Distribution

Most representatives in tropical zones, some also in subtropical and temperate zones of the Indian and Pacific Oceans. Conus mediterraneus (= C. ventricosus) the only species in the Mediterranean.

Biology

Cone shells (Conidae) are a group of predatory marine snails. This group has not yet been divided into various genera, so that all of the approximately 300 species are included in the genus Conus.

Cone shells, like their close relatives the Turrids (Turridae), Mitre shells (Mitridae), Cytharidae and Auger shells (Terebridae), have developed an unusual venom apparatus for catching prey. However, only Cone shells are known to have caused envenoming in humans.

The shell of the Conidae is in the form of a rolled cone. There is a slit-like opening on the long side through which the animals evert their foot. The larger species, such as C. geographus, reach a length of up to 15 cm. With their often strikingly beautifully patterned shells, Cone shells are highly prized among shell collectors.

Cone shells live in shallow water, including coastal zones, especially reef areas, where they conceal themselves in crevices or bury themselves in the sand during the day. Only at dusk do they start appearing for their nightly hunt.

They kill their prey using harpoon-like modified "teeth" on the radula – an organ that these mollusks use to ingest and shred food. The hollow venomous harpoons, up to 12 mm in length, are composed of chitin and are barbed at the tip (Fig. 4.81). Several of them are stored in a special sac inside the snail's body. When required, a single harpoon is transported into the animal's gullet, where it is filled with venomous substances from a venom gland and then shot out by the evertable proboscis. Depending on the prey that different Conus species specialise in hunting, the venoms are specifically active against worms, snails or fish. The venoms of fish-eating species, such as C. catus, C. geographus, C. obscurus or C. tulipa, appear to be particularly dangerous for humans. However, envenoming in humans has also been caused by those species that specialise in invertebrate prey, such as C. textile, C. lividus or C. marmoreus.

Newer research shows, that some species like C. geographus or C. tulipa use different venoms for prey catching and for defense (Richard Lewis, oral communication, 2019); the former venoms not acting paralytic as the latter do. In the case of prey catching no harpunes are used, but special 'nirvana cabals' are difused into the water inducing a strong calming effect on preyfish. The snail then can slowly spred the gullet like a net over its meal! The different venoms seem to be produced in various regions of the venom duct and the individual cone shell can decide which venom cocktail is transported into the gullet.

  Fig. 4.80 Conus marmoreus.


  Fig. 4.81 Harpoon of a Conus shell (length approx. 0.8 mm) with attached ligament. The harpoon consists of a rolled-up chitinous sheet and is hollow inside.

Risk

Envenoming is rare but dangerous. Kohn (1963) lists a total of 37 cases since the beginning of the 18th century from the Pacific Rim (one from the Seychelles). 10 were fatal; 5 of these fatalities were caused by C. geographus, 2 by C. textile and the remaining 3 by unidentified species. Furthermore, cases of severe envenoming were recorded to have been caused by C. omaria and C. tulipa and mild envenoming by C. obscurus, C. catus, C. imperialis, C. lividus, C. quercinus, C. sponsalis, C. marmoreus, C. pulicarius, C. litteratus and C. aulicus.

Accidents occur when live snails are handled (snail collectors!). It is not even necessarily safe to pick up these animals by their rear end, as the everted proboscis is very flexible and can be directed backwards. Some species, such as C. geographus, are easily provoked to sting in defence. The venomous harpoons can easily penetrate clothing, and thus it is quite possible that a Cone shell placed in a trouser or shirt pocket could lead to envenoming.

Literature (biological)

Cleland and Southcott 1965, Endean et al. 1974, Halstead 1988, Kohn 1963, McMichael 1971, Olivera et al. 1988, Stanisic 1987, Sutherland  1983, Salvini-Plawen 1970, Williamson et al. 1996, Cruz and White 1995

Illustrated Conidae Checklist