Postcard from the Reef – The Horn of Urchin Death

Horned helmet snails feed on sea urchins. The snails are easy to spot once you know what to look for, a shape in the sand. The snail may appear like an abandoned shell on first examination, the top covered with algae. It is the size that is surprising, these snails are huge, the shell well over a foot long and almost as much in diameter.

If an urchin wanders by this snail comes to life, heaving itself out of the sand and moving towards its prey. The large foot appears, lifting the ponderous mass off the ground. A pair of tentacles with small black eyes on the sides appear, sweeping about to search for prey. Once the urchin is located the reaction is surprisingly swift, the snail heaves forward to engulf the hapless urchin.

Horned Helmet Snail
Horned helmet snail (Cassis cornuta) pouncing on a collector urchin (Tripneustes gratilla)

Postcard from the Reef – Urchin Crab

Sometimes it is simply knowing where to look.

I have known about these guys for a while, even looked a few times. It is daunting when you know exactly where to look, but that place is heavily defended and tough to approach. Obtaining a photo of something that is nestled amongst six inch spines? Challenging…

Sea Urchin Crab
A female sea urchin crab (Echinoecus pentagonus) in the anal cavity of a large banded urchin (Echinothrix calamaris)

Postcard from the Reef – Helmet Urchin

They are everywhere in the tide zone, an extraordinarily common species. So common I usually forget to take a picture. A closer look shows a cool animal. The spines are modified, no sharp needles here, armor plates instead. An excellent arrangement for resisting the fury of the waves and still giving protection from would be predators.

Helmet Urchin
Helmet urchin (Colobocentrotus atratus) in the tidal zona at O'oma