Cone Shells: Past and Present

“Cones” or "cone shells" are common names for a large group of marine gastropods, whose shell is shaped like a geometric cone. Current sources say that there are between 500 and 800 species of modern cones. Their classification has been in a state of change during the last decade because of new information based on DNA studies of their soft parts.

Cone shells, which can have beautiful color patterns, have been traditionally very popular among shell collectors. If the species is rare, like the one shown below, specimens can be very expensive to purchase. Conus gloriamaris, the so-called "glory of the sea" is a prime example. About 35 years ago, it was considered to be vary rare, hence it was highly priced and worth thousands of dollars. Then many new specimens were found, and the price went way down, to hundreds of dollars.

Conus glorimaris (height 9 cm), West-Pacific region, both shallow and deep-marine depths.

Cones have their greatest diversity in the Western Indo-Pacific region, but a few species have adapted to warm-temperate (coolish) environments, like that found in southern California. Conus californicus is the only cone found today on the west coast of the United States. It is common as beach drift on southern California beaches in Ventura County. This species also has a fossil record in this same area.

Conus californicus (biggest specimen is 3 cm height, Ventura County beach drift, southern California). These shells have been smoothed somewhat by wave action during transport along a beach.

Ancestral cone shells most likely preyed on marine worms because the majority of living cones are vermivorous, that is to say, they  feed on polychaete worms or other worms. During the Miocene (about 15 to 20 million years ago), it is likely that some cones began to hunt for mollusks and fish. This resulted in an explosive adaptive radiation, with an increasing number of cones resorting to these more specialized feeding strategies. Today, there are some cone shells that have retained ancestral feeding habits by preying on worms, but these cones can resort to feeding on mollusks or on fish. One example is Conus tessulatus. It is known to be able to spray venom near the gills of fish, thereby possibly immobilizing them. This technique, however, is not always successful.

Conus tessulatus (4.5 cm height, Seychelles Island, Indian Ocean), a less-derived (in an evolutionary sense) cone. 

Modern cones have developed more effective techniques of delivering venom to their prey. One way, which is used by C. marmoreus (see photos below) is to use a hollow harpoon-shaped tooth that can be injected into a fish. As soon as the fish is paralyzed, the cone "reels" in the fish. Other cones inject extremely toxic venom, and the fish is paralyzed almost immediately.

Conus marmoreus (7.5 cm height) Indo-Pacific region. This a common cone shell, whose shell is thick and heavy. 

Cone toxins are aptly named conotoxins, which are complex cocktails of neurotoxic disulfide-rich peptides. Some of these cone toxins are lethal to humans, thus you should never handle a live cone.

Conus textile (6 cm height, Indo-Pacific region, shallow depth). This is a "deadly" cone, which injects its victims via sharp darts.

Conus geographus (height 9 cm, Indo-Pacific region, shallow water). This cone is well known for its very toxic venom, and some say it is the "number one" most toxic cone. Even predators of mollusks avoid this shell! As a result, the shell of C. geographus is light and thin, unlike nearly all other cone shells.

Cone shells have a fossil record extending back to the Eocene, about 50 million years ago. They had a cosmopolitan (globally widespread) distribution at that time, including occurrences in southern California, southwestern Oregon, and southwestern Washington. Eocene cones are smaller in shell size than most modern cones.

Conus californianus (1.7 cm height, middle Eocene Tejon Formation, southern California). The drill hole in this shell was most likely made by a boring gastropod, belonging to the noticed family.

Conus cowlitzensis (3.6 cm height, late middle Eocene Cowlitz Formation, southwestern Washington). This species is similar morphologically to C. californianus and, together, they likely form a lineage.

Colorful Land Snails

Ancient land snails (air-breathing terrestrial pulmonate gastropods) originated during the Carboniferous Period, probably about 310 million years ago, which was about 165 million years after the first marine gastropods appeared.

More-modern land snails, like those mentioned below, are rare before the Cretaceous but are more plentiful in Cenozoic age (post- 66 million years ago) deposits. As fossils, they are useful to geologists because they are excellent indicators of the terrestrial environment, but their shells are susceptible to having been transported by streams into the marine environment. 

Many modern-day, air-breathing land snails from the tropics have intricate color bands on their shells. Unfortunately, color bands of both terrestrial (and marine shells) are only rarely preserved by fossilization.

The biggest shell is 3.5 cm in height.

Liguus virgineus (Linnaeus, 1758), also called the "rainbow snail" or "candy-stripes snail" air-breathing pulmonate is restricted to the islands of Haiti and Dominican Republic in the Caribbean Sea. They live in trees, thus they are arboreal. They feed on moss, fungi, an microscopic algae that cover the bark. In recent years, they have been over harvested for shell-craft trade. Also, the destruction of forests have become a major threat. The background color of the shell is creamy white, with narrow bright spiral stripes of red, green, blue, yellow, and purple. The slug-like animal itself is brown with black streaks. Genus Liguus belongs to family Orthalicidae.

Both shells are 3.5 cm in height.

 Amphidromus perversus (Linnaeus, 1758) is another tree snail, but its genus belongs to family Camaenidae. It lives in eastern India to northern Australia and especially in Indonesia (e.g., Sumatra, Java, Bali). The two specimens shown above display the asymmetry in shell coiling, which is common among this species. In fact, some populations simultaneously include the left-hand shell coiling (sinistral) and the right-hand shell coiling (dextral). This is a rare biologic phenomenon, and the reasons for it are still being researched. There is also much color variation among this species and its subspecies.

2.7 cm height

Helicostyla roissyana (Férussac, 1840) is the "chocolate-swirl" snail. It is another air-breathing land snail, but it belongs to family 
Bradybaenidae. This snail is endemic to the Philippines. 

The largest shell is 3.2 cm height.

Helicostyla annulata (Sowerby, 1841) is a tree snail, belonging to family Bradybaenidae. The unbounded  yellow to pale-yellow forms are shown here, but there is also a banded form. Helicostyla annulata is common in the Philippines.

                    

   

Ryssota ovum Valenciennes, 1854 is a tree snail restricted to rain forests in the Philippines. It can also live in branch and leaf debris at the tree base. This species is large sized, and the specimen shown here is 7 cm in diameter. The common name of this snail is the "Polished Muffin Snail." Some people consider the meat of this snail to be a delicacy, and its shell is used as a water vessel. The genus belongs to family Helicarionidae.