Greater blue-ringed octopus

Hapalochlaena lunulata, the greater blue-ringed octopus (Octopodidae), is a small species with a mantle about 5 cm long, a total length near 10 cm and a mean weight of about 80 g. Some 60 electric-blue rings, 7–8 mm across and outlined in black, flash within about one-third of a second when the animal is alarmed. It inhabits coral reefs, rubble, sand and seagrass from the intertidal zone to about 20 m across the Indo-West Pacific. It takes small crabs, hermit crabs, shrimps and gastropods, paralysing them with tetrodotoxin from its posterior salivary glands. IUCN rated it Least Concern in 2018.