Where is mollusks found

The primarily herbivorous chitons have a well-developed radula. Their nervous system is a series of ladder-like nerves and only a few species have poorly developed ganglia. Chitons are found only marine environments. They are most commonly found in tide pools and rocky intertidal zones. Chitons can tolerate the harsh conditions of these habitats where ocean and land meet. Gastropods are the most diverse group of molluscs Fig.

The ones we usually think of are snails and slugs. Most gastropods have a calcareous shell protecting the soft-bodied animal inside. Some gastropods, such as sea slugs, sea hares, and garden slugs, lack a shell or have a reduced shell buried in the folds of their mantle. Most creep about on a flattened foot, but some swim, using extended folds of their mantle as fins.

Most snails and terrestrial slugs are herbivorous. They use their radula to scrape algae from surfaces Fig. For this reason, gardeners consider snails and slugs to be pests.

Some gastropods are carnivores, stalking other snails, worms, and fish for food Fig. The colorful and striking nudibranchs contain many carnivorous specialists. Many nudibranchs feed on only one type of sponge; their body coloration and their eggs are patterned to blend in with their prey. Other gastropods use their radula and acidic secretions to bore holes in shells and prey on other molluscs.

In the Hawaiian Islands, the terrestrial cannibal snail Euglandina rosea ; Fig. The giant East African land snail is considered to be an agricultural pest and is also known to be a carrier of the parasitic nematode rat lungworm Angiostrongylus cantonensis ; Fig.

Unfortunately, the cannibal snails also predated native land snails, nearly driving them to extinction. Marine and freshwater gastropods breathe using ctenidia or gills. In many of these gastropods the ctenidia are protected within the mantle cavity. This distinctive trait makes nudibranchs an easily identifiable group of molluscs.

Terrestrial slugs and snails, by contrast are primarily in a subgroup known as the pulmonates that actually have a mantle cavity that has become connected to the circulatory system vascularized to function as a lung. Gastropods move by contracting their muscular foot in a series of waves to creep forward. These trails also provide chemical communication among gastropods. The cannibal snail, for example, tracks its prey by following the mucus trail left behind.

The gastropod nervous system includes bodily nerves and anterior ganglia with relatively sophisticated sensory systems, including light receptors and well developed chemosensory abilities. The bivalve molluscs get their name from the two door-like valves or shells that make up their exoskeleton Fig. Foot size varies among marine bivalves. Clams have a muscular hatchet-shaped foot for moving about and for burrowing in mud or sand Fig.

They swim in short bursts by jet propulsion, clapping their shells together and forcing water out the rim. Bivalves are more enclosed by their shells than other molluscs. Water enters and leaves a bivalve by way of two tubes called siphons. One siphon takes in water while the other expels water and waste. The water taken in contains oxygen and food particles. Most bivalve species acquire energy and nutrients through filter feeding. Filter feeding or suspension feeding is the process of ingesting water and filtering out food particles.

Invertebrate examples of filter feeders include sponges, corals, and bivalve molluscs. As water is taken into the body, it flows across the gills. Oxygen O 2 and carbon dioxide CO 2 are exchanged between the circulatory system and the water. Mucus on the gills traps microscopic food particles, and tiny hairlike cilia move the food-laden mucus toward the mouth.

Liplike structures called palps help sort the food and direct it into the mouth. Bivalves do not have a radula Fig.

The food suspended in mucus moves through the digestive organs, which break it down and absorb it. Bivalves such as clams, oysters, and scallops are valuable as food.

They make up a major share of the marine invertebrate seafood industry. Bivalves should not be eaten when the water in which they grow becomes polluted with chemicals or disease organisms. At certain times of year, microscopic organisms called dinoflagellates multiply rapidly in nearshore waters. Toxic substances produced by dinoflagellates can concentrate in the clams and oysters that use them as food.

Although the bivalves are not harmed, the toxin can attack the nervous system of humans who eat the tainted shellfish. Toxic shellfish poisoning can be fatal to humans. A pearl forms as coats of nacre build up around the foreign particle.

Cultured pearls used in jewelry are produced when farm-raised oysters are intentionally seeded with foreign particles to stimulate the production of nacre. The cost of pearls varies with size, color, and luster. Before plastic came into use, the shells of bivalves were commonly used to make buttons. The material known as mother-of-pearl is harvested from the nacre of mollusc shells. The cephalopods are molluscs with large heads and tentacles. Examples of cephalopod molluscs include squid, octopus, cuttlefish, and nautilus Fig.

Most cephalopods are relatively small. But the giant octopus Enteroctopus sp. The giant squid, the largest invertebrate, reaches lengths of 15 m. The foot in this group has specialized by dividing into arms that are attached to the head, thus the name cephalopod, meaning head-foot. Like other molluscs, cephalopods have a mantle and mantle cavity that houses the respiratory ctenidia.

The mantle cavity is also used to take in and rapidly expel water to facilitate the jet propulsion swimming mode of most cephalopods. When the mantle closes forcefully, seawater ejected through the siphon propels the animal in short bursts. Both squid and octopus change course by redirecting their siphon.

They steer by pressing their arms together and can use their speed to elude an attacking predator. Molluscs are further classified into seven major groups and Sydney has representative from five of these.

The main groups found in Sydney are gastropods, bivalves, cephalopods, chitons, and also a minor group, the aplacophorans or spicule worms. Molluscs can be found in marine, terrestrial and freshwater environments. Although extremely diverse, molluscs have some common characteristics such as a soft, unsegmented body, a muscular foot or tentacles and a mantle that can secrete a shell. Most molluscs with shells produce a highly valuable and shiny object: the pearl.

The most desirable pearls are natural pearls, which are formed when a small, foreign object gets stuck inside an oyster. Learn about our collection and study of molluscs; including chitons, clams, mussels, snails, nudibranchs sea slugs , tusk shells, octopus and squid. AMRI brings together scientific expertise and world-class research infrastructure to increase our knowledge of the world around us and inform environmental decision-making for a better future.

Since we have published the results of studies derived from our collections or research that lead to a better understanding of nature and cultures in the Australian Region. Read about our latest discoveries, research expeditions or discover our interesting archive of blog posts. Use our online enquiry form for help with Australian animal identification, natural history and cultural object enquiries. The Lizard Island Research Station is a world-leading supplier of on-reef facilities for coral reef research and education.

The Australian Museum respects and acknowledges the Gadigal people as the First Peoples and Traditional Custodians of the land and waterways on which the Museum stands. The largest bivalve is the giant clam Tridacna gigas , which reaches a length of four feet and weighs pounds. The oldest mollusk is a bivalve, the ocean quahog Arctica islandica , native to the northern Atlantic and known to live at least years; it is also the oldest known animal.

Gastropods and bivalves may be the most common mollusks, but cephalopods the family that includes octopuses , squids , and cuttlefish are by far the most advanced. These marine invertebrates have astonishingly complex nervous systems, which allows them to engage in elaborate camouflage and even display problem-solving behavior—for example, octopuses have been known to escape from their tanks in laboratories, squish along the cold floor, and climb up into another tank containing tasty bivalves.

If human beings ever go extinct, it may well be the distant, intelligent descendants of octopuses that wind up ruling the earth—or at least the oceans! The largest mollusk in the world is a cephalopod, the colossal squid Mesonychoteuthis hamiltoni , known to grow to between 39 and 45 feet and weigh up to 1, pounds.

With the exception of cephalopods, mollusks are by and large gentle vegetarians. Terrestrial gastropods like snails and slugs eat plants, fungi, and algae, while the vast majority of marine mollusks including bivalves and other ocean-dwelling species subsist on plant matter dissolved in the water, which they ingest by filter feeding. The most advanced cephalopod mollusks—octopuses, squids, and cuttlefish—feast on everything from fish to crabs to their fellow invertebrates; octopuses, in particular, have gruesome table manners, injecting their soft-bodied prey with venom or drilling holes in the shells of bivalves and sucking out their tasty contents.

The nervous systems of invertebrates in general and mollusks in particular are very different from those of vertebrate animals like fish, birds, and mammals. Some mollusks, like tusk shells and bivalves, possess clusters of neurons called ganglions rather than true brains, while the brains of more advanced mollusks like cephalopods and gastropods are wrapped around their esophagi rather than isolated in hard skulls.

Even more weirdly, most of the neurons of an octopus are located not in its brains, but in its arms, which can function autonomously even when separated from its body. Mollusks generally reproduce sexually, although some slugs and snails are hermaphrodites, they still must mate to fertilize their eggs. Eggs are laid singly or in groups within jelly masses or leathery capsules. The eggs hatch into veliger larva—small, free-swimming larvae—and metamorphose into different stages, depending on the species.

Because modern mollusks vary so widely in anatomy and behavior, sorting out their exact evolutionary relationships is a major challenge. In order to simplify matters, naturalists have proposed a "hypothetical ancestral mollusk" that displays most, if not all, of the characteristics of modern mollusks, including a shell, a muscular "foot," and tentacles, among other things.

We don't have any fossil evidence that this particular animal ever existed; the most any expert will venture is that mollusks descended hundreds of millions of years ago from tiny marine invertebrates known as "lophotrochozoans" and even that is a matter of dispute.

Examining the fossil evidence, paleontologists have established the existence of two now-extinct classes of mollusk. Somewhat surprisingly, cephalopods have existed on earth ever since the Cambrian period ; paleontologists have identified over two dozen much smaller and much less intelligent genera that plied the world's oceans over million years ago.

Over and above their historical importance as a food source—especially in the far east and the Mediterranean—mollusks have contributed in numerous ways to human civilization. The shells of cowries a type of small gastropod were used as money by Indigenous groups, and the pearls that grow in oysters, as the result of irritation by sand grains, have been treasured since time immemorial.

Another type of gastropod, the murex, was cultured by the ancient Greeks for its dye, known as "imperial purple," and the cloaks of some rulers were woven from long threads secreted by the bivalve species Pinna nobilis. One, the Ohridohauffenia drimica was last seen in in springs feeding the River Drim in Macedonia, Greece and was listed as extinct in Additional surveys have failed to find it again.

The vast majority of mollusks live in the deep ocean and are relatively safe from the destruction of their habitat and depredation by humans, but that's not the case for freshwater mollusks i.