Conus

Conus

Languages: English

Description

Morphology

There are anatomical and physiological differences between the major groups of cone snails as a result of their different feeding mechanisms. However, in general, all cone snails have an elongated tube known as a siphon, which they use to detect the environment around them. Their venom is produced in the tubular venom duct and expelled into the proboscis by the contraction of a muscular bulb at the basal end of the venom duct. The proboscis also contains a radular tooth which is used as both a harpoon and disposable hypodermic needle through which the venom is delivered to the prey.  Once the venom has been injected, the prey is immobilized almost instantaneously and engulfed by the cone snail (Halai and Craik 2009).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Physiology

Each of the roughly 500 Conus species produces 100-200 venom peptides, with little overlap between species (Olivera 2002). Conus venom research has been reviewed by Olivera (2002), among others.

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Taxon Biology

The genus Conus includes more than 500 species of marine snails, all of which are venomous predators. These snails inject venom into their prey by harpooning them with a disposable hollow tooth through which the venom is channeled (Olivera et al. 1990; Olivera 2002). 

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Ecology

Habitat

Kohn (1983) investigated  the microhabitat factors affecting Conus abundance and diversity on coral reefs. He concluded that the portions of reefs most favorable for Conus have >20% cover of algal-bound sand and <20% living coral. The former microhabitat offers diurnal shelter and dense prey populations. Living coral, in contrast, harbors few suitable prey organisms and, in fact, contact with it elicits a strong avoidance response by Conus (Kohn 1983).

Most familiar Conus species live in relatively shallow waters, but many (probably including many still undescribed species) live below 150 m (Olivera 2002).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Ecology

Conus snails are among the major predators in tropical reef communities and have adapted to nearly every type of tropical marine habitat (Olivera et al. 1990). Although most Conus species prey on only a few (or even a single) species, collectively, they feed on at least four or five different phyla. One group of species feeds only on other mollusks; several hundred other species kill and eat marine worms (mainly polychaetes, but also echiuroids and hemichordates). The 50 or so species that are specialized on killing and eating fishes (first described by A.J. Kohn (1956)) are the only snails known to kill and eat vertebrates (Olivera et al 1990). Conus californicus is unusual in that it has a very broad diet, as well as a temperate distribution (Stewart and Gilly 2005).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Distribution

Conus occurs throughout the tropical and subtropical oceans but is most diverse in the Indo-West Pacific region (The Conus Biodiversity Website, http://biology.burke.washington.edu/conus/index.php). Of the roughly 500 extant Conus species, more than 300 are found in the Indo-Pacific tropics (Kohn 2001). In a study in Papua New Guinea, Kohn (2001) found the numbers of co-occurring Conus species exceeded those of any other known reefs by a factor of one-third or more. Kohn notes that the northeast coast of Papua New Guinea is known to be a biodiversity "hot spot" for many groups of marine benthic invertebrates (Kohn 2001 and references therein).

Although most Conus species have tropical or subtropical distributions, there are a few temperate species (Olivera 2002). Conus californicus, for example, is endemic to the North American Pacific coast (Stewart and Gilly 2005).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Reproduction

Sexes are separate in Conus and the male has an extendable penis (Kohn 1959).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Evolution and Systematics

Systematics and Taxonomy

Duda et al. (2001) undertook a molecular phylogenetic study of Conus to address the evolution of different feeding specializations within the genus. They concluded that feeding on errant (i.e., non-sedentary) polychaete annelid worms was probably the ancestral character state for this group. Mollusc-eating appears to have arisen only once in this group. Fish-eating may have arisen several times, but the phylogeny was not sufficiently well resolved to draw any strong conclusion on this question. Type of prey consumed appears to be a relatively conservative trait, with diets having shifted only rarely since the first major Conus radiation in the Miocene (Duda et al. 2001).

Conus provides one of the few known examples of a marine "species flock" (Duda and Rolan 2005). (A species flock is a monophyletic assemblage of endemic taxa (i.e., taxa found nowhere else) that arose rapidly in a small geographical area--classic examples being Darwin's finches in the Galapagos and African rift lake cichlid fish in East Africa).  The Cape Verde Archipelago has 47 endemic and just three non-endemic Conus species. Based on a molecular phylogenetic analysis, Duda and Rolan conclude that the contemporary endemic Conus species in the Cape Verde islands are the evolutionary descendants of two separate colonization events. The authors suggest that the life history of the Cape Verde Conus may have facilitated their isolation through evolutionary time: Although, overall, ~75% of Conus species whose mode of development is known have an obligate planktonic, feeding larval stage in their life history, this is not the case for eastern Atlantic species (including all the Cape Verde Conus), nearly all of which are direct devopers, meaning they have no dispersing larval phase (Duda and Rolan 2005 and references therein).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

Relevance

Risk Statement

Stings from several Conus species have been reported to cause human fatalities, although only fatalities from C. geographus have been confirmed; it is estimated that a quarter of stings from C. geographus may be fatal to humans, but such encounters are fortunately rare (Fegan and Andresen 1997). About 3 dozen recorded human fatalities from C. geographus stings have been recorded in the medical literature (Olivera 2002). Symptoms from a cone snail sting vary somewhat depending on the species. There may be extreme pain, or a spreading numbness followed by paralysis (McIntosh and Jones 2001). In general, the venoms of fish-hunting species are more lethal to vertebrates (Kohn et al. 1960, cited in Olivera 2002).

Several toxic peptides from Conus species are widely used as research tools and active efforts are underway to screen Conus toxins for potential development as useful drugs. Among the possible conditions being considered as potential targets for these new drugs are chronic pain, epilepsy, cardiovascular disease, psychiatric disorders, movement disorders, cancer, and stroke (McIntosh and Jones 2001). Conus-derived products might also be useful as neuromuscular blocking agents in anesthesia. The appeal to researchers of the rich diversity of cone snail toxins is the novelty and/or specificity with which they target a given receptor or ion channel (McIntosh and Jones 2001).

Author(s): Shapiro, Leo
Rights holder(s): Shapiro, Leo

References

Chivian, E., Roberts C. M., & Bernstein A. S. (2003).  The Threat to Cone Snails. Science. 302, 391.
Duda, T. F., & Rolan E. (2005).   Explosive radiation of Cape Verde Conus, a marine species flock. Molecular Ecology. 14, 267-272.
Duda, T. F., Bingham J. - P., Livett B. G., Kohn A. J., Massilia G. R., Schultz J. R., et al. (2004).  How much at risk are cone snails?. Science. 303, 955.
Duda, T. F., Kohn A. J., & Palumbi S. R. (2001).  Origins of diverse feeding ecologies within Conus, a genus of venemous marine gastropods. Biological Journal of the Linnean Society. 73, 391-409.
Fegan, D., & Andresen D. (1997).  Conus geographus envenomation. The Lancet. 349, 1672.
Halai, R., & Craik D. J. (2009).  Conotoxins: natural product drug leads . Natural Product Reports. 26, 526-536.
Jr., D. T. F., & Kohn A. J. (2005).  Species-level phylogeography and evolutionary history of the hyperdiverse marine gastropod genus Conus. Molecular Phylogenetics and Evolution. 34, 257-272.
Kohn, A. J. (1956).  Piscivorous gastropods of the genus Conus. Proceedings of the National Academy of Sciences USA. 42, 168-171.
Kohn, A. J. (1959).  The Ecology of Conus in Hawaii. Ecological Monographs. 29, 47-90.
Kohn, A. J. (1983).  Microhabitat factors affecting abundance and diversity of Conus on coral reefs. Oecologia. 60, 293-301.
Kohn, A. J., Saunders P. R., & Wiener S. (1960).  Preliminary studies on the venom of the marine snail Conus. Annals of the New York Academy of Sciences. 90, 706-725.
McIntosh, J. M., & Jones R. M. (2001).  Cone venom-from accidental stings to deliberate injection. Toxicon. 39, 1447-1451.
Nelson, L. (2004).  Venomous snails: One slip, and you're dead.... 429, 798-799.
Olivera, B. M. (2002).  Conus venom peptides: relections from the biology of clades and species. Annual Review of Ecology and Systematics. 33, 25-47.
Olivera, B. M., Rivier J., Clark C., Ramilo C. A., Corpuz G. P., Abogadie F. C., et al. (1990).  Diversity of Conus Neuropeptides. Science. 249, 257-263.
Stewart, J., & Gilly W. F. (2005).  Piscivorous behavior of a temperate cone snail, Conus californicus. Biological Bulletin. 209, 146-153.