Seashells of Sri Lanka
Sri Lanka, a tropical paradise set in the central Indian Ocean, is surrounded by the sea. Shallow at the north-western end where it abuts India but with the sea-bed shelving down to deep water around the rest of the perimeter, it has numerous habitats that are home to many species of animals and plants. The habitats range from shallow or deep sandy bottoms to shallow or deep rocky bottoms that are the present day reefs lying a few metres below the surface or sunken reefs many metres deep that represent ancient shore-lines. In addition, there are estuaries and lagoons with muddy bottoms and water ranging from saline to brackish to near-fresh. All these habitats are home to different species of molluscs whose outer shell is the familiar seashell, all evolved to live and thrive in a particular environment and lifestyle.
The molluscs comprise a large group of related animals with diverse body forms and lifestyles ranging from the bottom dwelling octopus, swimming squid and cuttlefish to snails, clams, sea slugs and others. This article deals with the snails and clams that have a solid external shell - the seashells that we see washed up on beaches that many of us have collected as children. Snails - similar to garden snails and tree snails externally - have shells in one piece and they crawl about on a large foot (and are termed gastropods); clams on the other hand have their shells in two pieces (hence called bivalves) joined together by a hinge and either live a sedentary life attached to something solid, or are free living and mobile on sandy or muddy bottoms, often burrowing into the substrate.
The shells of Sri Lanka have not been studied much - particularly in recent years. We are uncertain as to the total count of species around our shores. The provisional checklist of shells published in 2012 lists about 800 species, 1 culled from a number of sources. There is an ongoing study to collect and list species that have been overlooked by previous workers, with many finds turning up that have not been recorded before from Sri Lanka. The pictures on these pages are from this collection. An attempt has been made to illustrate a range of shells of different shapes, from different habitats, including those that are of commercial importance and those at risk of over-exploitation. This latter fear has been addressed by some species being given specific legal protection by declaring them protected under the Fauna and Flora Protection Ordinance. But the same ordinance gives blanket protection to all wildlife and their parts, specifically preventing their export. This results in a somewhat confusing situation where shells are offered for sale - to tourists as well as residents - but their removal from the country may be prevented by the customs authorities
Fernando, Malik, 2012. Provisional Checklist of Marine Aquatic Shelled Molluscs of Sri Lanka. In: The National Red List 2012 of Sri Lanka; Conservation Status of the Fauna and Flora, Weerakoon, D. K. & S. Wijesundara Eds., Ministry of Environment, Colombo, Sri Lanka. 384-395 pp
Sri Lanka has been renowned in the past for its pearls, extracted from the pearl oyster (Fig. 1). The term 'oyster' as applied to this bivalve is a misnomer: true oysters are attached to a hard substrate by one of its two shell pieces (valves), whereas other clams (a generic term for a bivalve) such as mussels (Fig. 2) are attached to a hard substrate by a leash of fibrous threads called a byssus. Other clams that attach their shells directly to the substrate are the jewel boxes - the Lazarus jewel box is a particularly striking example (Fig. 3). Pearl oysters belong to the family of wing oysters, some species possessing exaggerated shapes, like that in figure 4. These shells are found attached by a byssus to types of soft corals called sea fans and sea whips.
Perhaps the best known of the shells that cement themselves to rocks are the true oysters (Fig. 5). These range in size from about 50mm to nearly 300mm. There are many species, attached to rocks, other shells, and one species even to sea whips - from beach level down to depths of many metres; some species are also found in brackish water lagoons. A few species are farmed, or wild collected, for local consumption at restaurants. Very popular at specialised seafood restaurants are clams of the Venus clam family. This is a very large family with shells of various shapes, some of them highly coloured. Illustrated are the two clams seen most often in high-end markets and served up in seafood risotto (Figs. 6 & 7) . Scallops are also molluscs prized as food in many countries, but the Sri Lankan species are generally small and not harvested for eating. Many are very colourful (Fig. 8).
There are many more species of marine gastropod snails than there are bivalves. They range in size from micro-molluscs only a few millimetres long to species which grow to 300mm or more. Most snails are thick-shelled, many being brightly coloured and ornamented with ridges, grooves, knobs and spines. Only a few can be shown here. One that is seen often in everyday life is the chank (Fig. 9), incorrectly referred to as conch. The shell is made into a trumpet by sawing off the pointed end and is used in traditional welcome ceremonies to produce one-note sustained blasts. A rare form of this shell is called valampuri colloquially. The shell winds in an anti-clockwise direction when viewed from the pointed apex, instead of the usual clockwise direction. They are said to bring great fortune to the owner and so are much sought after. But being very rare they are also very expensive. Care should be exercised if purchasing one of these so-called valampuris that are sold by traders as they are likely to be an Atlantic Ocean species (Busycon) quite unrelated to chanks that are always anti-clockwise.
The best-known shells are the cowries - hump-backed, glossy, variously patterned and coloured. These herbivores live on rocky bottoms. Two of the more uncommon species are shown (Figs. 10 & 11) , both protected. The cone shells - so-called on account of their shape - are also beautifully patterned and coloured (Figs. 12 to 15) . Some species are notorious because the venom used to capture their prey is potent enough to kill an adult human - if an unwary person picks up a live shell and is stung. All the shells mentioned so far live immersed in water. However, a number of species live at the tide line and may be exposed out of water for longer or shorter periods throughout the day. They are small, yet colourful, but often covered in a green coloured film of algae. There are a number of species called limpets (Fig. 16) adapted for life on exposed rocks where they are battered by breaking waves; they are streamlined smooth, low-profiled cones in shape. Higher up on the same wave-washed rocks are the periwinkles (Fig. 17) - small shells with a typical snail's appearance. They are adapted to drying out at times and are able to seal themselves within their shells by means of a hard flap called an operculum, at the same time cementing the edge of the shell to the rock so they do not fall off.
A question that is frequently asked relates to the number of endemic shell species in Sri Lanka - i. e. found only in Sri Lanka. We have no species proved to be endemic. In most marine species the eggs hatch into larvae that are liberated into the water to drift with the currents till they develop into miniature adults, whereupon they settle on to a suitable bottom. This means that most marine species - not only the shells - are distributed over a wide area, not confined within country borders. Some species however, produce creeping larvae that settle on the bottom straight away and are not then distributed far and wide, being more local in occurrence. This is the case with the volutes of which two species are illustrated (Figs. 18 & 19). One from the north of the island and one from the south, both from deep water, collected in fishing nets, and both rare. These are the nearest we have to endemic shells.
Finally, two spectacular shell species to finish off with. Spider conchs are sand dwellers with long spines curving out from the edge of the opening. A number of species are found in Sri Lanka's waters, one growing to be over 300mm in length. Rather smaller, but strikingly coloured inside, is the species illustrated (Fig. 20) . Perhaps the most spectacular of the country's shells is the Venus comb murex (Fig. 21) . Sombrely coloured, it makes up for this with an extravagant display of spines. Both live on sandy bottoms.
Many of Sri Lanka's shell species are found all round the coast, but may be restricted to particular areas by their habitat preferences such as water clarity, rocky reefs, coral reefs, sandy, muddy-sand or mud bottoms etc. Also of importance are water conditions such as still waters, fast-flowing currents and exposure to wave action. Many species are being depleted either by over collection or by being ensnared in (illegal) bottom-set fishing nets. Please do not encourage unsustainable commercial collecting.
Figure 1
Black-lipped pearl oyster Pinctada margaritifera .One of the two species of pearl oysters in Sri Lanka.They do not exceed 100mm in this country but grow to nearby three time that size in the Torres Steaits
Figure 2
Mussels: Perna viridis. Grows to about 100mm in lenght. The commoner brown mussle in smaller.Both are edible and offerd for sale
Figure 3
Jewel box: Chama lazarus. One of a number of species in the island and the most spectacular
Figure 4
Wing oyster: Pteria brevialata. The hinge is greatly elongated,hence the shape.Four other speicies of various size,usually attached to branching soft corals,the smallest to a stinging hydriid.Same family as the pearl oysters.
Figure 5
rock of Bombay oyster: Saccostrea cucullata. Growing up to about 80mm these gregarious oysters grow crowded on rocks along the beach at the leveol of the hightst tides.Drying out at low tides,
Figure 6
Venus clam,hiant clan: Marcia hiantina. A beautiful golden yellow and very tasty 45mm
Figure 7
Venus clam.meretrix venus: Meretix meretrix.The shell is shown from the top, with left and right valves to either side.the black colour behind is characteristic.55mm.
Figure 8
Scallops: Chlamys spectabilis,Ch.irregularis. Unknown species,Ch.sentorious .Four outv of a number of species of scallops in Sri Lanka wares.Mostly small and not commercially fished
Figure 9
Secred Chank: Turbinella pyrum. Two varieties of chanks are found around the cost. There is a large organised commercial fishery for these shells that are expoted to the sub-continent for the manufacture of jewellery and ornaments.In life they are coverd by a thick brown 'skin'. In the rare valampuri the shell opening would be on the left of the shell.Up to 170mm
Figure 10
Eyed cowries: Cypraea argus. This has a cylinderical shape with the long,narrow opening on the under-side as in all cowries. 80mm
Figure 11
Map cowries: Cypraea mappa. This cowrie has the bulbous shape common to most species.It gets its name from the pattern on the upper surface,fancifully likened to a geographic map 80mm.
Figure 12
Abbas cone: Conus abbas. This and the following striate cone posses potent veno, able to har humans.The abbas cone belong to the group of textile cones,on account of the closly woven patterns.50mm.
Figure 13
Striate cone: Conus striatus.90mm
Figure 14
Soldier cone: Conus miles. A pretty non-venmous cone.50mm
Figure 15
Cloud cone: Conus nibbosus An uncommon cone with fine ridges around the outside making it rough to touch.All cones have long,narrow openings at the side 40mm.
Figure 16
Periwinkles: Littoraia undulata,echinolittorina millegrana,Nodillttorina torchoidea and N.quadricinata.these four,out of the six,periwinkle species often cluster together,mostly aboove the tide line where they dry ou at times.They are smal raging from about 10 to 20mm in size
Figure 17
Limpets: Cellana rota,Patelloida striata and Clypidina notata.these three belong in three diffenrent families but often live clustered together in colonies.Some of the images are useful in identifying them.they are small 10 to 25 mm
Figure 18
Vexilate volute: Voluta (Harpulina) arausiaca.A volute found off nothern Sri Lanka and southern india growing to about 75mm. rare.
Figure 19
Clover's Lyria: Voluta(Lyria) cloveriana.A volute found off southern Sri Lanka growing to about 85mm.Rare,but seems to be locally frequent.
Figure 20
Orange mouth spider conch: Lambis crocata.two other species are on the protected list.It is rarely that one finds these shells with the spine unbroken,and so strongly coulourd.125mm overall.Bigger shells with pale interior and damaged spine
Figure 21
Venus comb murex: Murex pecten.One of a group of sand bottom-dwelling canivoures that drill holes into bivalves and suck out the flesh, this is the most spectacular.Growing to about 130mm in lenght it has three rows of sharp ,slender spines.Other species have fewer and shorter spines.