic and Cenozoic Elasmobranchii, Chondrichthyes II. (palass.org)
Rays1
- The Elasmobranchii are sometimes divided into two superorders, Selachimorpha (sharks) and Batoidea (rays, skates, sawfish). (newworldencyclopedia.org)
Vertebrata1
- Subfilos Cephalochordata (Acrania y Vertebrata (Acrania) - Lista de especies registradas en Cuba (octubre de 2006). (si.edu)
Potamotrygonidae1
- Apicomplexa: Haemogregarinidae) from a freshwater Cururu Stingray Potamotrygon cf. histrix (Elasmobranchii: Potamotrygonidae), from the Amazon Region, Brazil. (nih.gov)
Species1
- Computer Generated Species Richness Map for Elasmobranchii. (aquamaps.org)