Zombies of the Reef

Every night, at feeding time, my little reef has a moment reminiscent of “Night of the Living Dead.”

My “clean up crew” includes several types of aquatic snails., among them Nassarius (Nassarius sp.), a largely carnivorous scavenging snail that feeds on dead things–and leftover fish food.

14A14 Nassarius 1

Nassarius (known in the UK as “dog whelks”) spend most of their time buried in the sand. Their regular burying stirs and aerates the sand bed, which is good for the aquarium’s general health. They’re also good at vacuuming up any leftover food and detritus, using a long, retractable proboscis that looks a lot like the siphon they use to breathe.

14A14 Nassarius 2 (closeup)

The extension visible here is the snail’s siphon – which it uses as a combination breathing tube and scent organ. The feeding tube looks similar, when extended.

When buried in the sand, the nassarius becomes almost invisible. Sharp-eyed watchers may see the siphons sticking out of the sand like little snorkels, but, for the most part, the snails disappear. As soon as the snails scent food in the water, however, they erupt from the sand like zombies from a graveyard. Most of the time, all seven of my nassarius break from the sand within a couple of seconds — a dramatic, and sometimes amusing, surprise, especially when I have company that hasn’t seen it happen.

Nassarius come in a range of colors, though most fall somewhere on the spectrum between black and white – with tans and even purples a possibility. Many have spots, and sometimes the snail’s body has a different color than its shell–though that’s more rare.

14A14 Nassarius 3

As reef inhabitants go, nassarius are peaceful and valuable because they eat only things that don’t “belong” on the reef, without bothering corals or other living creatures.

Most people find it odd to consider a snail “valuable” or “fun to watch” — but every reef keeper I know agrees that nassarius snails are both.

Have you ever watched a snail — aquatic or terrestrial?