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''Phacellophora'', commonly known as the fried egg jellyfish or egg-yolk jellyfish, is a very large
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 monotypic family Phacellophoridae containing a single species ''Phacellophora camtschatica''. This genus can be easily identified by the yellow coloration in the center of its body which closely resembles an egg yolk, hence its common name. Some individuals can have a bell close to 60 cm (2 ft) in diameter, and most individuals have 16 clusters of up to a few dozen tentacles, each up to 6 m (20 ft) long. A smaller jellyfish, ''
Cotylorhiza tuberculata ''Cotylorhiza tuberculata'' is a species of jellyfish of the phylum Cnidaria, also known as the Mediterranean jellyfish, Mediterranean jelly, or fried egg jellyfish. It is commonly found in the Mediterranean Sea, Aegean Sea, and Adriatic Sea. De ...
'', typically found in warmer water, particularly in the Mediterranean Sea, is also popularly called a fried egg jellyfish. Also, ''P. camtschatica'' is sometimes confused with the Lion's mane jellyfish (''
Cyanea capillata The lion's mane jellyfish (''Cyanea capillata'') is one of the Largest organisms#Cnidarians (Cnidaria), largest known species of jellyfish. Its range is confined to cold, boreal ecosystem, boreal waters of the Arctic Ocean, Arctic, northern Atla ...
''). It feeds primarily by collecting
medusae Jellyfish, also known as sea jellies or simply jellies, are the 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 animals, althoug ...
and
plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...
with its tentacles, and bringing them into its mouth for digestion. It is capable of only limited motion, and mostly drifts with the current, even when swimming. This species and most of its relatives in the Cnidaria phylum often use suspension feeding as their main food gathering strategy. The body of this jellyfish does not contain any respiratory, circulatory, or excretory systems. Instead, it uses its large surface area to accomplish these things. Also, this species (and all others in the phylum
cnidaria Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...
) lack a mesoderm and instead uses mesoglea. Therefore, there are not three true tissue layers, in turn making this species (and all other cnidarians) diploblastic, not triploblastic. The reproduction and life cycle of this jellyfish has been well documented. It mostly follows the same life cycle as other members in the class
Scyphozoa The Scyphozoa are an exclusively marine class of the phylum Cnidaria, referred to as the true jellyfish (or "true jellies"). The class name Scyphozoa comes from the Greek word '' skyphos'' (), denoting a kind of drinking cup and alluding to the ...
. It alternates between a polyp form that reproduces asexually and a medusa form that reproduces sexually. These jellyfish are a cool water species found in most of the world’s oceans, but most commonly in the Northern Pacific.


Taxonomy and systematics

''Phacellophora'' has only one species, ''P. camtschatica''. ''P. camtschatica'' is a large jellyfish that has a yellow center, resembling a broken egg yolk, surrounded by opaque, white tissue. This jellyfish is the representative of the family Phacellophoridae in the class of
Scyphozoa The Scyphozoa are an exclusively marine class of the phylum Cnidaria, referred to as the true jellyfish (or "true jellies"). The class name Scyphozoa comes from the Greek word '' skyphos'' (), denoting a kind of drinking cup and alluding to the ...
.This jellyfish was once believed to be part of the family, Ulmaridae, but the juvenile characteristics did not match the family characteristics of
Ulmaridae The Ulmaridae are a family of jellyfish, which includes the famous moon jellies, and other jellyfish with unique characteristics like '' Tiburonia granrojo''. Genera Formerly, the genus '' Phacellophora'' was also included in this family, but ...
or
Cyaneidae The Cyaneidae are a family of true jellyfish. About 20 species are in this family, including the well-known lion's mane jellyfish, lion's-mane jellyfish. Species The following species are recognized within the family Cyaneidae. Formerly, this f ...
. Due to these findings, the family Phacellophoridae was created specifically for this genus, serving as an intermediate between Cyaneidae and Ulmaridae. Key distinguishing features are a gastric cavity with radial canals joining a marginal ring canal, as well as broad curtain-like oral arms; and subumbrellar tentacles in 16 linear clusters. Currently, ''Phacellophora'' is the sole member of the family Phacellophoridae. However, the latest phylogenetic analyses actually suggest the genus ''Phacellophora'' is a member of the family Ulmaridae. Furthermore, cryptic diversity is evident within the genus ''Phacellophora'', with at least three or four distinct species.


Ecology


Feeding

''Phacellophora'' mainly feeds on gelatinous zooplankton and smaller jellyfish, which become ensnared within the tentacles. Tentacles contain
nematocysts 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 ...
, which help in prey capture. These structures also provide defense against predation. Food that is caught in the tentacles is then covered in mucous, then these tentacles are brought to the mouth by oral lobes. Food is then digested by digestive enzymes in the gastrovascular cavity. Broken-down food is then distributed throughout the jellyfish by ciliary action. ''Phacellophora'' feeds on a great variety of taxa, including euphausiids, cladocerans, and decapod zoea, fish (including fish larvae), and especially other jellyfish such as '' Aurelia'' spp., ctenophores and ''
Pelagia noctiluca ''Pelagia noctiluca'' is a jellyfish in the family Pelagiidae and the only currently recognized species in the genus ''Pelagia''. It is typically known in English as the mauve stinger, but other common names are purple-striped jelly (causing pot ...
''. The fried egg jellyfish have been known to host symbionts that will transfer onto ''Phacellophora'' when the host is consumed. This is possible because the sting of this jellyfish is weak therefore allowing many symbionts/parasites including small crustaceans like larval crabs ('' Cancer gracilis'') and some
Amphipoda Amphipoda () is an order (biology), order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods () range in size from and are mostly detritivores or scavengers. There are more than 10,700 amphip ...
(''
Hyperia medusarum ''Hyperia'' is a genus of amphipods 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 ...
'') to regularly ride on its bell and even steal food from its oral arms and tentacles.


Symbiotic Relationships

''Phacellophora'' has symbiotic relationships with larval crabs (''Cancer gracilis),'' in which the crabs feed on the parasitoid Amphipoda (''Hyperia medusarum)'' that also resides on the bell of the jellyfish. Larval crabs benefit from this relationship by riding on the bell of the medusa or within the tentacles to gain food and develop faster due to locomotion through warmer surface waters without expending extra energy. When the juvenile crabs first associate with the jellyfish, the crab feeds on the tentacles and preys on small plankton from the water and the hosts’ surface. As the crab develops into an instar, it begins to feed on the parasitoid Amphipoda (''Hyperia medusarum)'', which aids the jellyfish in keeping the parasitic impact low''.'' Although a symbiotic relationship exists between juvenile ''Cancer gracilis'' and the jellyfish, when the ''C. gracilis'' matures it begins to feed more substantially on the jellyfish itself; other predators include crabs (''
Cancer productus ''Cancer productus'', one of several species known as red rock crabs, is a crab of the genus ''Cancer'' found on the western coast of North America. This species is commonly nicknamed the Pearl of the Pacific Northwest. Description ''Cancer p ...
'' and ''
Pugettia producta ''Pugettia producta'', known as the northern kelp crab or shield-backed kelp crab, is a species of crab in the family Epialtidae. Description Its upper carapace is typically dark brown, olive, or olive-brown. The underside surface tends to be ...
)'' and the giant deep-sea octopus, ''
Haliphron atlanticus The seven-arm octopus (''Haliphron atlanticus''), also known as the blob octopus or sometimes called septopus, is one of the two largest known species of octopus; the largest specimen ever discovered had an estimated total length of and mass o ...
'', which clings to the jellyfish and consumes its oral arms and stomach.


Body systems

''Phacellophora'' does not have
respiratory The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies gr ...
organs such as
gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...
s,
lung The lungs are the primary Organ (biology), organs of the respiratory system in many animals, including humans. In mammals and most other tetrapods, two lungs are located near the Vertebral column, backbone on either side of the heart. Their ...
s or
trachea The trachea (: tracheae or tracheas), also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all animals' lungs. The trachea extends from ...
. Instead, it respires by
diffusing Molecular diffusion is the motion of atoms, molecules, or other particles of a gas or liquid at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid, size and density (or their product, ...
oxygen from water through the thin membrane covering its body. Within the gastrovascular cavity, low oxygenated water can be expelled through the mouth and high oxygenated water can be distributed by
ciliated 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 pr ...
action, thus increasing the diffusion of oxygen into the cells. The large surface area to volume ratio helps to diffuse more oxygen and nutrients into the cells. Similarly, this animal lacks dedicated respiratory,
excretory Excretion is elimination of metabolic waste, which is an essential process in all organisms. In vertebrates, this is primarily carried out by the lungs, kidneys, and skin. This is in contrast with secretion, where the substance may have specific ...
, and
circulatory system In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart ...
s because of the high surface area to volume ratio. The basic body plan consists of several parts. Food travels through the muscular
manubrium The sternum (: sternums or sterna) or breastbone is a long flat bone located in the central part of the chest. It connects to the ribs via cartilage and forms the front of the rib cage, thus helping to protect the heart, human lung, lungs, and ma ...
while the radial canals help disperse the food. The fried egg jelly and all other members of the phylum Cnidaria are diploblastic. This is due to a lack of a
mesoderm The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical ...
, which in this phylum is replaced with
mesoglea 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 tissue layers of this species is a middle layer of
mesoglea 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 ...
, a gastrodervascular cavity with a
gastrodermis Gastrodermis (from Ancient Greek: , , "stomach"; , , "skin") is the inner layer of Cell (biology), cells that serves as a lining membrane of the gastrovascular cavity in cnidarians. It is distinct from the outer epidermis and the inner dermis and ...
, and an
epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermal layer provides a barrier to infection from environmental pathogens and regulates the ...
. Additionally, there is a
nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...
net that is responsible for contractions in swimming muscles and responses while feeding.
Cnidaria Cnidaria ( ) is a phylum under kingdom Animalia containing over 11,000 species of aquatic invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...
ns have radial symmetry, in which tentacles are radially symmetric about the mouth, and have two main body surfaces, an oral surface and an aboral surface. During polyp stage, the oral surface is oriented upwards, but during medusa stage the oral surface is oriented downwards for more efficient mobility.


Life Cycle

The life cycle of this jellyfish is well known, because it is kept in culture at the
Monterey Bay Aquarium Monterey Bay Aquarium is a Nonprofit organization, nonprofit public aquarium in Monterey, California. Known for its regional focus on the marine habitats of Monterey Bay, it was the first to exhibit a living kelp forest when it opened in Octob ...
. During its life cycle, it alternates between an asexual
benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...
polyp stage attached to rocks and piers and a sexual planktonic medusa stage that reproduces in the water column; both males and females occur in the plankton form. The life cycle begins by eggs being fertilized, then developing 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 ...
e that are covered in cilia. These planulae swim for roughly 3–5 days before settling by attaching to the bottom and transforming, or metamorphosing, into the polyp (scyphistomae) stage. Once in the polyp stage, the scyphistomae undergoes a series of 2-, 4-, 8-, and 16- tentacled stages of development, each representing a difference in the overall shape of the calyx and symmetry amongst tentacles. When the polyp is mature, with 30–44 tentacles present, asexual proliferation occurs via side budding, one bud per polyp, and strobilating. During strobilation, the polyp is lengthened and thinned while tentacles are shortened and thickened, and mature ephraye are released. When ephyrae are released, a cruciform mouth is present with
nematocyst 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 ...
batteries scattered throughout. As ephraye mature, the tentacles elongate and become filiform. Medusae reach larger bell diameters, additional tentacles form and oral arms elongate. Gastric system develops in a centrifugal direction. After roughly 9 months (under laboratory conditions), sexual maturity is achieved and reproduction can be achieved within the water column. The cycle then repeats all over again.


Distribution

This cool-water genus are found in many parts of the world's oceans even though the abundance of the sole species in open marine waters is relatively low. Though, it can be rather abundant in some parts of the Sea of Japan and the Sea of Okhotsk, especially near the shore where it was found to dominate in the southern part of this area. However, most individuals are found in isolation. It was also found in the western and eastern Bering Sea. Additionally, it constituted a noticeable proportion of jellyfish biomass in waters of the northern California Current. In a study conducted in 2011, the egg-yolk jelly was found to aggregate mostly over deep basins, whereas in shallow areas a significant quantity of this species was found only off West Kamchatka, This is in stark contrast to the other members of the family Ulmaridae (since it is no longer a member) which prefer shallow water. This preference could be related to the bell size of the individual which ranges from 5–59 cm. This bell size likely allows the jellyfish to swim in deeper waters by resisting stronger water currents and pressure. Also, jellyfish populations (including the egg-yolk jelly) are on the rise in degraded areas as a result of increased tolerance to detrimental factors. Additionally, jellyfish play a large role in the food web and can serve as indicators of ecosystem structure and function; The larger the jellyfish population, the greater the negative impact on
ecosystem service Ecosystem services are the various benefits that humans derive from ecosystems. The interconnected living and non-living components of the natural environment offer benefits such as pollination of crops, clean air and water, decomposition of wast ...
s. The fried egg jellyfish typically moves faster during the day and swims fastest during flood tides. This jellyfish undergoes vertical migrations that span the water column throughout short and long time frames. These vertical migrations allow them to enter the low depth of the hypoxia zone. This genus typically resides below the
pycnocline A pycnocline is the cline or layer where the density gradient () is greatest within a body of water. An ocean current is generated by the forces such as breaking waves, temperature and salinity differences, wind, Coriolis effect, and tides caused ...
and avoids crossing the boundary layer, but they often dive into the hypoxic layer during the day when competition is high. By diving deep into the hypoxia zone, the fried egg jellyfish evades competition; unlike other species where hypoxia generally causes species to move away from the oxygen depleted zone, the fried egg jellyfish is able to withstand low oxygen levels for several hours at a time. And, with the belief that hypoxia regions will continue to grow, the fried egg jellyfish could thrive.


References


External links


Image of ''Phacellophora camtschatica''
{{Taxonbar, from=Q2352335 Semaeostomeae Taxa described in 1835 Taxa named by Johann Friedrich von Brandt Cnidarians of the Pacific Ocean