''Cassiopea xamachana'', commonly known as the upside-down jellyfish, is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

jellyfish Jellyfish, also known as sea jellies or simply jellies, are the #Life cycle, medusa-phase of certain gelatinous members of the subphylum Medusozoa, which is a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animal ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Cassiopeidae. It is found in warm parts of the western

Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

, the

Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...

, and the

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

. It was first described by the American marine biologist

Henry Bryant Bigelow Henry Bryant Bigelow (October 3, 1879 – December 11, 1967) was an American oceanographer and marine biologist. He was a professor at Harvard University for 60 years and was the founding director of the Woods Hole Oceanographic Institution. Th ...

in 1892.

Description

The

medusa In Greek mythology, Medusa (; ), also called Gorgo () or the Gorgon, was one of the three Gorgons. Medusa is generally described as a woman with living snakes in place of hair; her appearance was so hideous that anyone who looked upon her wa ...

phase of ''Cassiopea xamachana'' can grow to a diameter of about . Compared to most species of jellyfish it is upside-down, that is to say the bell, which is saucer-shaped, is underneath and acts like a suction cup to stabilise the jellyfish on the seabed. The four pairs of much-branched tentacles are on the upperside. Instead of a central mouth, there are numerous oral openings in the tentacles which connect via channels to the stomach. The

mesogloea Mesoglea refers to the extracellular matrix found in cnidarians like coral or jellyfish as well as ctenophores that functions as a hydrostatic skeleton. It is related to but distinct from mesohyl, which generally refers to extracellular material f ...

, the jelly-like tissue, contains

symbiotic Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...

zooxanthellae Zooxanthellae (; zooxanthella) is a colloquial term for single-celled photosynthetic organisms that are able to live in symbiosis with diverse marine invertebrates including corals, jellyfish, demosponges, and nudibranchs. Most known zooxanthell ...

, single-celled

protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...

s, which are

photosynthetic Photosynthesis ( ) is a Biological system, system of biological processes by which Photoautotrophism, photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical ener ...

and give the jellyfish its variable color, often bluish-grey or bluish-green.

Distribution and habitat

''Cassiopea xamachana'' is found in warm parts of the western Atlantic Ocean, the Caribbean Sea and the Gulf of Mexico. It is normally found in large aggregations on the muddy seabed of inshore bays and shallow lagoons. If disturbed the jellyfish may pulsate their bells and rise in the water, soon flopping back onto the seabed.

Biology

''Cassiopea xamachana'' obtains part of its nutritional needs from the

photosymbiotic Photosymbiosis is a type of symbiosis where one of the organisms is capable of photosynthesis. Examples of photosymbiotic relationships include those in lichens, plankton, ciliates, and many marine organisms including corals, fire corals, giant ...

it harbors in its tissues; these use energy from the sunlight to produce carbohydrates by photosynthesis. For its further needs, as well as being able to absorb nutrients dissolved in the water, it can also catch small prey using the

cnidocyte A cnidocyte (also known as a cnidoblast) is a type of cell containing a large secretory organelle called a ''cnidocyst'', that can deliver a sting to other organisms as a way to capture prey and defend against predators. A cnidocyte explosively ...

s with which its tentacles are armed. Having paralysed the

prey Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not ki ...

, it digests them on the oral surfaces and the resulting fragments are ingested through the oral openings. This species has become an important model system to study the molecular basis of cnidarian-algal symbiosis. The life cycle of ''Cassiopea xamachana'' alternates between a polyp phase and the medusa phase. Gametes are released by the medusae into the water and the fertilized eggs hatch into

planula A planula is the free-swimming, flattened, ciliated, bilaterally symmetric larval form of various cnidarian species and also in some species of Ctenophores, which are not related to cnidarians at all. Some groups of Nemerteans also produce larva ...

larvae, which attach to the sea bed or some other suitable

substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached ** Substrate (aquatic environment), the earthy material that exi ...

. Decomposing

red mangrove Red mangrove may refer to at least three plant species: * ''Rhizophora mangle'' * ''Rhizophora mucronata ''Rhizophora mucronata'' (loop-root mangrove, red mangrove or Asiatic mangrove) is a species of mangrove found on coasts and river banks in E ...

(''Rhizophora mangle'') give off a substance which attracts the larvae to settle. Having settled, the larvae undergo

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and different ...

into the hydroid stage of the lifecycle, forming tiny sessile polyps called scyphistomae. Under favorable conditions these bud and form further scyphistomae. In due course, when they have acquired zooxanthellae and the temperature exceeds , these strobilate (split) and new medusae are formed. In Florida, the medusae are found all the year round but the scyphistomae are only present in late summer and fall. This is the reverse of the usual situation of rhizostome jellyfish, in more temperate locations, where the scyphistomae are temperature-tolerant and the medusae are cold-sensitive. The jellyfish surround themselves with a layer of

mucus Mucus (, ) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both Serous fluid, serous and muc ...

containing cassiosomes, independent bodies consisting of a layer of stinging cells surrounding a piece of jelly as described in a 2020 study featuring notable scientists such as Jennie Janssen. Between sixty and a hundred

cilia The cilium (: cilia; ; in Medieval Latin and in anatomy, ''cilium'') is a short hair-like membrane protrusion from many types of eukaryotic cell. (Cilia are absent in bacteria and archaea.) The cilium has the shape of a slender threadlike proj ...

enable the cassiophore to swim independently of the jellyfish's body. The cassiophores allow the jellyfish to kill or stun its prey at a distance, and are responsible for the stinging sensation experienced by swimmers, divers and aquarists who get too close to the jellyfish.

Etymology

In Greek mythology,

Cassiopeia Cassiopeia or Cassiopea may refer to: Greek mythology * Cassiopeia (mother of Andromeda), queen of Aethiopia and mother of Andromeda * Cassiopeia (wife of Phoenix), wife of Phoenix, king of Phoenicia * Cassiopeia, wife of Epaphus, king of Egy ...

was the mother of Andromeda. Cassiopeia was punished by

Poseidon Poseidon (; ) is one of the twelve Olympians in ancient Greek religion and mythology, presiding over the sea, storms, earthquakes and horses.Burkert 1985pp. 136–139 He was the protector of seafarers and the guardian of many Hellenic cit ...

, ruling god of the sea, for being a bad mother. The specific epithet, xamachana, was chosen by Bigelow to honor the indigenous name of the island of Jamaica, the type location of the species.Bigelow, R.P. (1892). On a new species of ''Cassiopea'' from Jamaica. ''Zoologischer Anzeiger''. 15: 212-214. Bigelow collected the specimen in a lagoon near Kingston Harbor, Jamaica.

References

External links

* {{Taxonbar, from=Q2607889 xamachana Cnidarians of the Atlantic Ocean Cnidarians of the Caribbean Sea Animals described in 1892 Taxa named by Henry Bryant Bigelow