Introduction
The Neogastropoda is comprised of mostly predatory snails, although a few groups have secondarily evolved to become omnivores, scavengers, detritusfeeders, parasites, and even herbivores. Herbivory is almost certainly an evolutionarily derived condition within the Neogastropoda based on available phylogenetic evidence and the prevalence of carnivory in potential sister groups to the Neogastropoda. This would also be consistent with a much groader trend of increasing levels of herbivory and herbivore diversity in marine ecosystems since the Mesozoic.
Among the carnivorous neogastropods, some actively seek prey (usually polychaetes or molluscs), whereas other graze on colonial animas (e.g., corals and tunicates). Pre subjugation often involves production of chemicals by the carnivore that attacks the prey's nervous system and renders it helpless during feeding. Some neogastropods make anti-coagulants that prevent blood clotting and thus allow the snail to feed for extended perods of time ona prey's blood. Colubrarias are the vampires of the coral reef. The feed on the blood of sleeping fish (See video of Colubraria spp. feeding). Other predatory adaptations include the buccinid whelk strategy of employing the shell lip to either wedge or chip open bivalve prey and muricid ability to bore holes through shelled prey, such as molluscs and barnacles. Recently, several species outside of the Muricidae have been found to bore holes as well, including some members of the Marginellidae and Buccinidae.
Feeding and Ecology
The feeding ecology of two groups in particular, cones and muricids, has been studied in great detail. Both exhibit diverse diets and predation behaviors:
Conidae:
Cone snails are generally divided into three groups: worm hunters (vermivorous), snail hunters (molluscivorous), and fish hunters (piscivorous). Cones (and related turrids) have an internal venom delivery system consisting of a venom duct, where the venom is synthesized and stored, a venom bulb used to transfer venom from the duct, and hollow harpoon-like teeth that are used like hypodermic needles for injecting the prey with venom.
The hunting methods of cone snails are extremely exciting to watch. Cone snails that hunt fish use two different methods to capture their prey. In the one method, the mouth of the snail is expanded to form a wide net that engulfs the fish, which are then injected with a harpoon-like tooth filled with venom (See vide of Conus geographus eating clownfish). In the other method, a long distensible proboscis is used to extend a hollow harpoon like tooth filled with venom to inject into the fish (See video below of Conus monachus eating goldfish).
Also shown below is video footage of Conus californicus building an egg sac on the wall of an aquarium.
Muricidae:
Another neogastropod group, the Muricidae, are well known for their ability to bore through the shells of invertebrate prey using a chemical secretion from a gland in the foot (accessory boring organ) and a rasping tooth in the snout-like proboscis (radula).
Hole boring as a mode of predation poses a number of challenges for the predator. Both problems are related to the fact that drilling is extremely time consuming. Phyllonotus and Chicoreus can take up to a week or more to complete a drillhole and consume bivalve prey under ideal lab conditions, and Nucella lamellosa can take 5 days to drill even a thin-shelled mussel. This while engaged in the act of hole boring, much of the animal's energy is devoted to work and maintenance instead of actual food consumption, which is necessary for growth and reproduction.
A more lethal problem for hole boring snails is exposure to enemies while boring. Predatory crabs, fish, octopods, and other gastropods are common in environments where muricids are found, and dead broken or drilled shells of muricids shows that they are frequent targets of predation themselves. Because hole boring requires the snail to sit out in the open for up to a week (the entire time exposed to these predators), muricids take considerable risks every time they feed. Taking too long to drill and consume prey may also increase the odds that competitors will be attracted to the kill site and steal all the spoils.
Thus, animals that find ways to feed more rapidly and efficiently should, therefore, possess an edge over conspecifics in lifetime reproductive output. Not surprisingly, some muricids have evolved the ability to feed more rapidly by using other modes of predation, including the use of toxins, chipping of bivalve prey with the shell lip, and wedging open bivalves and barnacles with a labral spine. Some have forsaken predation altogether and feed on carrion or eggs of other snails.
References
Photo images credited to Kerry Matz
Video images credited as follows:
Conus:
* Conus geographus eating Nemo
* Conus Manachus eating goldfish
(Credit the Olivera Laboratory and KUHZ)
Buccind:
* Colubraria muricata closeup of feeding on blood of fish
* Colubraria muricata fish escaping
* Colubraria nitidula approaching fish with proboscis
* Colubraria muricata approaching fish with proboscis
(Credit Marco Oliverio and Stefano Schiaparelli)
Use of video footage or images is not allowed without the written permission of the Author Stefano Schiaparelli steschia@dipteris.unige.it
Building Egg Sac:
Conus:
* Conus californicus building egg sac on aquarium wall
* Conus californicus inserting egg sac
(Credit Estuardo Lopez Vera)
For permission to use images or videos for species other than Colubraria, please contact Baldomero Olivera, olivera@biology.utah.edu