page_title: Flower hat jelly
section_title: Appearance and life cycle
hierarchical_section_title: Flower hat jelly / Appearance and life cycle
caption_attribution_description: Flower hat jelly (Olindias formosa) under blacklight at Monterey Bay Aquarium.
context_page_description: The flower hat jelly is a species of hydrozoan in the family Olindiidae. Although they look like a jellyfish, they actually belong in the class Hydrozoa, while true jellyfish belong in class Scyphozoa. Flower hat jellies occur in the northwestern Pacific off central and southern Japan, and South Korea's Jeju Island. 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.
  The sting of the flower hat jelly is generally mildly painful and leaves a rash. There is a single known human fatality from Japan.
context_section_description: This fluorescent jelly has lustrous tentacles 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 15 cm (6 in) in diameter. When first observed in the wild, typically around December, they only measure 2 cm (0.8 in).
  Little is known about the details of its life cycle and no Olindias hydroids have been reported from the wild. Flower hat jellies have bred in a display at the Monterey Bay Aquarium. The hydroids attached themselves to various surfaces and formed small clusters. Eventually the medusae were released at a diameter of about 1 mm (0.04 in). Budding only happened when the hydroids were kept at water temperatures of 15 °C (59 °F); not 20 °C (68 °F) or 25 °C (77 °F). In contrast, the two warmer temperatures appeared to produce more medusae. This indicates that hydroid growth and reproduction (budding) occur in 15 °C (59 °F) 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 15–18 °C (59–64 °F).
caption: A flower hat jelly with its tentacles extended under blacklight
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