كسيوبيا

Sachs and Wilcox (2006) studied the impact of Symbiodinium microadriaticum, a dinoflagellate algal symbiont of the upside-down jellyfish "Cassiopea xamachana", on its host. Cassiopea are born symbiont-free, disperse from their mother as planula larvae, and acquire algae infectiously (from the environment) once they have reached the sessile polyp stage. The asexual polyps can reproduce via clonal budding and infected polyps transmit algae to nascent offspring via vertical transmission (i.e., parent to offspring bud). Once infected, polyps undergo metamorphosis to the adult medusa stage. Both polyps and medusae expel a proportion of their algal symbionts back into the environment. Sachs and Wilcox carried out experiments to investigate the conditions under which the Cassiopea-dinoflagellate mutualism might evolve away from a mutually beneficial relationship in the direction of parasitism (i.e., where costs to the host outweigh any benefits to the host). Their results provide interesting insight into factors that may prevent this dinoflagellate symbiont from evolving increased virulence and becoming a parasite of Cassiopea (Sachs and Wilcox 2006).

The species traditionally known as C. xamachana (see taxonomy section), and to a lesser extent Cassiopea frondosa, is attacked by the predatory Jellyfish-eating Nudibranch Dondice parguerensis, which may be found lurking among Cassiopea's lappets (Brandon and Cutress 1985). This small nudibranch (sea slug), which is less than 5 cm long, can be found year round on the underside of Cassiopea, but Brandon and Cutress found it to be most abundant from September to February, with the highest proportion of juveniles found from November to March. It is essentially a parasite, living, feeding, and breeding on the oral arms of these jellyfish. Brandon and Cutress found between 27 and 80% of the Cassiopea at a site harboring Dondice parguerensis, not uncommonly with as many as four nudibranchs on a single jellyfish (mean 2.3, maximum 11). Grazed body parts are normally regenerated by the medusa at about the same rate at which they are consumed, athough sometimes significant damage is apparent (Brandon and Cutress 1985). The medusa's stinging nematocysts are apparently stored by Dondice parguerensis and used for defense by the nudibranch, which discharges them in response to rough handling (Brandon and Cutress 1985).

The upside-down (or mangrove) jellyfish, Cassiopea, is a large jellyfish (up to about 30 cm in diameter) that is brown or olive and creamy white in color. Its underside is covered with extensions (oral arms) that branch into thousands of lacy extensions (lappets). These lappets contain thousands of photosynthetic yellow-brown zooxanthellae (mutualistic photosynthetic dinoflagellate algae). The lower margin of the bell is surrounded by multibranched tentacles. Cassiopea swims in the typical jellyfish orientation, with its mouth facing downward. However, unlike most jellyfish, Cassiopea is seldom seen swimming, instead spending much of its time flipped upside down, pulsating, on sandy or muddy substrates in mangrove or soft bottom bay habitats. This orientation provides its photosynthetic zooxanthellae with critical access to light (Kaplan 1988; Fitt and Costley 1998).

In Cassiopea, as in many jellyfish, the scyphistoma (polyp stage) forms asexually produced vegetative buds, which detach from the polyp and metamorphose into new scyphistomae. Once polyps are infected with zooxanthellae, they form medusae (the life stage most people think of as a "jellyfish") asexually by a process known as strobilation, which involves repeated transverse fission of the scyphistoma (Ojimi et al. 2009).

Cassiopea is not a strong natural disperser, and its global distribution may therefore be the result of sweepstakes dispersal in which long-distance gene flow is extremely rare (Holland et al. 2004).

Cassiopea is widely distributed in the tropical Pacific and western Atlantic (see discussion in Systematics and Taxonomy section). Although Cassiopea occurs in Bermuda, south Florida marks the northern limit of the main range of the Caribbean Cassiopea species. These jellyfish inhabit shallow, soft bottomed mangrove lagoons of Florida Bay (Fleck and Fitt 1999).

Cassiopea is a bottom-dweller, living in areas with relatively clear, shallow water (necessary to allow photosynthesizing symbionts in the oral surface to receive sufficient light during the day). It occurs in shallow, tropical lagoons, mangrove swamps, and sandy mudflats. Mangrove sheltered habitat is favorable for Cassiopea reproduction as degrading mangrove leaves provide primary settlement sites and possibly metamorphic cues for sexual and asexual propagules (Fleck and Fitt 1999; Hofmann and Hadfield 2002; Muller and Leitz 2002). In some muddy areas, dozens of Cassiopea medusae may cover the bottom (Kaplan 1988).

The genus Cassiopea is distinctive, but at this point taxonomy within the genus is not yet well enough resolved to recognize species morphologically, with the apparent exception of C. frondosa (Holland et al. 2004). The underside of C. frondosa is so frilly that oral arms are not visible. Oral arms are as long as the disk is wide, so lappets extending from the arms are not visible from above. In its range in the Caribbean, Florida, and Bermuda, C. frondosa is more common in turtle grass beds, while other Cassiopea are more often found in channels in mangrove swamps (Kaplan 1988).

Adult female Cassiopea incorporate sperm released into the surrounding water by males. They envelop the internally fertilized eggs in mucus and wrap this mass around the base of sex-specific vesicles, thus protecting the embryos until the ciliated planula larvae hatch from the egg envelopes. In addition to sexually generated planulae, Cassiopea also produces planula-like swimming bodies by asexual budding. Both types of larvae, whether produced sexually or asexually, have to find a hard substrate on which to settle and transform into a polyp (scyphistoma) (Muller and Leitz 2002).

Bigelow (1900, cited in Ojimi et al. 2009) reported that the smallest specimen of "Cassiopea xamachana" found to contain eggs measured 6.5 cm in diameter.

Like some other introduced scyphozoans, Cassiopea are capable of colonizing large nearshore areas and producing problematic blooms (Mills 2001, cited in Holland et al. 2004). Coastal eutrophication, habitat disturbance, and mangrove filling have been identified as important factors driving large-scale increases of "C. xamachana" in the Bojorquez Lagoon, Mexico (Arai 2001, cited in Holland et al. 2004).

The taxonomy of Cassiopea is currently unsettled. Historically, six Cassiopea species were described from the Pacific. However, for most of the past several decades these multiple names have all been treated as representing just a single valid Pacific species, Cassiopea andromeda. In addition to this single Pacific species, two other species, C. frondosa, and C. xamachana, have long been recognized from the region encompassing the Caribbean, Florida, and Bermuda (Holland et al. 2004). Furthermore, Cassiopea were apparently accidentally introduced at least once to the Hawaiian Islands early in the 20th century. As a consequence of longstanding questions about the identity of these Hawaiian Cassiopea, Holland et al. (2004) undertook a broad genetic survey of Cassiopea from across its distribution. To their surprise, they found deep mtDNA sequence divergence between different samples that were supposedly C. andromeda, suggesting the presence of cryptic (i.e., unrecognized) species. Conversely, some geographically distant samples (even of putatively different species, such as Hawaii C. andromeda and Bermuda and Florida Keys C. xamachana) showed surprisingly little genetic difference, suggesting that they were actually representatives of the same species that had dispersed enormous distances in modern times (presumably with inadvertent assistance from humans). An important genetic result that was consistent with pre-existing species concepts based on morphology was the finding that sequences from Panama and Florida Keys C. frondosa were very different from other Cassiopea sequences (including C. xamachana, with which it co-occurs) but similar to one another, suggesting that C. frondosa is indeed a distinct species. Currently available data appear to support at least two independent introductions to the Hawaiian Islands, one from the Indo-Pacific and another from the western Atlantic/Red Sea (Holland et al. 2004).

Because their study was based on a single genetic marker (mitochondrial DNA) and involved limited sampling, Holland et al. emphasize that it would be premature to formally revise the taxonomy of Cassiopea. Nevertheless, the molecular phylogenetic results of Holland et al. (2004) tentatively support six species: (1) C. frondosa, sampled from the western Atlantic; (2) C. andromeda sampled from the Red Sea, western Atlantic, and Hawaiian Islands; (3) a species for which the authors propose reviving the old name C. ornata, sampled from Indonesia, Palau, and Fiji; (4) a species for which the authors use the provisional name Cassiopea sp. 1, sampled from eastern Australia (5) a species for which the authors use the provisional name Cassiopea sp. 2, sampled from Papua New Guinea; and (6) a species for which the authors use the provisional name Cassiopea sp. 3, sampled from Papua New Guinea and the Hawaiian Islands. Some of these samples clearly represent human-assisted introductions (Holland et al. 2004).

Medusae obtain a portion of their carbon requirements from symbiotic dinoflagellate algae of the genus Symbiodinium, also known by the general term ‘‘zooxanthellae’’. In contrast to zooxanthellate corals, only the largest Cassiopea are theoretically able to obtain all of the carbon necessary to fuel their respiratory metabolism from their zooxanthellae (Vodenichar, 1995, cited in Fitt and Costley 1998), and most medusae must obtain a portion of their nutrients from external feeding and possibly from absorption of dissolved nutrients.

Cassiopea are carnivorous. Larson (1997) studied the feeding behaviour of Cassiopea frondosa and "C. xamachana". These jellyfish filter prey from the water with the pumping activity of the bell. Prey, mainly small epibenthic crustaceans (0.2-10 mm in length), are caught mostly by interception. However, some prey may contact the oral surface as a result of turbulence or by their own locomotion. Larson found that prey capture was essentially the same for both species, except that the vesicles take an active part in prey capture only in C. frondosa. Ingestion occurred after the digitate-fringed lips of the funnel-shaped oral ostia opened. The digitata with attached prey then bent inward towards the ostium and prey are swept into the ostium, and transported to the stomach by ciliary activity. Prey items were similar for both medusae. Copepods, chiefly harpacticoids, with fewer cyclopoid and calanoid species, were most numerous; ostracods were second in numerical abundance, followed by tanaids and chironomids. Other prey consisted of gammaroids, nematodes, mysids, miscellaneous eggs, veligers, chaetognaths, cumaceans, foraminifera, and others. On a weight basis, harpacticoid copepods, tanaids, and chironomids made up around 30% each, followed by mysids at around 10%.

Dieser Artikel behandelt eine Gattung der Schirmquallen. Für die mythische Figur siehe Kassiopeia (Mythologie), für das Sternbild Kassiopeia (Sternbild).

Cassiopea (auch: Mangrovenqualle) ist eine Gattung der Schirmquallen. Diese Quallen sind weltweit zu finden und leben häufig – aber nicht ausschließlich – in seichten, von Mangroven geprägten Küstengewässern. Dort halten sie sich bevorzugt auf sandigen oder von Seegras bewachsenen Flächen auf. Meistens trifft man sie in größeren Gruppen an.

Cassiopea sp. in seaweed.

Cassiopea (upside-down jellyfish) is a genus of true jellyfish and the only members of the family Cassiopeidae. They are found in warmer coastal regions around the world, including shallow mangrove swamps, mudflats, canals, and turtle grass flats in Florida, and the Caribbean and Micronesia. The medusa usually lives upside-down on the bottom, which has earned them the common name. These jellyfish partake in a symbiotic relationship with photosynthetic dinoflagellates and therefore, must lie upside-down in areas with sufficient light penetration to fuel their energy source. Where found, there may be numerous individuals with varying shades of white, blue, green and brown.

Cassiopea, comúnmente llamadas "medusas invertidas", es un género de medusas, pertenecientes a la familia Cassiopeidae, al orden Rhizostomeae y a la clase Scyphozoa. Pueden encontrarse en áreas costeras cálidas de todo el planeta, incluyendo zonas de manglares.​

Le genre Cassiopea, aussi appelé Cassiopeia, est un genre de méduses de la famille des Cassiopeidae, de l'ordre Rhizostomeae et de la classe des Scyphozoa.

Cassiopea Péron & Lesueur, 1809 è un genere di meduse, unico genere appartenente alla famiglia Cassiopeidae.

Questi animali, differentemente dalle meduse più note, vivono adagiate sul fondale marino con la bocca e i tentacoli rivolti verso l'alto. In questo modo le alghe simbionti che vivono nei tessuti dei tentacoli, sono esposti alla luce e possono compiere la fotosintesi.

Cassiopea is het enige geslacht van Cassiopeidae, een familie van schijfkwallen.