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Species of jellyfish

Phacellophora camtschatica, commonly known as the fried egg jellyfish or egg yolk jellyfish, is a very large jellyfish in the family Phacellophoridae. This species 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, 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). 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, P. camtschatica 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. Tentacles contain nematocysts, 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 camtschatica 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.

Phacellophora camtschatica 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.

Phacellophora camtschatica does not have respiratory organs such as gills, lungs or trachea. Instead, it respires by diffusing 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 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, and circulatory systems because of the high surface area to volume ratio. The basic body plan consists of several parts. Food travels through the muscular manubrium 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, which in this phylum is replaced with mesoglea. The tissue layers of this species is a middle layer of mesoglea, a gastrodervascular cavity with a gastrodermis, and an epidermis. Additionally, there is a nerve net that is responsible for contractions in swimming muscles and responses while feeding. Cnidarians 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.

The life cycle of this jellyfish is well known, because it is kept in culture at the Monterey Bay Aquarium. During its life cycle, it alternates between an asexual benthic 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 planulae 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. 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.