Conus

Diversity

Conus is one of the most diverse and species rich genera of marine animals (with over 500 extant species) and have been highly successful since appearing around 55 million years ago. Most of the diversity is accounted for morphologically, as they live in similar ecological niches and have similar lifestyles (Duda and Kohn, 2005; Kohn 1959). Species diversity in certain geographic areas is less than that in others. Cone snails in the northern Red Sea, for example exhibit much lower rates of diversity than those in the Indo-Pacific region (Zauner and Zuschin, 2016). Diversity can be seen in diets across species, which also relates to the number of peptides in venom produced in different species (Remigio and Duda, 2008).

Geographic Range

Members of the genus Conus are found in tropical waters around the world. Nearly 60% of described species are in the western Pacific Ocean and tropical parts of the Indian ocean. Another 90 species are found in the eastern Pacific Ocean, as well as eastern and western areas of the Atlantic Ocean (Duda and Kohn, 2005). Cone snails have been studied in many places across this range including Hawaii, Papua New Guinea, and the Northern Red Sea (Kohn, 1959; Muttenthaler et al., 2012; Zauner and Zuschin, 2016).

• Biogeographic Regions
• indian ocean
• atlantic ocean atlantic ocean
• pacific ocean pacific ocean

Habitat

There are two main types of habitats where Conus gastropods are found. These are: places where low tide exposes them to air at times, and places where the snails are submerged in water at all times. In both cases, the snails are found on or near coral reefs (Kohn, 1959). Across the globe, Conus species are found predominantly on coral reefs, but also inhabit other niches around reefs. In the Northern Red Sea, reef flats have the highest population density of Conus , while subtidal reefs and subtidal sand areas see fewer species (Zauner and Zuschin, 2016). A study done in Papua New Guinea had similar results; a total of 422 live snails of 30 different species were observed on only ten reefs in the area (Muttenthaler et al., 2012).

• Habitat Regions
• tropical tropical
• saltwater or marine saltwater or marine

• Aquatic Biomes
• reef reef
• brackish water brackish water

• Other Habitat Features
• intertidal or littoral intertidal or littoral

Systematic and Taxonomic History

This genus was described by Linnaeus in 1758. Although there are no synonyms for this genus, there are several cases of synonymy among species and subspecies (Roskov, et al., 2017). Since being described, all cone snails have traditionally been placed in this single genus. Many studies have been done, and revised and updated phylogenies are continuously being published. In addition, multiple studies agree that one species, Conus californicus , is the sister taxa to all other cone snails. Some studies even suggest putting that single species into its own genus: Californiconus (Puillandre, et al., 2015; Puillandre and Tenorio, 2017). Of the hypotheses in the field, some are in favor of keeping Conus as one genus, and others that say there are as many as 127 genera, and many more subgenera. Puillandre, et al. support a system of four genera and 71 subgenera for this group. This system is well supported by both morphological and molecular data and is popular in the field. Many of the hypotheses that have been suggested regarding Conus use only shell and radula variation data, which alone is not a good indicator of evolutionary relationships (Puillandre, et al., 2015).

Physical Description

The most notable distinguishing character of Conus gastropods is their cone-shaped shells, which can be a variety of colors and patterns. An important trait to this group is a proboscis that aids in the injection of venom into prey. Along with the proboscis, the radula/radular teeth function to immobilize prey by actually going into the skin and releasing venom (Stewart and Gilly, 2005). Adult Conus species have shells between 33 and 37 millimeters in length. Juveniles are similar in appearance to adults, and two days after hatching are already crawling on their muscular foot. There is no sexual dimorphism, as the only physical difference is that males of this species have a penis that extends from the body (Kohn, 1959).

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry
• venomous venomous

• Sexual Dimorphism
• sexes alike

Reproduction

When Conus species mate, they do so throughout the year and both sexes mate with multiple different individuals in their lives. The snails will secrete pheromones that attract mates towards them, and a male will approach a female. It is important to know that Conus do not follow mucus trails to sense and find mates. As mating begins, the male goes to the female’s right, anterior side where he climbs onto the shell and extends his penis. He begins to touch and sense the shell while moving to the posterior end of the female’s shell. When he reaches the end, the penis is used to sense and find the opening to the mantle cavity. The female reproductive structures are near this opening. The male inserts his penis, and the couple remain motionless for 20-25 minutes while insemination occurs. In Conus cingulatus , the male buried himself under the sand, while the female roamed the tank immediately following mating. These and other systems are less studied across Conus , but other species from family Conidae and other closely related families ( Buccinidae and Fasciolariidae ) have been studied and have shown comparable results. It is therefore reasonable to assume that this system is true across most of Conus (Cosel and Kohn, 2013; Cruz, et al., 1978).

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Species of Conus will mate and spawn throughout the year, and egg cases are laid in masses containing many eggs. Females of C. geographus have a noticeable increase of oviposition in the month of April. Generally, across all Conus , as females get older their shell's annual growth rate decreases and rate of ova production increases. This allows more energy to be put into reproduction. In C. geographus , females produce about 6,000 ova by the time they are ten years old. Development time, that is from oviposition to hatching, is species specific and varies across Conus . In Hawaiian species, this time typically ranges from 11-26 days (Cruz, et al., 1978; Perron, 1981; Perron, 1983).

• Key Reproductive Features
• iteroparous iteroparous
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous

Most of the maternal reproductive energy is focused towards the egg cases in which embryos are laid. Around 50% of energy designated to reproduction is used in making these egg cases, consisting mainly of proteins. This makes sense when considering certain species make cases of various thickness and strength. The species that spend the most time developing will have thicker egg cases, and the species that develop the fastest have thinner egg casings. This provides protection from predators, and aids in prevention of desiccation (some egg cases may be laid in places that are exposed to air in low tide). The remaining 50% of reproductive energy is used towards nutrition for developing embryos (post-fertilization, pre-oviposition), as well as providing food for offspring (post-hatching, pre-independence). Although there is information that Conus begin mating at about two years old, there is little knowledge regarding how long parents will care for their offspring (Perron, 1981; Perron, 1983).

• Parental Investment
• female parental care female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• pre-independence
  • provisioning
    • female
  • protecting
    • female

Lifespan/Longevity

Conus gastropods live for a relatively long time. Most species live to about 10 years, with some species exceeding that. One species, Conus pennaceus is typical in that their lifespan is limited to around 10 years, while Conus quercinus and C. flavidus live much longer; the former reaching an age of 17 while the latter reaches 20 (Perron, 1986).

Behavior

Conus species are social, motile gastropods that are primarily active at night and dormant during the day. During daytime, these snails hide in algae or under rocks and coral. This happens because prey is also more active and plentiful in the environment during the night, so the mollusks must wait until then to feed. Another reason is that almost all of the smaller species are unable to hold themselves in strongly moving waters, such as waves, and limit their activity to after the tide has receded. In the lab, Kohn observed snails active at night even while the habitat was lit. He suggested that it was the natural daily rhythm of the organisms to be active at that time, regardless of the lights (Kohn, 1959).

These snails have a proboscis that is very important for feeding and reproductive behaviors. This organ is used for sensing the environment (finding food) and has a modified radular tooth that is used to inject a fast-acting venom into prey (Puillandre, et al., 2015). The proboscis is used to sense species-specific chemical cues and physically touching the mate during mating (Kohn, 1961). Snails also respond to touch.

Conus species exhibits a high amount of parental care to young, with anywhere from 30.9% to 52.4% (depending on species) of maternal energy going to care of offspring (Perron, 1986).

• Key Behaviors
• nocturnal nocturnal
• motile motile
• sedentary sedentary
• daily torpor
• social social

Communication and Perception

Cone snails have a highly developed chemosensory system. This system is primarily for feeding, and captive specimens were observed immediately moving towards food that was placed in the habitat. This chemosensory system is also important to reproduction. Prior to mating, Conus snails use the tip of the proboscis to detect chemicals in the water secreted by members of the opposite sex, and move towards them (Kohn, 1961).

• Communication Channels
• tactile tactile
• chemical chemical

• Other Communication Modes
• pheromones pheromones

• Perception Channels
• tactile tactile
• chemical chemical

Food Habits

There are three main feeding types in Conus . There are piscivorous, vermivorous, and molluscivorous species, and some, such as C. flavidus , that eat enteropneust hemichordates Order Enteropneusta . Among the vermivorous species, many consume only polychaete worms Class Polychaeta . Some species, such as C. pennaceus , are molluscivorous and feed on other marine gastropods, including other Conus species. The piscivorous species, such as C. californicus prey on prickleback fish ( Cebidichthys violaceus and species of Xiphister ) and others (Remigio and Duda, 2008; Stewart and Gilly, 2005).

In addition to these types of feeding there are two main feeding strategies. In Conus striatus , the radular tooth at the end of the proboscis remains attached after injecting prey with venom. The proboscis then retracts and pulls prey into the mouth. In Conus abbreviatus and Conus ebraeus , the radula tooth is left in the prey and the snail moves toward the prey, while expanding its mouth to ingest it. In C. pennaceus , up to six radular teeth may be left in a single victim. In C. californicus and other piscivores some do not inject the radula at all, and others that will attack the prey with its proboscis multiple times (Kohn, 1959; Stewart and Gilly, 2005).

In molluscivorous C. pennaceus and Conus textile , when the prey has a small shell it will be ingested and regurgitated. In large-shelled prey, the venom is injected (usually in the foot) and loosens the body of the organism from its shell, and the soft body is consumed (Kohn, 1959).

• Primary Diet
• carnivore carnivore
  • piscivore piscivore
  • molluscivore molluscivore

• Foraging Behavior
• stores or caches food stores or caches food

Predation

This group is not highly preyed upon, but it is likely that both parrot fish ( Family Scaridae ) and zebra eels ( Gymnomuraena zebra ) prey on Conus . There are also Conus species that prey on other gastropods including other members of their genus; these include C. pennaceus and C. textile . In the lab, Cymatium gastropods and Asterope seastars preyed on Conus , with reason to believe this happens in nature as well. In the past, Conus have been preyed upon by Menippe mercenaria and it is theorized that this group significantly influenced the evolution of Conus . In addition to this species, other crabs are known to tear the egg-cases and prey on developing embryos (Kohn, 1959; Perron, 1981; Kosloski and Allmon, 2015).

• Anti-predator Adaptations
• aposematic aposematic

Ecosystem Roles

As predators, Conus play a big role in their ecosystems. They prey on fish, polychaetes, even other mollusks. They are also a food source to the groups that prey on them. With few predators, Conus is an extremely successful group (Kohn, 1959).

In these snails, there is a very interesting mutualistic relationship between actinomycetes. In this genus, there were high amounts of these bacteria, a total of 229 that were morphologically distinct across three species of Conus . The goal was to gain new information on bioactive bacteria in hopes of finding better drugs and medicine, although at the time of the study they were unable to determine the association between these bacteria and the venom of this genus (Peraud, et al,. 2009).

Economic Importance for Humans: Positive

Although small in size, Conus species have been very important to humans throughout history. There is a global market established for the trade of Conus shells, that range from amateur collectors to professional traders. There are also local markets that sell to tourists and support the economy, or just individual households. This group is also sold as a food source in the local markets. To these people, Conus species are important. Conus are also being targeted for drug research more recently, and scientists are looking into ways of creating more effective and less addictive drugs (Peters, et al., 2013).

• Positive Impacts
• food food
• body parts are source of valuable material
• source of medicine or drug source of medicine or drug
• research and education

Economic Importance for Humans: Negative

There is only a single known adverse effect this group has on humans. This is that their venom is highly toxic to humans, and some have died from being bitten. The geography cone, Conus geographus , causes most Conus - related human deaths (Peters, et al., 2013).

• Negative Impacts
• injures humans
  • venomous venomous

Conservation Status

There are 632 species of Conus studied in a summary and analysis of conservation status of the genus. According to IUCN Red List, three species are critically endangered. These are: Conus lugubris , Conus mordeirae , and Conus salreiensis of Cape Verde, Africa. Eleven of these species are endangered, including Conus clover , Conus hybridus and Conus Mercator of Senegal, West Africa. 27 are vulnerable, including Conus compressus and Conus thevendarnesis of Australia. Another 26 are near threatened and 87 are data-deficient. The status of the remaining 478 species is of least concern (Peters, et al., 2013).

The main reason Conus are becoming endangered is habitat loss and coastal development. In addition, there is pollution damaging existing habitat. Another contributing factor is that Conus are often accidentally harvested by fisheries (Peters, et al., 2013; Polidro, et al., 2017).

Other Comments

Fossils of Conus have been acquired from the Neogene period and are about 6.6-4.8 million years old. There are over 1,000 described fossil species of Conus , but Hendricks suggests that many are synonymous and the reason for that is their shell morphology and coloration cannot be studied, which prevents accurate classification. These shells do not show any original color patterns under normal light because of their age, however under UV light, Hendricks found that 60% revealed original color patterns. After being photographed in UV light, the image can be photo-edited to show the original color. This is being used in order to more clearly understand fossil mollusks, including those of Conus (Hendricks, 2015).

Additional Links

Encyclopedia of Life

Contributors

Triston Childs (author), Colorado State University, Genevieve Barnett (editor), Colorado State University.

References

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