The gastropods (snails & slugs) are a group of molluscs that occupy marine, freshwater, and terrestrial environments. Most gastropods have a calcareous external shell (the snails). Some lack a shell completely, or have reduced internal shells (the slugs & sea slugs & pteropods). Most members of the Gastropoda are marine (see modern examples below). Most marine snails are herbivores (algae grazers) or predators/carnivores.
The conid gastropods (cone shells) are fascinating marine snails for a couple reasons - they have attractively-shaped, colorful shells and they are killers. The conids are predatory, as are many other marine snails, but they take down their prey in an unusual fashion. The radula of most snails is a mineralized or heavily sclerotized mass of small teeth that scrapes across a substrate during feeding. Conid snails have a toxoglossate radula - one that has been evolutionarily modified into tiny, unattached, toxin-bearing, harpoon-like darts (see photo) that can be fired at prey. Each dart is an individual tooth. The nickname "killer snails" is well deserved (even people have been killed). Some species have incredibly powerful toxins, while in other species the toxin has little effect on humans.
Conus gloriamaris (7.8 cm tall) - abapertural (left) and apertural (right) views. The apertural edge has not been filed (unlike many snail shells in the retail shell market) & the protoconch is present.
The conid shell shown above & below is one of the most famous rare seashells in history - Conus gloriamaris, the glory-of-the-seas cone. Conus gloriamaris (a.k.a. Conus (Regiconus) gloriamaris; a.k.a. Cylindrus gloriamaris; a.k.a. Conus (Cylindrus) gloriamaris; a.k.a. Cylindrus (Regiconus) gloriamaris) is a modern, tropical marine gastropod. The hard shell, or conch, has a distinctively elongated, gently tapering shape and a more sharply tapered top. This species’ shell surface coloration consists of a medium to dark brown colored “tent” pattern on a pale creamy yellow background (many conid gastropod shells have broadly similar tent patterns). Individual tents vary in size.
Conus gloriamaris was first named & described by Johann Chemnitz in 1777. Shell collectors treasured specimens of this species, which remained very rare from the time of its original description up to the late 1960s. Conus gloriamaris is not an abundant species, but shells are now available in the retail market.
Classification: Animalia, Mollusca, Gatropoda, Neogastropoda, Conoidea, Conidae
Natural distribution: intertidal to <100 meters depth, western Pacific Basin.
Conus gloriamaris - apical portion of conch (left) and apical view of conch (right, ~2.5 cm across) showing dextral coiling. Dextrality is an almost universal trait in conchiferous gastropods. Only rarely can counter-clockwise coiled shells be found (left-handed coiling/sinistral coiling).
Conus gloriarmaris - conch surface showing tent pattern (field of view ~2.7 cm across).
Here’s a graceful fig shell (a.k.a. elongated fig shell), Ficus gracilis (see photo of snail inside this shell). This is a modern, predatory, tropical marine gastropod from the western Pacific Basin that inhabits unconsolidated sand substrates and preys on irregular echinoids. The shell itself is relatively thin & lightweight.
Classification: Animalia, Mollusca, Gastropoda, Neogastropoda, Ficoidea, Ficidae
Ficus gracilis shell - abapertural (left) and apertural (right) views (10.3 cm tall). The apertural lip has been filed (this is commonly done to retail specimens).
The colorful queen vexillum shell (Vexillum regina) is spectacularly colored with white, orange, and dark brown stripes (the species does vary in coloration, however). It is a modern, tropical marine gastropod from the western Pacific Basin. Vexillum is a predatory snail that secretes toxins to immobilize & kill prey.
Classification: Animalia, Mollusca, Gatropoda, Neogastropoda, Volutoidea, Costellariidae
Vexillum regina shell (6.2 cm tall) - abapertural (left) and apertural (right) views.
Here’s one of the more bizarre gastropod shells around. This is Vermicularia, also called a worm snail. It’s one of the few snails that does not have a tightly coiled shell. Several snails from different families have shells somewhat like this (e.g., the vermetids & the turritellids). They all resemble the twisted mineralized shells made by some annelid worms, hence the common name “worm snails” or “worm shells”.
Despite the superficially very different-looking shells, malacologists have demonstrated that Vermicularia is very closely related to the high-spired snail Turritella. Juvenile Vermicularia are free living, infaunal filter feeders that position themselves apex-down and aperture-up within the sediment. During this stage in ontogeny, the Vermicularia shell is tightly coiled, as is any ordinary gastropod shell. Later in life, the snail becomes an epifaunal, encrusting filter feeder (assuming hard or firm substrates are available), and its shell starts uncoiling. The advantage of an uncoiled shell in Vermicularia is generally inferred to be rapid upright growth (that’s desirable for a sessile, benthic filter feeder).
If hard or firm substrates aren’t available, Vermicularia generally doesn’t grows an unwound shell during growth, and they end up looking like typical Turritella shells. The degree of uncoiling also depends on the nature of the hard substrate (e.g., a ramose scleractinian coral vs. a hemispherical scleractinian coral vs. a bivalve shell). So, shell uncoiling is an ecophenotypic character.
Classification: Animalia, Mollusca, Gastropoda, Mesogastropoda, Cerithioidea, Turritellidae
Vermicularia (worm snail) (9 cm tall)
Most info. synthesized from Morton (1953) and Gould (1968, 1969):
Morton (1953) - Vermicularia and the turritellids. Proceedings of the Malacological Society of London 30: 80-86.
Gould (1968) - Phenotypic reversion to ancestral form and habit in a marine snail. Nature 220: 804.
Gould (1969) - Ecology and functional significance of uncoiling in Vermicularia spirata: an essay on gastropod form. Bulletin of Marine Science 19: 432-445.
The xenophorid snails (a.k.a. carrier snails), especially members of the genus Xenophora, are remarkable in their tendency to pick up other shells, skeletal fragments, rock fragments, or corals (sometimes still alive) from their surrounding environment and cement these objects to their own shells. The result looks like a pile of shells on the seafloor. Often, sponges and serpulid worm tubes are found encrusting the xenophorid shell - they contribute to the illusion that a xenophorid is simply a patch of seafloor. Xenophora carrier shell snails do this as a camouflage defense against predators. Decorator crabs are arthropods that do this as well.
Xenophorids are principally detritivores on unconsolidated, fine-grained to coarse-grained to rubble-bottom substrates.
Classification: Animalia, Mollusca, Gastropoda, Mesogastropoda, Xenophoroidea, Xenophoridae
Xenophora carrier shell (above & below; 12.7 cm across; above: apical view; below: umbilical view) with numerous attached shells. Most of the objects that have been picked up by this individual are snail shells, but there are also a few clam shells, and a long worm tube.
Some info. from Harasewych & Alcosser (1991) and Hill (1996).
Many muricid snails have highly spinose shells. The high degree of spinosity in such snails is usually considered an anti-predation feature. Spinose muricids typically have three axially-oriented rows of spines per whorl, so that each spine row is ~120º from the next. Conchologists have pointed out that such spine row distributions provide orientation stability to the snail and prevent sinking on unconsolidated, fine-grained, high-water-content sediment substrates. Another suggestion holds that well-developed spine arrays could act as traps for potential prey. Muricids are predatory gastropods, but they principally prey on encrusting, conchiferous organisms (e.g., bivalves, barnacles) by boring through the shells. It's more likely that the spine arrays protect the snail from predatory arthropods or fish while engaged in boring & feeding on prey.
Classification: Animalia, Mollusca, Gastropoda, Neogastropoda, Muricoidea, Muricidae
Murex pecten Lightfoot, 1786 shell (12.8 cm tall) - abapertural view (left) & apertural view (right).
Murex troscheli Lischke, 1868 shell (11.8 cm tall) - abapertural view (left) & apertural view (right).
Some info. from Morris & Clench (1975), Paul (1981), Harasewych & Alcosser (1991), and Hill (1996).
The turbinids are common, tropical, herbivorous snails. One of the more visually intriguing turbinids is the star turban. This snail tends to inhabit unconsolidated, fine-grained substrates in moderately deep, low-energy settings. The long spines projecting from the final whorl's keel are throught to help prevent the snail from sinking (a common problem among epifaunal, benthic invertebrates throughout geologic history) and to help prevent predators from easily flipping the shell over.
Classification: Animalia, Mollusca, Gastropoda, Archaeogastropoda, Trochoidea, Turbinidae
Guildfordia yoka Jousseaume, 1888 shell (above & below; 8.3 cm across)
Above: apical view. Below: umbilical view.
Some info. from Morris & Clench (1975), Harasewych & Alcosser (1991), and Hill (1996).
The spider conchs, or lambid snails (often grouped with the true conchs - the strombids), are herbivorous gastropods in tropical photic zone environments, feeding on benthic filamentous algae. Lambids can have large, thick shells that are often quite colorful, especially in the apertural areas.
Classification: Animalia, Mollusca, Gastropoda, Caenogastropoda, Stromboidea, Lambidae (or Strombidae)
Lambis chiragra (Linnaeus, 1758) shell (the chiragra spider conch) (22.5 cm tall) - abapertural view (above).
Lambis chiragra shell - apertural view (above). Note the large, rounded drill hole (1.3 cm diameter) near the left margin of the shell. The boring hasn’t penetrated through the thick shell wall - evidence for an unsuccessful predation event.
Lambis scorpio (Linnaeus, 1758) shell (the scorpion spider conch) (13.5 cm tall) - abapertural view (left) & apertural view (right).
Some info. from Harasewych & Alcosser (1991) and Hill (1996).