Shells of the Turks and Caicos Islands In the last article I looked at some of the large and showy gastropods, but in this one I will concentrate on the smaller species. However, because I am grouping the shells according to their families, and every family has its odd man out, one or two larger ones will crop up as we go along.
Costate Horn Shell Cerith and Horn shells Many shells in a variety of families are pointed, or spired. The commonest are the Ceriths (family Cerithiidae), which are probably the most abundant shells on the beach, but there are many other types. Very similar in appearance are the Horn Shells (family Potamidae). On Providenciales you can find tiny Costate Horn Shells (Cerithidea costata) whose brown spire is a coiled tube about an half-inch high, while another Horn Shell, the False Cerith (Batillaria minima), abounds everywhere. It and the tiny Dwarf Cerith (Cerithium lutosum) are what flamingos are straining the water for.
Wentletrap shells Wentletraps (family Epitoniidae) are small shells, consisting of a spiral tube linked by vertical blades. Brilliant white, and about an inch long, they get their name from an old German word for a spiral staircase. They are not common in the Turks And Caicos Islands, but two species do turn up occasionally: the Bladed Wentletrap (Epitonium albidum), and the smaller Angulate Wentletrap (Epitonium angulatum). Pryam and Auger shells On Caicos beaches you can commonly find Giant Atlantic Pyrams (Pyramidella dolabrata, family Pyramidellidae). They are glossy white, with a brilliant yellow line revolving around the spire, but their small size (an inch at most) belies their name. The Shiny Atlantic Auger (Terebra hastata) is the only representative of their family (Terebridae) in the Turks And Caicos Islands. They are common on Caicos beaches but rather rare in the Turks Islands. Mitre and Turrid shells The Mitres (family Mitridae) are represented by the Barbados Mitre (Mitra barbadensis), whose chocolate or orange spire, mottled with white, rarely exceeds one and a quarter inches. The smaller White-lined Mitre (Pusia albocincta) and Beaded Mitre (Mitra nodulosa) also turn up occasionally. And then there are the Turrids (family Turridae): all small and hard to identify to species, these shells can be assigned to the Genus by a notch (called the Turrid Notch) in the outer lip at the top of the aperture.
Moon and Tun shells shell-28Moon and Natica Shells Moon Shells (family Naticidae) look like typical snails, and the immaculate white Milk Moon-Shell (Polinices lacteus) is one of the commonest shells in the Turks And Caicos Islands. The larger Colourful Atlantic Natica (Natica carena) is the same shape, but is gaudily patterned in shades of brown and white. In a family of its own (the Tonnidae) the Atlantic Partridge Tun (Tonna maculosa) is a snail with a delicate, inflated shell that feels like a fine wine glass. They usually have a brown pattern, said to resemble a partridge’s wing, but deep water specimens can be a uniform chocolate in colour. This shell is common on beaches in sizes of up to one inch, but on rare occasions big specimens of up to six inches can turn up.
Nerite shells Another group of snail-like shells is the Nerites (family Neritidae), which live on rocks at, and above, the high-water mark, where they graze on algae. The commonest is the Four-toothed Nerite (Nerita versicolor), but the one which is a favourite with everyone is the Bleeding Tooth Nerite (Nerita peloronta), so called because the inner edge of its aperture is toothed and stained blood red. The Tessellate Nerite (Nerita tessellata), at about three-quarters of an inch, is the smallest of the trio of the larger Nerites. shell-34There is also a trio of small Nerites, each of which is astonishingly beautiful. Virgin Nerites (Neritina virginea) live on filamentous seaweed in muddy pools. They are glossy and brightly coloured in a multitude of exquisite patterns, no two of which is ever the same. Their cousins, the Zebra Nerites (Puperita pupa), live on rocky shorelines in splash pools above the high-water mark, which are kept full by the spray from waves. Their exterior is patterned with black and white stripes, but the aperture is a startlingly rich yellow. The bright green Emerald Nerite (Smaragdia viridis) makes up the trio. It lives on Turtle Grass, from which it may get its unusual colour, and its tiny shell (less than a quarter of an inch) is common on beaches which fringe grassy beds.
Periwinkle shells The Nerites which live on the tide line share their habitat with the Periwinkles, which take their family name, Littorinidae, from the Latin word for seashore. They range in size from the tiny Dwarf Brown Periwinkle (Littorina mespillum) up to the Angulate Periwinkle (Littorina angulifera), a relative giant at one inch. In between is the small Zebra Periwinkle (Littorina ziczac), whose half-inch grey shell is covered with zebra-like stripes in black and brown. The Prickly Periwinkle (Nodilittorina tuberculata) and the enigmatically named False Prickly-winkle (Echininus nodulosus) check in at about three-quarters of an inch. The slightly larger Beaded Periwinkle (Tectarius muricatus) strays so far above the tide line that it is well on its way to becoming a creature of the land, following in an evolutionary trail taken by the ancestors of land snails and slugs many millions of years ago.
Top shells The Top Shells (Trochidae) include the large West Indian Top Shell (Cittarium pica), which has long been a delicacy in the region under the local name of whelk. In life, the colouration of its boldly striped black and white shells is often obscured by the same algae that it browses on as it crawls over the rocks on which it lives. Under those rocks, and belonging to the same family, you can find the flattened spirals of the brightly coloured Smooth Tegula (Tegula fasciata) and its duller cousin, the West Indian Tegula (Tegula lividomaculatus).
Star and Turban shells shell-39Star and Turban Shells do not look much alike, but they are members of the same family, the Turbinidae. Representing the Turbans in the Turks And Caicos Islands, and shaped just like their name suggests, are the Chestnut or Knobby Turban (Turbo castaneus) and the larger Channeled Turban (Turbo caniculatus). Both are well named, for the former is chestnut coloured, with white markings, and is covered with little knobs arranged in spirals around the shell. The latter is a mottled brown and white, with a marked channel or groove following the suture where the coils of the spire join. The name of the Long-spined Star-shell (Astraea phoebia) is also a good description of the shell itself, which is flattened with projecting spines, which give it a star-like appearance (although some think they look more like circular saw blades). The carved Star Shell (Astraea celata) has a more conventional shape, but its robust shell is covered with spiny projections. It is common on the reef, but in life its wonderful mottled green colour is obscured by chalky encrustations. The American Star-shell (Astraea americana) looks more like a round pyramid, as its spire is high and straight-sided. Last and also least is the tiny Star Arene (Arene cruentata), whose small white shell, candy-striped in pink and brown, can sometimes be found under rocks.
Whelk shells The whelk family (Buccinidae), well-represented in northern waters, has only four representatives in the TCI, none of them large. The biggest is the Miniature Triton’s Trumpet (Pisania pusio), a brown shell of about two inches, decorated with a spiral of chevron markings. The Tinted Cantharus (Pisania tincta) is half the size, and its well-ribbed shell is mottled brown and white. The half-inch White-spotted Engina (Engina turbinella) is circled by white knobs, and has a pink aperture, with pronounced teeth on the inside of the lip. Equally small, but less stubby, the Intricate Bailey Shell (Bailya intricata) has a high spire decorated with a filigree of raised ribs and intersecting lines.
Dove Shells Dove Shells (family Columbellidae) are well represented in the TCI. The small Common Dove Shell (Columbella mercatoria) is abundant on beaches fringing grassy lagoons, where its sturdy shell survives a long time. It is the largest of its family in the TCI, although several smaller species also occur, including the aptly named Glossy Dove Shell (Nitidella nitida) whose half-inch shell is brown with a pattern of white blotches. The spots on the White-spotted Dove Shell (Mitrella ocellata) are more discrete, and their brown background darker and richer, which makes for a tiny jewel of a shell. Less well-known, but quite common, is Pyrene ovulata, which looks a bit like a small brown cone shell. Similar in size and glossiness, but of a different family, is the Oat Marginella (Hyalina avenacea). As its name suggests, it resembles an oat grain, and is a pale orange, fading to white on the beach.
Other tiny shells There are many other tiny jewels to be found on the beaches of the TCI. Hidden amidst the grains of sand you can pick out minute Checkered Pheasant Shells (Tricolia affinis, family Phasianellidae), whose plump little spires of glossy translucence are covered in zigzag stripes of pink and yellow. Two members of the Planaxidae can be found in sheltered lagoons. The Black Planaxis (Supplanaxis nucleus), is a shiny, jet black snail of half an inch. Half its size is the tiny Dwarf Atlantic Planaxis (Angiola lineatus), a glossy white shell with revolving brown lines. The half-inch Coffee Melampus (Melampus coffeus, family Ellobiidae) is a polished chocolate brown, with two revolving coffee-coloured lines. The Variable Nassa (Nassarius albus, family Nassariidae) is a plump little white shell of half an inch, patterned with intersecting raised ribs and revolving lines. It could be mistaken for a Wentletrap, but it is rounder and chunkier. The Atlantic modulus (Modulus modulus, family Modulidae) is a flattened white spiral of less than half an inch in diameter, decorated with radiating brown lines.
Limpet shells Finally, there are the Limpets (family Acmaeidae). Their dead shells resemble a valve from a bivalve, but in fact they are primitive gastropods, although their pyramidal shells lack the characteristic spiral of the more advanced members of that class. Although the exterior of the shells is often covered in encrustations, the interior can be beautifully glossy and attractively marked by scars to which the muscles of the living animal were attached. In particular the Eight-ribbed Emarginula (Hemitoma octoradiata) has a lovely gray interior with a rich, satin sheen, while that of the Southern Limpet (Lottia antillarum) is boldly marked with a circular red scar. In life, Limpets live tightly adhered to rocks and other hard substrates, on which they browse on algae. They share this environment with the segmented Chitons, which belong to a completely different class of molluscs, the Polyplacophora. There are also various limpet look-alikes, such as False Limpets, Hoof Shells and Cup and Saucer Shells. shell-48Keyhole limpets (family Fissurellidae) are distinguished from true limpets by the hole at the apex of the shell. Some are attractively patterned, such as Lister’s Keyhole Limpet (Diodora listeri), with its eight rays, but this is usually concealed by heavy encrustations. As with the true Limpets, the most obviously beautiful part of Keyhole Limpets is their shiny interior. The easiest to identify, and amongst the commonest, is the Barbados Keyhole Limpet (Fissurella barbadensis). Its interior is a lovely green colour, but this fades quickly on beaches. To be continued in Fall 2004 Times of the Islands. In the third and final article in this series, the author will deal with Bivalves, whose flat shells will be familiar to all beachgoers. Richard Ground has been Chief Justice of the Turks & Caicos Islands since 1998, recently leaving to take up an appointment as Chief Justice of Bermuda. When not at work, his main interest is wildlife photography, with an emphasis on birds. Shells are a new departure; describing himself as an insatiable collector and cataloguer, he says it was not long before he was sorting his finds and searching for rarer and more beautiful specimens.
Story and Photos by Richard Ground This is the second in a series of three articles about the shells of the TCI.