Search

A stable phylogenetic hypothesis for families within jellyfish class Scyphozoa has been elusive. Reasons for the lack of resolution of scyphozoan familial relationships include a dearth of morphological characters that reliably distinguish taxa and incomplete taxonomic sampling in molecular studies. Here, we address the latter issue by using maximum likelihood and Bayesian methods to reconstruct the phylogenetic relationships among all 19 currently valid scyphozoan families, using sequence data from two nuclear genes: 18S and 28S rDNA. Consistent with prior morphological hypotheses, we find strong evidence for monophyly of subclass Discomedusae, order Coronatae, rhizostome suborder Kolpophorae and superfamilies Actinomyariae, Kampylomyariae, Krikomyariae, and Scapulatae. Eleven of the 19 currently recognized scyphozoan families are robustly monophyletic, and we suggest recognition of two new families pending further analyses. In contrast to long-standing morphological hypotheses, the phylogeny shows coronate family Nausithoidae, semaeostome family Cyaneidae, and rhizostome suborder Daktyliophorae to be nonmonophyletic. Our analyses neither strongly support nor strongly refute monophyly of order Rhizostomeae, superfamily Inscapulatae, and families Ulmaridae, Catostylidae, Lychnorhizidae, and Rhizostomatidae. These taxa, as well as familial relationships within Coronatae and within rhizostome superfamily Inscapulatae, remain unclear and may be resolved by additional genomic and taxonomic sampling. In addition to clarifying some historically difficult taxonomic questions and highlighting nodes in particular need of further attention, the molecular phylogeny presented here will facilitate more robust study of phenotypic evolution in the Scyphozoa, including the evolution characters associated with mass occurrences of jellyfish. doi: 10.1093/icb/icq074

Mycoplasma mobile, a parasitic bacterium lacking a peptidoglycan layer, glides on solid surfaces in the direction of a membrane protrusion at a cell pole by a unique mechanism. Recently, we proposed a working model in which cells are propelled by leg proteins clustering at the protrusion's base. The legs repeatedly catch and release sialic acids on the solid surface, a motion that is driven by the force generated by ATP hydrolysis. Here, to clarify the subcellular structure supporting the gliding force and the cell shape, we stripped the membrane by Triton X-100 and identified a unique structure, designated the 'jellyfish' structure. In this structure, an oval solid 'bell' [approximately equal to] 235 wide and 155 nm long is filled with a 12-nm hexagonal lattice and connected to this structure are dozens of flexible 'tentacles' that are covered with particles of 20-nm diameter at intervals of [approximately equal to] 30 nm. The particles appear to have 180[degrees] rotational symmetry and a dimple at the center. The relation of this structure to the gliding mechanism was suggested by its cellular localization and by analyses of mutants lacking proteins essential for gliding. We identified 10 proteins as the components by mass spectrometry and found that these do not show sequence similarities with other proteins of bacterial cytoskeletons or the gliding proteins previously identified. Immunofluorescence and immunoelectron microscopy revealed that two components are localized at the bell and another that has the structure similar to the [F.sub.1]-ATPase [beta] subunit is localized at the tentacles. bacteria | electron microscopy | gliding motility | immunofluorescence | protein identification

Two types of metamorphosis occur in the life cycle of Carybdea marsupialis Linnaeus 1758 (Cubozoa, Carybdeidae). In addition to the metamorphosis described several times over, during which the entire polyp transforms into one medusa, we investigated a second type of metamorphosis which leaves a regenerative remnant. This mode of medusa formation seems to be derived from the strobilation known from Scyphozoa. Both types are described and the implications these results have on the idea about the origin of the class Cubozoa, are discussed., Introduction Although cubomedusae are well known from the literature due to their potential to cause life threatening envenomations in humans (for review see Burnett 1996), little is known about their [...]

The annual cycle of abundance and distribution of the scyphozoan medusae Aurelia aurita and Cyanea capillata was studied in the Bornholm Basin (central Baltic Sea) in 2002. Seasonal changes in prey composition and predatory impact were investigated by analyzing stomach contents. A. aurita occurred from July to November, with a maximum mean abundance of 2.3 ind. per 100 [m.sup.3] in August, whereas C. capillata was caught in much smaller numbers from July to September. No ephyrae of either species were found; therefore, advection of medusae from the western Baltic Sea is assumed. From July to October, ~80% of A. aurita medusae was distributed in the upper 20 m above the thermocline, whereas C. capillata occurred only in the halocline below 45 m. A. aurita did not migrate vertically and fed mainly on the most abundant cladoceran species Bosmina coregoni maritima. Further prey organisms were the cladocerans Evadne nordmanni and Podon spp., mollusk larvae and copepods. Copepod nauplii and copepodite stages I-III were not eaten by the medusae, neither were fish eggs and larvae used as prey. Based on mean medusa and zooplankton abundance from the upper 20 m, the predatory impact was very low. In August, when mean abundance of A. aurita was highest, only 0.1% of the copepod and 0.5% of the cladoceran standing stock were eaten per day. However, in regions with higher medusa or lower zooplankton abundance, up to 7.9% of the cladoceran standing stock was consumed per day. Hence, A. aurita did not regulate the zooplankton community in the Bornholm Basin, and fish larvae did not suffer from competition with and predation by the medusae.

We have clarified, for the first time, the spatiotemporal patterns of intracellular [Ca.sup.2+] increases at fertilization and the [Ca.sup.2+]-mobilizing mechanisms in eggs of hydrozoan jellyfish, which belong to the evolutionarily old diploblastic phylum, Cnidaria. An initial [Ca.sup.2+] increase just after fertilization took the form of a [Ca.sup.2+] wave starting from one cortical region of the egg and propagating to its antipode in all of four hydrozoan species tested: Cytaeis uchidae, Cladonema pacificum, Clytia sp., and Gonionema vertens. The initiation site of the [Ca.sup.2+] wave was restricted to the animal pole, which is known to be the only area of sperm-egg fusion in hydrozoan eggs, and the wave propagating velocity was estimated to be 4.2-5.9 [micro]m/s. After a [Ca.sup.2+] peak had been attained by the initial [Ca.sup.2+] wave, the elevated [Ca.sup.2+] gradually declined and returned nearly to the resting value at 7-10 min following fertilization. Injection of inositol 1,4,5-trisphosphate (I[P.sub.3]), an agonist of I[P.sub.3] receptors (I[P.sub.3]R), was highly effective in inducing a [Ca.sup.2+] increase in unfertilized eggs; I[P.sub.3] at a final intracellular concentration of 12-60 nM produced a fully propagating [Ca.sup.2+] wave equivalent to that observed at fertilization. In contrast, a higher concentration of cyclic ADP-ribose (cADPR), an agonist of ryanodine receptors (RyR), only generated a localized [Ca.sup.2+] increase that did not propagate in the egg. In addition, caffeine, another stimulator of RyR, was completely without effect. Sperm-induced [Ca.sup.2+] increases in Gonionema eggs were severely affected by preinjection of heparin, an inhibitor of [Ca.sup.2+] release from I[P.sub.3]R. These results strongly suggest that there is a well-developed I[P.sub.3]R-, but not RyR-mediated [Ca.sup.2+] release mechanism in hydrozoan eggs and that the former system primarily functions at fertilization. Our present data also demonstrate that the spatial characteristics and mechanisms of [Ca.sup.2+] increases at fertilization in hydrozoan eggs resemble those reported in higher triploblastic animals. Keywords: Fertilization; Hydrozoan egg; Calcium; I[P.sub.3]; cADPR; Caffeine; Cytaeis; Cladonema; Clytia; Gonionema

The work of some researchers into the box jellyfish, the sting of which is capable of killing a human within minutes, is examined. Heather Walling, a research officer at the Cooperative Research Centre's Reef Research Centre at James Cook University in north Queensland, Australia, and Lisa-ann Gershwin, a doctoral student at the Australian Institute of Marine Science, are both doing research into the box jellyfish in order to find an antidote for its sting.

Crystallins, the major water-soluble proteins of the lens, are well conserved but unexpectedly diverse and often differ among species. In many cases, crystallins have been recruited for their specialized role in the lens from stress proteins (especially small heat shock proteins) and ubiquitously expressed enzymes in a process we call `gene sharing'. Gene sharing means that a gene encodes a protein that is used for at least two entirely different tasks. Taxon-specific accumulation of ubiquitously expressed proteins suggesting gene sharing also occurs in the cornea. 'Borrowing' of diverse proteins to be used as lens crystallins occurs in jellyfish (which have astonishingly complex eyes) and molluscs (cephalopods and scallops) as well as vertebrates. For example, glutathione S-transferase and aldehyde dehydrogenase have been recruited as lens crystallins in mollusks. The cnidarian cubomedusan jellyfish, Tripedalia cystophora, has three lens crystallins. One, J3, is homolgous to vertebrate saposins, which are multifunctional proteins that bridge lysosomal hydrolases to membrane lipids aiding metabolic turnover. The characteristic saposin motif is also found in enzymes and may regulate their activity. J3-crystallin is expressed in the lens, statocyst and tentacle of the jellyfish, suggesting that it is multifunctional. Thus, the jellyfish J3-crystallin reflects both the chaperone and enzyme connections of the vertebrate crystallins. This principle of performing a specialized task (transparency and refraction) with ubiquitous proteins differs from divergent evolution. The similarity in the structure and function of cis-regulatory elements of vertebrate and invertebrate crystallin genes supports the idea that lens-preferred gene expression is a major determinant of crystallin evolution.

Many aquatic animals change their body shape as they grow larger and it is unclear how such change influences swimming performance. The scyphozoan jellyfish Aurelia aurita increases its mass by as much as three orders of magnitude in a lifetime and their bodies change from being prolate (more tall than wide) as juveniles to being oblate (more wide than tall) as adults. Does this change in body shape facilitate higher swimming performance than if these jellyfish maintained the same shape over their ontogeny? We addressed this question by measuring the body shape and swimming kinematics of jellyfish spanning nearly three orders of magnitude in body size and by mathematically modeling the hydrodynamics of their swimming. We found that larger jellyfish swam with a lower pulse frequency, a disproportionately slower speed and lower propulsive efficiency. Mathematical simulations of swimming suggest that having an oblate body shape throughout ontogeny would result in lower swimming speed and propulsive efficiency over a lifetime. However, our simulations also suggest that speed and efficiency would be greater if jellyfish maintained a prolate body shape throughout ontogeny.