api/deki/files/5084/girl-160172__340.png" title="Boundless" />Contributed by BoundlessGeneral Microcentregalilee.comlogy at Boundless

Class Polyplacophora

Animals in the class Polyplacophora (“bearing numerous plates”) are frequently known together “chitons” and also bear one armor-like, eight-plated dorsal shell. These animals have a broad, ventral foot that is adapted for suction come rocks and also other substrates, and also a mantle that extends beyond the covering in the form of a girdle. Calcareous spines might be current on the girdle to offer defense from predators. Chitons live worldwide, in cold water, warmth water, and the tropics. Many chiton types inhabit intertidal or subtidal zones, and also do not extend past the photic zone. Some types live rather high in the intertidal zone and are exposed to the air and also light for lengthy periods.

You are watching: What are the three classes of mollusks

Figure (PageIndex1): Chiton morphology: The underside the the gumboot chiton, Cryptochiton stellari, showing the foot in the center, surrounded by the gills and mantle. The mouth is visible to the left in this image.

Class Bivalvia

Bivalvia is a class of marine and also freshwater molluscs v laterally compressed body enclosed by a covering in two hinged parts. Bivalves incorporate clams, oysters, mussels, scallops, and numerous other family members of shells. The majority are filter feeders and also have no head or radula. The gills have developed into ctenidia, specialty organs for feeding and breathing. Most bivalves ask themselves in sediment top top the seabed, while rather lie ~ above the sea floor or affix themselves to rocks or other hard surfaces.

The shell of a bivalve is created of calcium carbonate, and also consists the two, generally similar, parts called valves. These space joined with each other along one leaf by a functional ligament that, in conjunction through interlocking “teeth” on every of the valves, forms the hinge.

Figure (PageIndex1): Empty shell of a bivalve: The empty shell of the gigantic clam, Tridacna gigas. Keep in mind the pair that shells that are hinged together, a characteristic of members of the course Bivalvia.

Class Gastropoda

Animals in course Gastropoda (“stomach foot”) incorporate well-known mollusks choose snails, slugs, conchs, sea hares, and also sea butterflies. Gastropoda consists of shell-bearing varieties as well as types with a decreased shell. These animals are asymmetrical and also usually existing a coiled shell. Shells might be planospiral (like a garden hose wound up), generally seen in garden snails, or conispiral (like a spiral staircase), typically seen in naval conches.

The visceral fixed in the shelled types displays torsion about the perpendicular axis on the facility of the foot, which is the vital characteristic that this group, along with a foot that is modified because that crawling. Most gastropods be affected by each other a head through tentacles, eyes, and also a style. A facility radula is provided by the cradle system and also aids in the gulp down of food. Eyes may be absent in part gastropods species. The mantle cavity encloses the ctenidia (singluar: ctenidium) as well as a pair that nephridia (singular: nephridium).

Figure (PageIndex1): Gastropod foot: Gastropods, such together this roman snail, have actually a large foot the is modified for crawling.

Class Cephalopoda

Class Cephalopoda (“head foot” animals) contains octopi, squids, cuttlefish, and nautilus. Cephalopods space a course of shell-bearing animals and mollusks through a decreased shell. They display screen vivid coloration, commonly seen in squids and octopi, i m sorry is supplied for camouflage. All animals in this course are carnivorous predators and also have beak-like jaws at the anterior end. Every cephalopods present the visibility of a an extremely well-developed worried system together with eyes, and a close up door circulatory system. The foot is lobed and also developed into tentacles and also a funnel, which is supplied as the mode of locomotion. Locomotion in cephalopods is helped with by ejecting a present of water for propulsion (“jet” propulsion). Cephalopods, such together squids and also octopi, additionally produce sepia or a dark ink, which is squirted upon a predator to aid in a fast getaway. Suckers are current on the tentacles in octopi and squid. Ctenidia room enclosed in a large mantle cavity serviced by blood vessels, each v its own associated heart. The mantle has actually siphonophores the facilitate exchange that water.

Figure (PageIndex1): Cephalopods: Cephalopods (“head foot”) include this octopus, i beg your pardon ejects a currently of water from a funnel in its human body to propel itself with the water.

See more: Who Wrote The Song Low Rider, Who Sang The Original Lowrider Song

A pair of nephridia is current within the mantle cavity. Sexual dimorphism is seen in this class of animals. Members of a species mate, then the female lays the eggs in a secluded and also protected niche. Females that some types care for the eggs because that an extended duration of time and may finish up dying during that time period. Reproduction in cephalopods is different from various other mollusks in the the egg hatches to create a youth adult there is no undergoing the trochophore and veliger larval stages.