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.