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At least 37 records · Page 2Linked to original sources
PubMed2003

Shallow-water Campanulariidae (Hydrozoa, Leptothecatae) from northern Bahía, Brazil.

This study provides the first semi-quantititative account of the benthic campanulariid hydroids from Northern Bahia (Brazil), down to a depth of 60 m, based largely on collections obtained since 1992. Colonies were collected from six habitats along the coast of Salvador City, Todos os Santos Bay, Itaparica Island and at the northernmost part of the coast of the State of Bahia. From the 982 colonies examined, nine species were recorded: Campanularia hincksii, Clytia gracilis, C. hemisphaerica, C. hummelincki, C. linearis, C. macrotheca, C. noliformis, Obelia bidentata and O. dichotoma. Following a defined abundance scale, Clytia gracilis and C. noliformis were the most abundant species, whereas Campanularia hincksii and Clytia hummelincki were rare. Cluster analysis of relative abundance data revealed sandy shores had a markedly different hydroid community from other habitats. A simplified identification key, redescriptions, illustrations and data on nematocyst compliment are provided for each species. Campanularia hincksii, Clytia macrotheca and C. noliformis are reported from Brazil for the first time.

Animals↗
PubMed2000

Origin of germ cells, sex determination, and sex inversion in medusae of the genus Clytia (Hydrozoa, leptomedusae): the influence of temperature.

In Cnidaria, a separation between soma and germline remains unclear. In this work, we studied the origin of germinal cells and determination of the sexual phenotype in Clytia hemisphaerica and Clytia sp. Colonies of C. Hemisphaerica were cultivated and the medusae liberated by each colony raised until maturity. Two hermaphrodite colonies were obtained, liberating male and female medusae. These two colonies and their medusae were raised at 15 degrees C, 21 degrees C, or 24 degrees C. The medusae budded and cultured at 24 degrees C were mainly female (80%). In contrast, if the medusae were released at 15 degrees C, at whatever temperature they were raised later, they were mainly male (85%). The same occurred if, after release at 24 degrees C but before the formation of the gametes, they were kept at 15 degrees C for at least 24 hr. We suggest that there are two subpopulations of germ cells. The female line will be dominant at 24 degrees C but temperature sensitive, with inhibition of this line by a temperature drop to 15 degrees C, this inverting the population sex-ratio. The irreversible action of a temperature drop to 15 degrees C supports the view that the germ cells are isolated very early. In C. hemisphaerica, hermaphrodite medusae were never observed. On the contrary, in Clytia sp., probably a new species, we have found male, female, but also hermaphrodite specimens. This is the second definite example of hermaphroditism described in any hydromedusan. The transformation of female into hermaphrodite then into male specimens occurs at 13 degrees C. These results demonstrate the unstable character of genetic sex determination in cnidarians, at least in certain species.

Animals↗
PubMed1994

Possible involvement of arachidonic acid and eicosanoids in metamorphic events in Hydractinia echinata (Coelenterata; Hydrozoa).

Upon induction of metamorphosis, larvae of the marine hydroid Hydractinia echinata release [14C]-arachidonic acid from previously labeled endogenous sources. The lipoxygenase inhibitors nordihydroguaiaretic acid and 5,8,11,14-eicosatetraynoic acid inhibited metamorphosis induced by Cs+ and 1,2-sn-dioctanoylglycerol, whereas the inhibitors of cyclooxygenase, indomethacin, and acetylsalicylic acid were ineffective, suggesting a role for lipoxygenase metabolites of arachidonic acid in induction of metamorphosis. Lipoxygenase products in Hydractinia echinata were isolated and identified by gas chromatography/mass spectrometry. 8- and 12-HETE were the most abundant metabolites. In cytosolic fractions from larvae activity of an arachidonic acid metabolizing enzyme, presumably a lipoxygenase, was found. The metabolic product was identified by 1H-NMR and chiral phase HPLC as 8(R)-HETE. Its production was strongly inhibited by NDGA, but not by indomethacin.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1994

Metamorphosin A: a novel peptide controlling development of the lower metazoan Hydractinia echinata (Coelenterata, Hydrozoa).

Animal development depends on cell communication by signals. We have investigated the role of signals and of signal transduction in the development of the marine hydroid Hydractinia echinata. The larvae undergo metamorphosis in response to a chemical signal provided by environmental bacteria. Metamorphosis can be induced by a variety of different compounds interfering with biochemical signal transduction pathways. Sectioned posterior parts cannot be induced by most compounds known to induce whole larvae to metamorphose. We identified a novel peptide, pGlu-Gln-Pro-Gly-Leu-TrpNH2 ("metamorphosin A"), which induces isolated posterior parts to undergo metamorphosis and hence reactivates pattern formation, cell proliferation, cell differentiation, and morphogenesis. We suggest this peptide to be part of an internal signaling system involved in control of metamorphosis.

Amino Acid Sequence↗
PubMed2001

First identification and localization of a visual pigment in Hydra (Cnidaria, Hydrozoa).

The cnidarian Hydra does not possess identified photoreceptive structures or specialized cells for light detection; nevertheless, it shows a marked photosensitivity. So far no evidence has been previously reported about the localization of the proteins involved in the photoresponse. We used polyclonal antibodies and immunofluorescence microscopy on whole-mount Hydra to identify a putative rhodopsin-like protein. Our results show an immunoreactivity in the ectodermal layer of Hydra, which corresponds in position to the nervous epidermal sensory cells. These data provide the first identification of a rhodopsin-like protein in a phylogenetically old invertebrate and give a new insight into the Hydra photoreceptive response.

Animals↗
PubMed1984

Migration of I-cells from ectoderm to endoderm in Hydra attenuata Pall (Cnidaria, Hydrozoa) and their subsequent differentiation.

The cellular composition of isolated ecto- and endoderm of the gastric column of Hydra attenuata Pall were recorded qualitatively and quantitatively. The endoderm contains a small population of I-cells ("basal cells") which give rise to the endodermal neurons. The recombination of live ecto- and endoderm, one of which had previously been [3H]thymidine labeled, revealed that the endodermal I-cells and their neural derivatives originate from ectodermal I-cells which migrate across the mesoglea. No other cell types were found to pass from one cell layer to the other. The experiments support the idea that the endodermal gland cells constitute an autoreproductive cell line independent of the pluripotent I-cells.

Animals↗
PubMed1986

Cholinergic mechanism in Liriope tetraphylla (Cnidaria, Hydrozoa).

Crude whole body homogenates of Liriope tetraphylla exhibit a cholinesterase particularly active on acetylthiocholine but not on butyrylthiocholine. The acetylthiocholine hydrolysis is completely blocked by neostigmine. The Michaelis-Menten constant for acetylthiocholine is 0.14 mM. The pharmacological analysis of the responses to the choline esters nicotine and atropine suggests the involvement in Liriope tetraphylla of a cholinergic mechanism in the pointing reflex. Butyrylcholine, nicotine and atropine (but not muscarinic agonists) caused the contraction of the subumbrellar radial muscles. The effects of atropine were dose-dependent and were depressed in competition with muscarinic agonists. MgCl2 interfered with the action of atropine. The results were explained by suggesting the existence, at least at the neuromuscular junction, of excitatory (nicotinic) and inhibitory (muscarinic) pre-synaptic receptors modulating the release of the (unknown) transmitter acting post-synaptically.

Animals↗
PubMed1989

Inotropic response elicited by nematocyst contents of Hydra oligactis (Coelenterata: Hydrozoa).

1. Intact, isolated nematocysts from the non-toxic, freshwater coelenterate Hydra oligactis contain soluble material(s) capable of producing a sustained increase in the rate of developed force in the vertebrate myocardium. 2. The positive inotropic effects of this material(s) appear grossly comparable to those described for Anthopleurin-A (AP-A) and Toxin II (ATX-II) from sea anemones. 3. The effects of the nematocyst material are distinct from those of known vasoactive peptides reported to occur in Hydra.

Animals↗
PubMed2002

Envenomation by a benthic Hydrozoa (Cnidaria): the case of Nemalecium lighti (Haleciidae).

A case of envenomation caused by the Nemalecium lighti is described. The hydrozoan species lives in many kinds of substrates, being quite common in tropical shallow water. The patient, a marine biologist, had contact with the animal in two different opportunities while snorkeling. Both contacts produced erythematous and highly pruriginous papules in exposed areas of the body. The signs and symptoms persisted for a week and healed without sequellae.

Animals↗
PubMed2002

The toxicity of copper, cadmium and zinc to four different Hydra (Cnidaria: Hydrozoa).

An acute toxicity study of three metals to Hydra species carried out using two different assessment methods, (i) determination of the LC50 and (ii) measurement of progressive morphological changes, demonstrated that relative toxicity decreased from copper to cadmium with zinc the least toxic for all species. The latter method revealed more details of the effect on Hydra in terms of physical damage to the polyp but both methods indicated that H. viridissima was more sensitive to copper and cadmium than H. vulgaris1 (Zurich strain, male clone), H. vulgaris2 (a dioecious strain reproducing sexually and asexually) and H. oligactis (dioecious, reproducing sexually and asexually). The responses to zinc were similar for all Hydra. The possible role of metabolic interactions between H. viridissima and its symbiotic green algae in contributing to the greater sensitivity of this polyp is discussed.

Animals↗
PubMedDate not supplied

Photobehaviour of Hydra (Cnidaria, Hydrozoa) and correlated mechanisms: a case of extraocular photosensitivity.

The morpho-functional organization correlated to photosensitivity in Cnidaria is that of ocelli and extraocular photoreception. Several examples of the second type of organization are reported. The photosensitivity of the cnidarian Hydra is of the extraocular (neural or dermal) type. The effects of photic stimulation (applied according to various experimental protocols: steady condition; step stimulus; single, twin, or repetitive pulses; different polarities and chromaticities of steady, step and pulse stimulation and different phases of pulse application) on the modulation of various bioelectric events linked to the periodic behaviour of the animal are reviewed. The mechanisms correlated with the photobehaviour of Hydra, as well as the problems still open on the molecular mechanisms of phototransduction, are discussed.

Animals↗
PubMed1998

Over one-half billion years of head conservation? Expression of an ems class gene in Hydractinia symbiolongicarpus (Cnidaria: Hydrozoa).

We report the isolation of an empty spiracles class homeodomain-containing gene, Cn-ems, from the hydrozoan Hydractinia symbiolongicarpus, the first gene of this class characterized in a lower metazoan. Cn-ems was found to be expressed in the head of gastrozooids, specifically in endodermal epithelial cells of the taeniolae of the hypostome. Cn-ems is not expressed in gonozooids, which lack taeniolae. Experimental conversion of the posterior region of the planula larva into head structures up-regulates expression of the gene. These findings establish that the association of ems-class genes with head structures preceded the evolution of bilateral symmetry.

Amino Acid Sequence↗
PubMed1996

Transmission genetics of allorecognition in Hydractinia symbiolongicarpus (Cnidaria:Hydrozoa).

Allorecognition is ubiquitous, or nearly so, amongst colonial invertebrates. Despite the prominent role that such phenomena have played both in evolutionary theory and in on the origin of the vertebrate immune system, unambiguous data on the transmission genetics of fusibility (i.e., the ability of two individuals to fuse upon tissue contact) is lacking for any metazoan outside of the phylum Chordata. We have developed lines of the hydroid Hydractinia symbiolongicarpus (Phylum Cnidaria) inbred for fusibility and here report results of breeding experiments establishing that fusibility segregates as expected for a single locus with codominantly expressed alleles, with one shared allele producing a fusible phenotype. Surveys of fusibility in field populations and additional breeding experiments indicate the presence of an extensive allele series.

Alleles↗