Ranina ranina, also known as the Huỳnh Đế crab,(red) frog crab or spanner crab, is a species of crab found throughout tropical and subtropicalhabitats. It is often fished for its meat, and is the only known species in its genus.
It may grow up to 150 millimetres (5.9 in) long, and may weigh up to 900 grams (2.0 lb). The carapace is wider at the front, reddish brown in color, with ten white spots.Ranina ranina is mainly nocturnal, and remains buried in the sand during the day.Ranina ranina is easily distinguished from other crab species in its habitat due to its red carapace and elongated midsection.
Spanner crabs inhabit coastal waters along the east coast of Australia, from Yeppoon in Queensland to the North coast of New South Wales. There is also a population to the north of Perth in Western Australia.Ranina ranina is abundant in the coastal waters of south-western Mindanao, Philippines. These crabs are also found in the eastern coast of Africa, across the Indian Ocean to Indonesia, Japan and Hawaii and Vietnam.
Ranina ranina inhabits depths of 10–100 metres (33–328 ft) on sandy-smooth substrata in which they bury themselves from where they attack small bottom-dwelling fish. When waiting for prey, Ranina ranina will cover itself with sand, but leave its eye and mouthparts sticking out to help detect its food. Offshore areas within this range in a subtropical or tropical environment serves as a habitat for Ranina ranina, but they must have ample sand for Ranina ranina to flourish, as covering themselves in sand is instrumental in their method of catching prey.