‘She sells seashells by the seashore. The shells she sells are surely seashells. So if she sells shells on the seashore, I’m sure she sells seashore shells,’ goes the popular tongue-twister.

Seashells are fascinating, curious objects: they come in different shapes, colours and sizes, and one may find hundreds, if not thousands, washed ashore. To add to their allure, as kids we were told that if you put a large seashell to your ear, you can hear the sea. Actually, the shell simply amplifies the ambient noise around you, but this doesn’t take away the charm.

To date, almost 100,000 species of molluscs have been described worldwide

Everyone must have looked for a big shell and listened to it, at least once in their life. But have you ever wondered who the seashells belong to or where they come from?

Marine biologist Alan Deidun explains that the shells one encounters on beaches belong to four different groups of marine molluscs:

• Gastropods, which include the ‘standard’ coiled up shells of snails;

• Bivalves, such as clams and oysters, whose shell consists of two halves or valves;

• Scaphopods, the tooth or tusk shells, which, as their name implies, resemble miniature elephants or walrus tasks; and

• Limpets, whose flattened bodies cling close to the surface of rocks to prevent being dislodged by the pounding waves.

To date, almost 100,000 species of molluscs have been described worldwide. And different species live in different parts of the world, therefore one would find different seashells washed ashore in different parts of the world.

“Molluscs are one of the most diverse animal groups to be found and biodiversity is not distributed homogenously around the world,” says Deidun.

“Generally, the highest level of biodiversity is found in the tropics, although even beaches lapped by highly-productive waters, such as those close to an estuary, would be expected to support large diversities of filter-feeding molluscs such as bivalves.”

As regards Malta, Deidun says that the more gently sloping a nearshore area is, “the greater the probability that shells and other remnants of marine life will be washed up ashore”.

Exposure to wave action is yet another aspect taken into consideration.

“It’s difficult for sheltered areas to accumulate shells, with the exception of harbour areas, whose nutrient-laden waters are conducive to large bivalve populations.”

Most molluscs also thrive on seabeds supporting vegetation.

“From personal experience, low-lying areas along the western flank of Malta (e.g. Fomm ir-Riħ) and the northern shores of Gozo (e.g. Xwejni Bay) are the best spots to visit if you have a penchant for shells,” he claims.

Not all seashells, however, have the potential to be beached along the coastline.

“A number of them are too heavy or else inhabit waters which are too deep to be carried up on land. But the scale of the potential variety in beached seashells is still stunning.”

He adds that very rarely, one may also encounter chiton shells or “even more esoteric finds”, such as the wafer-thin egg case of the paper Argonaut, a species of pelagic octopus, or encounter hard, non-mollusc body parts on a beach, such as the tests (skeleton) of sea urchins or detached barnacles (a group of crustaceans).

Another question which props up spontaneously is why, most often, we find the shells empty.

“The shells of marine molluscs are more resistant than those of terrestrial ones to degradation. When still alive, the mollusc would not be carried about haphazardly by the elements, such as bottom currents and waves, by attaching themselves to rocks, for instance. Such molluscs can’t tolerate being out of the water for long periods of time,” he points out.

“Once they hit the dust, however, it’s only the soft body parts which disintegrate, with the hard empty calcareous shell far outliving its resident.”

These empty shells are much sought after by hermit crabs, at least before they are beached up, since these soft-bodied crustaceans inhabit the empty shells so as to avoid becoming morsels of food for others.

Actually, seashells are also sought after by humans, either because they collect them or else to use them in crafts.

Deidun maintains that beachcombing is a pretty safe activity for the environment, however, one should stick to a proper code of conduct (see box below). Also, one should be aware that some seashell species are protected by law, “even when the soft mollusc resident is no longer there”.

These species include a number of cowries (baħbuħ in Maltese), the giant tun, the noble pen shell (the largest bivalve in the Mediterranean, to which it is endemic) and the giant triton/triton’s trumpet.

The pinna nobilis or noble pen.

Responsible beachcombing

• Avoid picking animals which are still visibly alive. Some creatures, such as hermit crabs, can be pretty elusive, giving the impression that no one’s home when you pick up a seemingly empty shell, since they manage to retract their bodies completely inside the same shell.

• Some species are protected by law in Malta, including a number of cowries, the giant tun, the noble pen and giant triton or triton’s trumpet.

• Avoid disturbing rock pools too much, by, for example, dragging hand-nets along the bottom of such pools, stirring up the bottom sediment and making the water turbid.

• Avoid disposing of any litter you might be carrying with you, including cigarette butts, since the rocky and sandy coastline is peppered with such human artefacts.