The flower hat jelly (''Olindias formosus'') is a species of

hydromedusa ''Hydromedusa'' is a turtle genus in the family Chelidae, commonly known as the South American snake-necked turtles. They are quite closely related to the South American side-necked swamp turtles (''Acanthochelys'') and the snake-necked turtles ...

in the hydrozoan family

Olindiidae Olindiidae is a family of hydrozoans in the order Limnomedusae. They have a polyp (zoology), polyp phase and a Jellyfish, medusa phase. The polyps are generally small (1 mm) and solitary, but a few species are colonial. They have a varying ...

. Although they look like a

jellyfish Jellyfish and sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella- ...

, they actually belong in the class

Hydrozoa Hydrozoa (hydrozoans; ) are a taxonomic class of individually very small, predatory animals, some solitary and some colonial, most of which inhabit saline water. The colonies of the colonial species can be large, and in some cases the specializ ...

, while true jellyfish belong in 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 ...

. Flower hat jellies occur in the northwestern Pacific off central and southern Japan, and South Korea's Jeju Island.Patry, W.; T. Knowles; L. Christianson; M. Howard (2014). The hydroid and early medusa stage of Olindias formosus (Cnidaria, Hydrozoa, Limnomedusae). Journal of the Marine Biological Association of the United Kingdom 94(7): 1409–1415. (close relatives live elsewhere, like '' O. sambaquiensis'' found off Argentina and Brazil).Resgalla Junior, C.; A.L. Rosseto; V. Haddad Jr (2011). Report of an outbreak of stings caused by Olindias sambaquiensis Muller, 1861 (Cnidaria: hydrozoa) in Southern Brazil. Braz. j. oceanogr. 59(4). The adult form of the flower hat jelly only lives a few months and is typically seen from December to July, with peaks in April and May. During the day they rest on the bottom, often among rocks or algae, but at night they float up to hunt for their prey, typically small fish.Monterey Bay Aquarium
Flower hat jelly
Retrieved 17 March 2019. The sting of the flower hat jelly is generally mildly painful and leaves a rash. There is a single known human fatality from Japan.

Appearance and life cycle

Flower Hat Jelly Monterrey Bay Aquarium 2015

This fluorescent jelly has lustrous

tentacle In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work main ...

s that coil and adhere to its rim when not in use. Its bell is translucent and pinstriped with opaque bands. The flower hat jelly can grow to be about in diameter. When first observed in the wild, typically around December, they only measure . Little is known about the details of its life cycle and no '' Olindias''

hydroids Hydroids are a life stage for most animals of the class Hydrozoa, small predators related to jellyfish. Some hydroids such as the freshwater '' Hydra'' are solitary, with the polyp attached directly to the substrate. When these produce buds ...

have been reported from the wild. Flower hat jellies have bred in a display at the

Monterey Bay Aquarium Monterey Bay Aquarium is a 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 October 1984. Its biologists ...

. The hydroids attached themselves to various surfaces and formed small clusters. Eventually the medusae were released at a diameter of about .

Budding Budding or blastogenesis is a type of asexual reproduction in which a new organism develops from an outgrowth or bud due to cell division at one particular site. For example, the small bulb-like projection coming out from the yeast cell is know ...

only happened when the hydroids were kept at water temperatures of ; not or . In contrast, the two warmer temperatures appeared to produce more medusae. This indicates that hydroid growth and reproduction (budding) occur in or less, while warmer temperatures initiate the change into medusae. This matches the annual sea temperature variations observed in its native range. In aquariums, adults are usually kept in full salt water that is about .

References

Olindiidae Animals described in 1903 {{hydrozoa-stub