Among the most interesting predators are poisonous cone shells, which feed on vertebrates or other invertebrates (depending on the species). When Conus senses presence of its prey, a single radular tooth slides into position at the tip of the proboscis. When the proboscis strikes prey, it expels the tooth like a harpoon, and the poison tranquilizes or kills the prey at once. Some species can deliver very painful stings, and the stings of several species are lethal to humans. The venom consists of a series of toxic peptides, and each Conus species carries peptides (conotoxins) specific for the neuroreceptors of its preferred prey.

Pictured is Conus milneedwardsi, commonly known to collectors as the Glory of India.

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Chitons are mollusks belonging to the class Polyplacophora. They are mostly flattened with eight dorsal, limy plates. This is where they get their class name from. (Polyplacophora means “bearing many plates.”) These plates overlap posteriorly and are typically dull in color to blend in with their surroundings (though this is not always the case). Most chitons rarely grow larger than 5 cm and the largest rarely ever exceed 30 cm. They’re usually found stuck onto rocky surfaces in the intertidal zone, but some have been found at much greater depths. If a chiton gets detached from its rock, it can roll up like an armadillo for protection.

Shown is the mossy chiton (Mopalia muscosa), whose mantle is covered in defensive hairs and bristles.

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Pearl formation in mollusks is actually a sort of defense mechanism. Pearls are formed when a bit of sand, grit, or any foreign object makes its way between a mollusk’s mantle and shell. The clam recognizes the object as an irritant and coats it in layers of nacre (what the inside, pearlescent part of clam shells are made out of), making a larger, but less rough and prettier version of the intrusive object.

The round pearls you see used in jewelry are cultured by humans inserting small, perfectly round objects into a certain species of freshwater oysters to make them produce perfectly spheroid pearls. It’s essentially an art of perpetually annoying the oysters to have them produce beautiful things.

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Harp shells (such as Harpa major, pictured here) are so called because of the smooth, evenly spaced ridges that characterize their shells, resembling the strings of harps. Harpa major is a nocturnal gastropod that burrows into sandy substrate in tropical waters. Similar to how a lizard can detach their tails when threatened, harp shells can remove parts of their foot to aid in escape from a predator.

Photos © Teresa Zubi

The dog whelk (Nucella lapillus) has been the subject of a number of scientific studies regarding the effects of pollutants on mollusks’ reproductive development. Tributyltin (TBT), a chemical commonly used as a molluscicide on boats and marine structures, has been directly linked to imposex (females developing a penis) in the dog whelk. Imposex in mollusks such as the dog whelk can lead to reproductive failure by removing a means for the animal’s eggs to leave its body. This discovery from the mid-1980s has helped phase out the use of TBT on smaller ocean-going vessels, but tributyltin can still be used on vessels longer than 25 m in length under the assumption that these vessels will be out in open water, where the chemical can be diluted before it reaches vulnerable near-shore mollusks.

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Nudibranch species, Phyllodesmium kabiranum

Photo © Teresa Zubi

Nudibranch species, Phyllodesmium crypticum

Photo © Teresa Zubi

Nudibranch species, Flabellina rubrolineata

Photo © Johanna Gawron

Transparent octopus (Vitreledonella richardi)

Photo by David Wrobel