Introduction 

For many shell collectors it is only the color, shape or shine that matters. For others the rarity is important as it adds status to their collection when a rare specimen is present. In many cases little is known about the place of origin of the shell, i.e. where and how the animal lived remain unanswered questions. For everyone interested in the answers to these questions, I will briefly describe the habitat and ecological position of the most popular groups of shells living on tropical coral reefs. This is the place where marine gastropods are most abundant and show an extra-ordinary variety in shape and color. It is also the place where most of the collecting is done.

Besides my own observations, I used the information given by Y.I. Sorokin (1995) in Vol. 102 of the series Ecological Studies: Coral Reef Ecology (Springer, Berlin); and by John D. Taylor (1971) in his study on Reef Associated Molluscan Assemblages, issued in vol. 28 of the Symposium of the zoological Society in London. For nomenclature I mostly followed Tucker Abbot and Peter Dance's Compendium of Seashells (1986). I hope that these pages may contribute to the knowledge and pleisure of many starting collectors. A few black and white drawings may help to place a shell in the right group where it belongs.

Introduction of molluscan families on the reef 

The bottom fauna of coral reefs is extremely rich and varied. To give an idea, reef inhabitating animals include tens of species of sponges, echinoderms and forams; a hundred or more different species of crustaceans and polychaetes; and several hundreds of species of molluscs. This high species diversity is the result of fine trophic and ecological partitioning and specialisation.

Molluscan species, the ones most collectors are interested in, occupy all the bottom econiches: surfaces of sediments and rocks, crevices in those surfaces, dead coral heads, living corals, and seagrass stems and leaves. Molluscan communities are represented mainly by bivalves and gastropods, plus species of tusk shells (scaphopods) and chitons. For collectors the gastropods are the most attractive group because of their shapes, color, shines and general beauty. Therefore I will concentrate on that group only.

In coarse coral sands and rubble omnivorous micromolluscs, with a shell of less than 7 mm, can be found in large numbers. They belong to the periwinkles (Littorinidae) and risso snails (Rissoinidae). Small and medium seized gastropods found in this habitat include the keyhole limpets (Fisurellidae); periwinkles (Littorinidae); true limpets (Patellidae); top-shells (Trochidae); risso snails (Rissoinidae); and planaxis snails (Planaxidae). Abalones and ormers (Haliotidae) and stomatella tops (Stomatellidae) are common on the rocks of the reef flat and on outer slopes. Turban shells (Turbinidae) are found on reef flats. Ceriths (Cerithiidae ) can be found in the trenches of the rocks at the reef flat edge and on beach rocks. They are detritus feeders, like the true conches (Strombidiidae),  another abundant family in shallow areas of the reef flat and lagoon. Also abundant in this habitat are the worm shells (Vermetidae).

Cowries (Cypraeidae), one of the best known families among shell collectors, inhabite all biotopes of the reef. Unfortunately, they are eagerly collected by tourists and local inhabitants because of their gloss and shine.

Soft bottom biotopes are inhabited by micromolluscs, risso snails (Rissoinidae), stomatella tops (Stomatellidae), dove shells (Columbellidae), ceriths (Cerithiidae), auger shells (Terebridae), true conchs (Strombidiidae), carrier shells (Xenophoridae) and hoof shells (Hypponicidae).

The predatory gastropods, either feeding on other molluscs, other benthic animals or coral, include many well-known families like murex shells (Muricidae), rock shells (Thaisidae), cones (Conidae), and miters (Mitridae). Like members of other well-known groups such as tun shells ( Tonnidae), marginella's ( Marginellidae), neptunes, whelks and goblets (Buccinidae) and vases (Vasidae), they feed mainly on other molluscs and polychaetes.

The corallovorous gastropods are characterized by a firm toothed radula to scrape out the tissues from the surface of coral colonies. They are represented by the sundials (Architectonidae), wentletraps (Epitonidae), coral shells (Magilidae), rock shells (Thaisidae) and egg shells (Ovulidae).

Up to about one quarter of the total number of species of molluscs on reefs are bivalves. The oysters (Ostreae) occupy the rocky littoral biotopes with strong wave action. When wave action is less, sea mussels (Mytilidae), winged oysters (Pteriidae), pen shells (Pinnidae) and hammer oysters (Malleidae) are found. On patch reefs and in dead coral there are file clams (Limidae), tree oysters (Isognomidae), ark clams (Arcidae) and giant clams (Tridactinidae) to be found.

Free living bivalves inhabit the sandy bottom of channels crossing the reef flat and the bottom of the lagoon. Here scallops (Pectinidae), clams (Cardiidae), corbula clams (Corbulidae), Venus clams (Veneridae), sunset clams (Psammobilidae), tellins (Tellinidae) and lucina clams (Lucinidae) are found.

Gastropods in more detail

The grass beds. On the sediment surface and on the grasses we find the hump-back conch (Strombus gibberulus), the mutable conch (Strombus mutabilis) and others. This is also the habitat of the spider conches (Lambis lambis; Lambis truncata), the ring cowry (Cypraea annulus), the money cowry (Cypraea moneta) and the tiger cowry (Cypraea tigris). There are also nassa shells (Nassarius sp.) and several cones, like the lettered cone (Conus litteratus), the leopard cone (Conus leopardus), the beech cone (Conus betulinus), oak cone (Conus quercinus) and virgin cone (Conus virgo). It is also the habitat of small nerites (Smaragdia sp.), small ceriths (Cerithium sp.), small pheasant shells (Phasianella sp.) and small dove shells (Pyrene sp.).

In the sand the bivalves are dominating, but moon shells (Natica sp.) are frequent gastropods in this habitat as well.

Under limestone or dead coral blocks which are scattered over the surface of the grass beds, we find drupes (Morula margaritiola), as well as more cowries and cones.

Unvegetated sands. In unvegetated sands on reef flats we find several burrowing clams and cockles and a variety of gastropods. These gastropods are also burrowers and include many species of auger shells (Terebra sp.), the crowned cone (Conus coronatus), the tessalate cone (Conus tessulatus) and other predators like ribbed miters (Vexillum sp.), moon shells (Natica sp. and Polinices sp.), harp shells (Harpa sp.), horse conches (Pleuroploca sp.), and small tritons (Cymatium sp.). Scavengers are represented by olives (Olivia sp.) and nassa snails (Nassarius sp.), and herbivores and general browsers by the rough and articulate vertagus (Rhinoclavis aspera and Rhinoclavis articulata), the silver conch (Strombus lentiginosus), the terebra pyram (Pyramidella terebellum) and the needle pyram (Pyramidella maculosa). In deeper water besides the miters (Mitridae) and auger shells (Terebridae), turrids (Xenoturis sp.) occur.

The littoral zoneThe fringe of the littoral zone is exploited by members of a single family only, the periwinkles (Littorinidae). The eulittoral is much more varied, with algal grazers predominantly on the upper part. Here we find a variety if limpets (Ptellidae), including the genera Cellana, Acmaea, and Patella. This is also the habitat for nerites (Nerita sp.) and monodonts (Monodonta sp.). Cemented to the rocks are oysters (Crassotrea sp.) and mussels (Brachiodontes sp. and Septifer sp.).

In this habitat a lot of predatory gastropods are present, like murex shells, neptunes and whelks, miters and cones. The biggest group are the murex shells (Muricidae), with Rudolph's purpura (Purpura rudolphi), the aculeate rock shell (Thais aculeata), the belligerent rock shell (Thais armigera), the purple Pacific or mulberry drupe (Drupa morum), the prickly Pacific drupe (Drupa ricinus) and other drupes (Morula granulata and Morula anaxeres).

The cones are not very successful in this zone. Only the Hebrew cone (Conus ebraeus) and the marriage cone (Conus sponsalis) do occur here.

The major part of the reef platform falls within the sublittoral zone with a variety of hard substrate habitats like the flat pavement, dead coral, boulders, calcareous algal growths and surge channels. This is the place for a diversity of molluscs and a distinction must be made into species which occur on open surfaces and those which are restricted to shelter beneath boulders and cobbles, and in crevices. The bivalves are all suspension feeders and include mussels (Modiolus sp.), oysters (Pinctada sp. and Ostrea sp.), ark clams (Arca sp. and Barbatia sp.), cardita's (Cardita sp.), jewel boxes (Chama sp.) and the giant clam (Tridacna maxima), which can reach a weight of 300 kg and a length of one meter. The tissue of its mantle contains a mass of algal cells and the product of their photosynthesis is used by the host. Most of the gastropods are grazers upon encrusting animals. Algal grazers are not abundant here, they are largely restricted to the seaward edge of the platform where circulation is at its optimum.

On open surfaces we find grazers like the rough turban (Turbo setosus) and the silver-mouth turban (Turbo argyrostoma), the maculated top (Trochus maculatus) as well as other tops (Trochus flammulatus and Tectus mauritianus), several small ceriths (Cerithium sp.) and risso snails (Rissoina sp.).

A variety of predatory cones can be found on reef platforms, e.g. the livid cone (Conus lividus), the yellow Pacific cone (Conus flavidus), the Hebrew cone (Conus ebraeus), the vermiculate cone (Conus chaldeus), the crowned cone (Conus coronatus), the marriage cone (Conus sponsalis), the cat cone (Conus catus) and the lithographic cone (Conus lithoglyphus). In sand pockets the textile cone (Conus textile) has its habitat.

Another abundant group here are the drupes (Muricidae). On open surfaces and boulders the purple Pacific drupe (Drupa morum) and the prickly Pacific drupe (Drupa ricinus), the tuberose rock shell (Thais tuberosa) and the mulberry whelk (Morula granulata) can be found. On de shaded underside of boulders the shouldered castor bean (Morula margariticola), the grape drupe (Morula uva) and the small drupe Maculotriton digitalis can be found.

Other common predators on the reef flat include the granulate frog shell (Bursa granularis), the Nicobar hairy triton (Cymatium microbaricum), the intermediate hairy triton (Cymatium pileare), the common Pacific vase (Vasum turbinellus), the lettered miter (Mitra litterata), the kettle miter (Mitra cucumerina), dove shells (Pyrene sp.), engina's (Engina sp.), the precious stone shell (Leucozonia smaragdula), and a latirus (Latirus craticularis). The last two species belonging to the tulips and spindles family (Fasciolariidae).

Very popular among collectors are the cowries from the reef flat zone. On the boulder zone the histrio cowry (Cypraea histrio), the Pacific deer cowry (Cypraea vitellus), the lynx cowry (Cypraea lynx), the fimbriate cowry (Cypraea fimbriata), and the carnelean cowry (Cypraea carneola) are present. In crevices the serpent's head cowry (Cypraea caputserpentis) is found, whilst on the midrif platform the honey cowry (Cypraea helvola), the isabelle cowry (Cypraea isabella) and the caurica cowry (Cypraea caurica) have their habitat. Other cowries, like the grape cowry (Cypraea staphylea) and the limacina cowry (Cypraea limacina) are usually found in the lagoon.

This is only a rough outline and one should not be surprised to find many of the gastropods mentioned above in other habitats as well.