Octopus, cuttlefish and squid, and most of the group is octopus. Soft ground suits them: an animal with no shell and no bones needs a hole, a shell or a burrow rather than a reef, and a silt slope offers all three. The exception is the chambered nautilus, which carries its own shell and is met over deep water rather than on the bottom.
The daylight animals are the ones a guide will find on a first dive. The coconut octopus carries half a shell across open sand and is among the most reliably found animals on silt; the small sand cuttlefish sit with skin flaps raised over the eyes; the day octopus hunts in the open and changes pattern several times a minute. The rest are worked for. The mimic octopus and the wunderpus are animals of rubble edges at dawn and dusk, and are separated on markings rather than on behaviour. The blue-ringed and mototi octopuses live in bottles, shells and crevices in the shallows and show their colours only when they are disturbed, which is an argument for not disturbing them.
After dark the group changes. Bobtail and bottletail squid come up out of the sand they spent the day buried in, the ornate and starry night octopuses hunt in the open, and the pygmy squid, two centimetres long and glued to the underside of a weed blade, is found by searching the weed rather than the ground.
The hardest entries here are the hairy octopus, undescribed and thumbnail-sized, usually taken for a scrap of algae, and the animals that arrive with the water rather than living on the bottom at all: the two argonauts, whose females drift in a thin case built by two of their own arms, and the chambered nautilus, recorded here only from Papua New Guinea. Records for all of them are thin, and the ratings say so.
Every one has a page. They are shown as a list rather than as pictures because nothing has been photographed or logged for them yet, and a species with nothing behind it should not sit in front of one that has.
How many of the 36 carry a record at each destination. A species usually carries several, so these do not add up to 36.
All 1316 species in one index, with filters for destination, rarity and hazard.
