Examples of mollusks embrace bivalves similar to clams, oysters and scallops; gastropods similar to slugs, snails, limpets, nudibranchs and sea hares; and cephalopods similar to squid, cuttlefish, nautiluses and octopuses.
Much less well-known examples of mollusks embrace chitons (class Polyplacophora), tusk shells (class Scaphopoda) and members of the courses Monoplacophora and Aplacophora.
(Observe: outdoors of North America, “mollusk” is spelt “mollusc”.)
Proceed studying to view the several types of mollusks and to search out out extra about mollusks usually, or use the index beneath to go on to the data you want.
Web page Index
What Is A Mollusk?
Mollusks are a big and various group of animals that make up the phylum Mollusca. Mollusks vary from small, worm-like animals that inhabit the mud of the ocean mattress, to cephalopods similar to cuttlefish and octopuses, that are among the many most clever of all animals.
(A phylum is a gaggle of associated animals that itself could be cut up into smaller teams similar to courses, orders and households. See this web page: Animal Classification for extra particulars.)
How Many Mollusk Species Are There?
There are 85,300 identified residing species of mollusks. (supply – The Catalogue of Life)
The place Do Mollusks Reside?
Most mollusks dwell within the sea, however some dwell in freshwater, and others, together with many species of slugs and snails, dwell on land.
When Did Mollusks First Seem?
Mollusks first appeared over 520 million years in the past, throughout the Cambrian Interval. Over time, mollusks have advanced to fill many ecological niches, even leaving their ancestral ocean residence and residing in freshwater and terrestrial habitats.
Though a bivalve similar to a mussel seems very completely different to a cephalopod similar to an octopus, each they, and all different residing mollusks, are descended from the identical, historic ancestors.
Mollusks are invertebrate animals with a nervous system and a physique half known as a mantle.
The mantle is a muscular wall that encloses the mollusk’s inner physique components and folds over to create the mantle cavity, which homes the mollusk’s gills (if current), along with its waste and reproductive openings. In mollusks that lack gills, the mantle cavity types a lung.
The shells of shelled mollusks are shaped by secretions from the mantle. Cephalopods can propel themselves by the water by speedy contractions of the mantle – a type of “jet propulsion”!
Most mollusks have a specialised mouth half known as a radula. The radula is coated with enamel and used to scrape meals from surfaces.
Bivalves lack a radula and as a substitute seize meals by filtering it from the water with specially-modified gills.
On the base of the our bodies of many sorts of mollusks is a muscular foot. In cephalopods, the meals is modified to type tentacles or arms.
Examples Of Mollusks
- Class: Bivalvia
- No. of species: 9,785 (supply)
A bivalve is a mollusk with a flat physique protected by two shells often known as valves. (The phrase “bivalve” means (“two valves”.) The valves are hinged alongside the again edge, and are closed by adductor muscle tissues. Bivalves are able to holding their shells shut with stunning power.
Bivalves lack heads and brains; their actions being managed by a comparatively easy (in comparison with these of different mollusks) nervous system.
Most bivalves are burrowers, however some can swim by quickly opening and shutting their valves, and others are sedentary, attaching themselves to underwater surfaces, and solely able to shifting of their larval type.
Bivalves are filter feeders, acquiring meals from the water with specially-modified gills. Bivalves lack a radula (the toothed, tongue-like organ present in different mollusks).
The title “mussel” has been given to a number of sorts of marine and freshwater bivalves, however is usually used to consult with bivalves of household Mytilidae, that are present in marine habitats.
Mussels are sometimes black or darkish blue in shade. They connect themselves to underwater surfaces, typically forming “beds” consisting of huge portions of mussels.
A number of mussel species are edible, and edible are harvested for meals in lots of components of the world.
There are a number of several types of oysters, together with the “true” oysters belonging to the household Ostreidae.
Some oysters are edible, and species such because the Pacific oyster are farmed for this function.
Though many sorts of mollusks can produce pearls, these most closely-associated with pearl manufacturing are pearl oysters. These oysters, which make up the genus Pinctata, are harvested particularly for the aim.
Not like most bivalves, many scallops are in a position to transfer, doing so by quickly opening and shutting their shells. Scallops are solely present in marine habitats, and are current in the entire world’s oceans.
Clams are edible bivalves that dwell partially buried in mud or sand on the backside of each marine and freshwater habitats.
The large clam is the largest residing bivalve, with a shell width of nicely over 1m / 3.28 ft. It at present has the conservation standing “Weak”, and is threatened by over-harvesting for meals. The large clam belongs to the genus Tridacna (the opposite members of this group are often known as “large clams”).
- Class: Gastropoda
- No. of species: 72,551 (supply)
Gastropods are a gaggle of mollusks generally often known as slugs or snails. This massive group consists of over 70,000 identified species and makes up round 80% of all mollusks. Gastropods are present in marine, freshwater and terrestrial (land) habitats.
Gastropods with shells are sometimes often known as “snails”; people who lack shells are often known as “slugs”.
All slugs (and snails) are mollusks. Banana slugs are significantly putting as a result of their giant dimension and vivid yellow shade. Banana slugs are a gaggle of gastropods (the genus Ariolimax) present in North America.
Large African Land Snail
The large African land snail (Lissachatina fulica) is the world’s largest residing land snail, reaching lengths of round 20 cm / 7.87 in. Initially native to East Africa, the species is right now discovered in lots of different components of the world because of human introduction. The snail is stored as a pet, and in addition used as meals.
Abalone are marine gastropods belonging to the household Haliotidae. The shells of abalone sometimes have a row of three or 4 respiratory holes.
Abalone are present in coastal waters of each ocean, and are most considerable in colder waters. Abalones are collected for meals and in addition for jewellery, the insides of their shells being extremely iridescent.
Whelks are sea snails with spiraled shells. They’re harvested for meals in lots of components of the world.
Though a number of gastropods are often known as whelks, “true whelks”, such because the frequent whelk (Buccinum undatum) belong to the household Buccinidae.
The title limpet is given to a number of several types of unrelated gastropods with conical, uncoiled shells.
Limpets are identified for his or her capability to connect themselves extraordinarily strongly to rocks and different surfaces. Not like mussels, limpets usually are not completely connected to the rock floor, and are in a position to transfer round.
Nudibranchs are a gaggle of sea slugs identified for his or her vivid colours. They’re present in oceans worldwide.
As larvae, nudibranchs have a shell, however that is shed when the animals metamorphosize into their grownup type.
Sea hares are marine mollusks whose rounded form and ear-like sensory projections give them a hare-like look.
- Class: Cephalopoda
- No. of species: 841 (supply)
The category Cephalopoda – the cephalopods – incorporates each the most important residing mollusk (the colossal squid), and essentially the most clever mollusks – cuttlefish, octopuses and squid are thought of to be the world’s most clever invertebrates.
The category Cephalopoda is split into two foremost teams: Coleoidea and Nautiloidea.
The subclass Coleoidea is residence to squid, cuttlefish and octopuses. These mollusks are characterised by the dearth of a shell, excessive intelligence, wonderful imaginative and prescient, the flexibility to squirt ink and alter shade, and using jet propulsion for motion.
The subclass Nautiloidea is residence to nautiluses. Right now, this group incorporates only a handful of species, all of which have distinctive, coiled shells and tentacle-like projections often known as cirri.
Cuttlefish are cephalopods with lengthy our bodies, eight legs and two tentacles. They propel themselves by the water with fins, and in addition by ejecting water forcibly from the mantle cavity. Their eyes have distinctive, W-shaped pupils.
A cuttlefish’s physique incorporates a tough, porous construction known as a cuttlebone. That is used to regulate the animal’s buoyancy.
The 300-or-so species of octopus make up the order Octopoda. Octopuses are marine mollusks with gentle our bodies and eight legs.
Like cuttlefish, squid have eight legs and two tentacles. Not like cuttlefish, squid lack a cuttlebone. As an alternative, their our bodies include a tough, feather-shaped formed construction known as a pen.
Squid are predatory animals, looking their prey by sight and utilizing jet propulsion to journey at excessive velocity by the water. Their prey consists of fish, crustaceans and different cephalopods, together with different squid (typically of the identical species).
Nautiloids are cephalopods with distinctive coiled shells, and are the one residing cephalopods with exterior shells. They transfer by jet propulsion and prey on crustaceans. Their eyes are much less well-developed than these of different cephalopods, they usually discover meals by sensing chemical substances within the water.
The six residing species on this group are divided between two genera: Nautilus, which incorporates 4 species, and Allonautilus, which incorporates the remaining two species.
Nautilus species are present in shallow, tropical waters, whereas Allonautilus species are although to inhabit deeper waters.
The chambered nautilus is the best-known nautiloid. It’s discovered within the South Pacific.
- Class: Polyplacophora
- No. of species: 1,063 (supply)
Chitons are marine mollusks within the class Polyplacophora. Not like bivalves and gastropods, chitons are solely present in saltwater. Chitons are present in oceans worldwide.
The shell of a chiton is split into eight separate components, often known as valves. This permits the chiton a level of flexibility when it’s shifting over rocks and different uneven surfaces. A chiton’s shell is surrounded or fully enclosed by a muscular construction often known as a girdle.
Most chitons are herbivores, feeding on algae, however some species are omnivorous and even carnivorous, capturing crustaceans and different animals below the girdle.
The black Katy chiton (Katharina tunicata) is discovered within the Pacific Ocean. It grows to round 12 cm / 4.72 in. in size.
- Class: Scaphopoda
- No. of species: 579 (supply)
Tusk shells (often known as tooth shells) are mollusks within the class Scaphopoda. Tusk shells dwell buried within the mud of the ocean mattress, and are present in oceans worldwide.
These lengthy, skinny shelled mollusks can attain lengths of as much as 18 cm / 7.09 in.
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- Class: Monoplacophora
- No. of species: 30 (supply)
Members of the mollusk class Monoplacophora are limpet-like, single-shelled animals that inhabit deep sea habitats.
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- Class: Aplacophora
- No. of species: c. 320
Mollusks of sophistication Aplacophora are small, worm-like animals discovered on the ocean mattress in oceans worldwide. Aplacophorans lack shells and exhibit a variety of life: some burrow within the sediment, whereas others dwell on the floor of the ocean mattress; some prey on small ocean animals, whereas others feed on detritus.
Some zoologists divide the category Aplacophora into two separate courses: Caudofoveata and Solenogastres.
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