Ramose Murex

A heavy, frilled shell up to 33 cm (13 in), one of the largest murexes anywhere. Three ribs on each whorl carry rows of hollow leaf-shaped fronds that curl backward, and the whole thing is usually so crusted with algae and worm tubes that the animal looks like a lump of reef until it moves. The aperture underneath is clean white flushed with pink.

The fronds are armor with a second job. They make the shell awkward for a crab or a fish to get a grip on, and they act as a stand: dropped on soft sand the shell tends to land aperture-down, which is the position the snail wants. Every time growth pauses, the mantle builds a new set and the old ones stay behind as a record of the animal's growth stops.

It is a driller. Muricids hunt clams, oysters and other snails, and this one works through the prey's shell with a combination of rasping and chemistry: the radula grinds while a gland in the foot secretes acid and enzymes that soften the calcium carbonate underneath. A large bivalve can take the better part of a day to open. The neat round holes in beach shells, drilled at exactly the point above the prey's muscle, are the signature of this family.

The family also made purple. Muricids carry a gland that produces a colorless fluid which turns violet in sunlight, and that reaction was the basis of Tyrian purple, the dye that colored imperial Rome and cost more than its weight in silver. This species is one of the Indo-Pacific relatives put to the same use, and along the Indian coast it is fished on a commercial scale for its meat, its shell and its lime.

Which is why big ones are getting hard to find. The shell is a standard souvenir and the animal is edible, so collecting takes the largest individuals first, exactly the ones producing the most eggs. Females gather to lay in communal masses of horny capsules stuck to rock, sometimes hundreds of animals at a site, which makes a breeding aggregation easy to strip in a single visit.