what are the 4 main classes of mollusks

Classes of Molluscs

Classes of Molluscs For more than 50 years five classes of living molluscs were recognized: Amphineura, Gastropoda, Scaphopoda, Bivalvia (also called Pelecypoda), and Cephalopoda.

Full Answer

What are the three groups of mollusks?

• GASTROPODA (single shelled cowries, cones etc)
• BIVALVIA ( two shelled like clams, mussels etc)
• APLACOPHORA (solenogasters)
• MONOPLACOPHORA (segmented limpets)
• POLYPLACOPHORA ( or Amphineura as it was earlier called- Chitons)
• SCAPHOPODA (tusk shells)

What are the 3 major classes of phylum Mollusca?

• Gastropods. Gastropods include snails and slugs. They use their foot to crawl.
• Bivalves. Bivalves include clams, scallops, oysters, and mussels.
• Cephalopods. Cephalopods include the octopus and squid.

What are the main characteristics shared by all mollusks?

What are the main characteristics shared by all mollusks?

• They are bilaterally symmetrical.
• They are triploblastic, which three layers.
• They show organ system grade of organisation.
• The body is soft and unsegmented.
• Body is divisible into three regions – head, a visceral mass, and ventral foot.
• Body is covered by a mantle and shell.

What are the different types of mollusks?

list of mollusks

• class Aplacophora
• clams, mussels, oysters, and scallops (class Bivalvia)
• octopi, squid, cuttlefish, and nautili (class Cephalopoda)
• snails and slugs (class Gastropoda)
• class Monoplacophora
• class Polyplacophora
• class Scaphopoda
• extinct mollusks. This article was most recently revised and updated by Richard Pallardy. ...

What are the four main classes of mollusks?

ClassificationClassMajor organismsGastropodaall snails and slugs including abalone, limpets, conch, nudibranchs, sea hares, sea butterfliesBivalviaclams, oysters, scallops, geoducks, mussels, rudists†PolyplacophorachitonsCephalopodasquid, octopuses, cuttlefish, nautiluses, Spirula, belemnites†, ammonites†6 more rows

What are the major groups of mollusks?

The three major groups of mollusks are gastropods, bivalves, and cephalopods (SEF ul o pods). The largest group is the gastropods. These are mollusks like snails and slugs that have just one shell or no shell at all.

What are the 4 main characteristics of mollusks?

Mollusca CharacteristicsThey are mostly found in marine and freshwater. ... They exhibit organ system level of organization.Their body has a cavity.The body is divided into head, visceral mass, muscular foot and mantle.The head comprises of tentacles and compound eyes.The body is covered by a calcareous shell.More items...•

What are classes of mollusks?

Living mollusks are usually grouped into eight classes: Gastropoda (see gastropod), Bivalvia or Pelecypoda (see bivalve), Cephalopoda (see cephalopod), Scaphopoda (tusk shells), Aplacophora (Solenogasters), Caudofoveata (sometimes included in the Aplacophora order), Polyplacophora (chitons), and Monoplacophora.

How many mollusk types are there today?

Along with the insects and vertebrates, mollusks are one of the most diverse groups in the animal kingdom, with nearly 100,000 (possibly as many as 150,000) described species. This is a list of notable mollusks, ordered alphabetically by class. Also included are extinct mollusks.

How many classes of molluscs are there?

The Phylum Mollusca consist of 8 classes: 1) the Monoplacophora discovered in 1977; 2) the worm-like Aplacophora or solenogasters of the deep sea; 3) the also worm-like Caudofoveata; 4) the Polyplacophora, or chitons; 5) the Pelecypoda or bivalves; 6) the Gastropoda or snails; 7) the Scaphopoda, or tusk shells; and 8) ...

What are the 6 molluscs?

Class Gastropoda – snails, slugs, limpets, whelks, conchs, periwinkles, etc.

What are the characteristics of all mollusks?

WHAT FEATURES DO MOLLUSKS HAVE IN COMMON? As well as a shell, most mollusks have a muscular foot for creeping or burrowing. Some also have a head with sense organs. The soft body includes lungs or gills for breathing, and digestive and reproductive parts, all enclosed by a skinlike organ called the mantle.

What is a mollusk?

Mollusk definition. Mollusks are invertebrates whose integumentary system is soft like annelids. There are some which carry a protective shell, while others do not. Mollusks are the second largest group of invertebrate animals after arthropods. There are roughly 100,00 species of mollusks, of which 60,000 are gastropods.

Which class of fish has a shell?

This shell may be absent in some species. Class Cephalopoda: this class made up of octopuses, cuttlefish, squid and nautilus and, surprisingly, all carry a shell. The most obvious is that of the nautilus, whose shell is external. Sepias and squid have an internal shell which varies in size.

What class is Caudofoveata?

Class Caudofoveata: includes molluscs shaped like worms. They have no shell, but their body is covered with calcareous and aragonitic spicules. They live buried in the ground with their heads down.

How many tentacles does an octopus have?

Another important characteristic of cephalopods is that their muscular foot (present in molluscs) are tentacles. Cephalopods can carry between 8 to more than 90 tentacles, depending on the species.

Where do sea cockroaches live?

The sea cockroach is a kind of endemic Polyplacophora marine mollusk from Mexico. It lives on the rocky substrate in intertidal zones. It is a large species, able to reach 7.5 centimeters in length.

Which foot is ciliated, muscular and includes mucous glands?

Locomotor foot: is ciliated, muscular and include mucous glands. This ‘foot’ carries several pairs of dorsoventral muscles that serve to retract the foot and attach it to the mantle.

Do mollusks have radula?

Many solenogastres (mollusk subclass) lack radula. Additionally, bivalve, a class of marine and freshwater molluscs, have no radula. When it comes to a mollusk circulatory system, only the heart and the nearest organs have vessels. A mollusk heart is divided into two atria and a ventricle.

What are the different classes of molluscs?

Here is a commonly used classification for molluscs. Phylum Mollusca is classified into seven classes; GASTROPODA (single shelled cowries, cones etc) BIVALVIA ( two shelled like clams, mussels etc) APLACOPHORA (solenogasters) MONOPLACOPHORA (segmented limpets)

How many species are there in the phylum mollusca?

They are the second largest group of living organisms and are represented by a humongous number of species, more than a 100,000.

What is a gastropod called?

This word is a combination of two Greek words : ‘Gastir which means ‘stomach’ and podi which means ‘foot’. So Gastropods can be called ‘stomach-footed’ molluscs!! Funny isn’t it? Try acting out a gastropod!!! As the name suggests these have a well developed muscular foot, sometimes quite large that is used for crawling. There is a head with well developed eyes and tentacles. ( observe a land snail and you can see the tentacles coming out and going in). Except the slugs all gastropods produce an outer shell which is spirally wound. A kind of spiral coiling is seen as the animal grows. The immature organism is bilaterally symmetrical but acquires an asymmetrical shape as it matures into an adult. The coiling of the visceral mass around the central axis occurs through a process called torsion. This class with 17 orders and many families contain animals whose shell shape and structure also help to identify them. A Cone shell is easily distinguished from a top shell or a cowry. Refer to the illustration for parts of this shell. They live on land, freshwater and marine environment.

What is a mollusc without plates?

‘Without plates’ is what this term means. Aplacophorans are small, cylindrical, worm-like creatures that were till 1987 classified under Phylum Echinodermata as Holothurians. These benthic (deep water), exclusively marine molluscs do not have shells but have small calcareous spicules embedded in their mantle. There is no head or specialized excretory organ (nephridia). The foot and mantle cavity are reduced. Sea cucumber is the most familiar example of this class.

How many groups in sequence are there in biology?

In case you have problems remembering the 7 groups in sequence, then you could perhaps remember this sentence, that I remember reading in a biology text book during my school days:

What are the categories in classification?

In between these groups there are other categories such as Sub-class, Suborder, Superfamily & subfamily, Subgenus, and tribes, subspecies and varieties.

How many hierarchical categories are there?

But as a beginner it would suffice if you are able to remember the 7 hierarchical categories given above. The other minute details are important if and when you chose to study something scientifically.

What are the five classes of living molluscs?

For more than 50 years five classes of living molluscs were recognized: Amphineura, Gastropoda, Scaphopoda, Bivalvia (also called Pelecypoda), and Ce phalopoda. Discovery of Neopilina in the 1950s added another class (Monoplacophora), and Hyman* contended that

What is the largest class of molluscs?

Class Gastropoda. Among molluscs class Gastropoda is by far the largest and most diverse, containing about 40,000 living and 15,000 fossil species. It contains so much diversity that there is no single general term in our language that can apply to them as a whole.

How many pairs of gills does Neopilina have?

Neopilina has five pairs of gills, two pairs of auricles, six pairs of nephridia, one or two pairs of gonads, and a ladderlike nervous system with 10 pairs of pedal nerves. The mouth bears the characteristic radula. Class Polyplacophora: Chitons.

What are the two groups of solenogasters?

solenogasters and chitons make up separate classes (Polyplacophora and Aplacophora), lapsing the name Amphineura. Recognition of important differences between organisms such as Chaetoderma and other solenogasters has separated Aplacophora into the sister groups Caudofoveata and Solenogastres.†

What do snails eat?

Melongena feeds on clams, especially Tagelus, the razor clam, thrusting its proboscis between the gaping shell valves. Fasciolaria and Polinices (Figure 16-15B) feed on a variety of molluscs, preferably bivalves. Urosalpinx cinerea, oyster borers, drill holes through the shell of oysters. Their radula, bearing three longitudinal rows of teeth, is used first to begin the drilling action, then the snails glide forward, evert an accessory boring organ through a pore in the anterior sole of their foot, and hold it against the oyster’s shell, using a chemical agent to soften the shell. Short periods of rasping alternate with long periods of chemical activity until a neat round hole is completed. With its proboscis inserted through the hole, a snail may feed continuously for hours or days, using its radula to tear away the soft flesh. Urosalpinx is attracted to its prey at some distance by sensing some chemical, probably one released in metabolic wastes of the prey.

What is a tusk shell?

Scaphopoda, commonly called tusk shells or tooth shells, are benthic marine molluscs found from the subtidal zone to over 6000 m depth. They have a slender body covered with a mantle and a tubular shell open at both ends. In scaphopods the molluscan body plan has taken a new direction, with the mantle wrapped around the viscera and fused to form a tube. Most scaphopods are 2.5 to 5 cm long, although they range from 4 mm to 25 cm long. Dentalium (L. dentis, tooth) is a common Atlantic genus.

What are the members of the Caudofoveata?

They are mostly burrowers and orient themselves vertically , with the terminal mantle cavity and gills at the entrance of the burrow. They feed on microorganisms and detritus. They have no shell, but their bodies are covered with calcareous scales. There are no spicules or scales on the oral pedal shield, an organ apparently associated with food selection and intake. A radula is present, although reduced in some, and sexes are separate. This little group has fewer than 70 species; however, its features may be closer to those of the common ancestor of molluscs than any other living molluscs.

What is a mollusk?

Mollusk, any soft-bodied invertebrate of the phylum Mollusca, usually wholly or partly enclosed in a calcium carbonate shell secreted by a soft mantle covering the body. Along with the insects and vertebrates, it is one of the most diverse groups in the animal kingdom, with nearly 100,000…

What are the animals that are considered insects?

Worldwide in distribution, they include animals as diverse as sea stars, sea urchins, earthworms, sponges, jellyfish, lobsters, crabs, insects, spiders, snails,…. insect. Insect, (class Insecta or Hexapoda), any member of the largest class of the phylum Arthropoda, which is itself the largest of the animal phyla.

What is the most diverse group of animals?

mollusk . Mollusk, any soft-bodied invertebrate of the phylum Mollusca, usually wholly or partly enclosed in a calcium carbonate shell secreted by a soft mantle covering the body. Along with the insects and vertebrates, it is one of the most diverse groups in the animal kingdom, with nearly 100,000…. invertebrate.

What are the different classes of mollusca?

The following points highlight the six main classes of phylum mollusca. The classes are: 1. Monoplacophora 2. Amphineura 3. Gastropoda 4. Scaphopoda 5. Pelecypoda or Bivalvia or Lamellibranchiata 6. Cephalopoda.

What is an asymmetrical mollusc?

Asymmetrical molluscs with a spirally coiled mantle and a shell of one piece en­closing a corresponding visceral mass. The asymmetry of visceropallium is its funda­mental feature. 2. A well-developed head bearing eyes and tentacles are usually present.

What stages does a larva pass through?

9. The larva passes through trochophore and veliger stages.

How many suckers does a squid have?

4. The head bears eight non-retractile ten­tacles which are provided with suckers in two rows.

How many species of Nautilus are there?

Only one living genus with three species of Nautilus in eastern Pacific and Indian Oceans at depths to 560 metres; 2,500 fossil species. Example: Nautilus pompilius.

What subclass is Solenogastres?

Subclass i. Aplacophora or Solenogastres: 1. The body is elongated and worm-like and enveloped by the mantle. 2. The shell is absent and the body is covered with a cuticular mantle enclosing spicules of calcified material.

Which system is primitive, with longitudinal pallial and pedal cords with cross anastomoses?

2. The nervous system is primitive, with longitudinal pallial and pedal cords with cross anastomoses.

What is the difference between a squid's tentacles and its arms?

Examine the preserved Squid - The tentacles have suckers attached and are longer than the arms. Mouth has beak like jaws. Pigment cells allow the skin to darken from white to almost black. Identified the high developed nervous system with complex eyes and sensory organs.

What is the size of a snail?

Have a wide array of body plans and shell shapes as well as spiral shell with a variety of colors and different shaped mantles. range in size from .02 - over 30 inches

What class of molluscs are clams?

Joints between the plates allow the chiton to curl up in a ball and to move flexibly (Figs. 3.51 A and 3.53 A). The class of molluscs called Bivalvia (from Latin root words bi - meaning two and - valv meaning folding door) includes clams, oysters, mussels, and scallops.

What is the shell of a mollusc?

In most molluscs, the mantle produces a hard protective shell. The mantle also creates patterns of color on a shell. The shell is an exoskeleton, even though it is completely surrounded by soft tissue in some molluscs. The shell is continually produced and grows with the animal. Chitons are in the class Polyplacophora ( poly meaning many; placo meaning plate or shell; phora meaning bearing ). A chiton’s mantle produces eight shell-like plates that cover the body. Joints between the plates allow the chiton to curl up in a ball and to move flexibly (Figs. 3.51 A and 3.53 A). The class of molluscs called Bivalvia (from Latin root words bi - meaning two and - valv meaning folding door) includes clams, oysters, mussels, and scallops. Bivalves produce two shells that are hinged at the top (Fig. 3.49 B). The mantle of snails (gastropods) produces a single shell in a spiral shape (Fig. 3.49 C). The mantle itself cannot be seen because it is on the inner surface of the shell. In some gastropods, such as the cowries, the mantle extends over the shell, keeping the shell shiny and new in appearance. In other gastropods, like the sea hares, and in some cephalopods, like the squid and the octopus, the shell is very small and the mantle covers the shell completely (Fig. 3.49 D). The nudibranchs, or sea slugs ( nudi - meaning naked, - branch meaning gill ), are gastropods that don’t produce a shell, so these animals are all soft-bodied (Fig. 3.49 E). The chambered nautilus is one cephalopod that secretes an external shell. Squid and cuttlefish produce internal shells that are contained within the mantle, and octopus do not produce shells at all.

What is the radula of a snail?

The radula is a hard ribbon-shaped structure covered in rows of teeth. Herbivorous snails have a mouth with a radula of usually five to seven complex teeth. There is a great diversity of radula forms in the mollusca (Fig. 3.54). The snail uses its radula like a file, rasping it back and forth over the substrate to scrape off small bits of food (Fig. 3.55). As radular teeth wear down or break off, new teeth are formed to replace them. The tooth patterns of snail radulas are distinctive to species, and scientists can identify snails by looking at their radulas. Some radulas are highly specialized. A group of gastropods called cone snails are carnivorous (meat-eating) hunters that produce venom in glands near the mouth. Their radulas are shaped into long, hollow teeth, which they thrust one at a time into their prey like harpoons (Fig. 3.56). A barbed radular tooth fires through the proboscis, which is an extension of the mouth. It pierces the prey, paralyzing it with venom and preventing its escape. The cone snail “swallows” the prey by engulfing it with its proboscis. In this way cones stalk and capture worms, molluscs, and even fish. Some cones produce a poison strong enough to kill humans who handle them carelessly. Their poison is a neurotoxin that attacks and destroys nerves.

What are molluscs' gills called?

Molluscs breathe with gills called ctenidia that sit in a cavity between the mantle and body mass (Fig. 3.57). In some molluscs, most notably bivalves like oysters and mussels, the ctenidia are also used as filter feeding apparatus to strain particulate food from the water. Molluscs have a complete digestive tract surrounded by a small coelom. The molluscan circulatory system is composed of a series of blood sinuses or cavities, rather than closed, discrete vessels. This is referred to as an open circulatory system. Molluscs display a large diversity of nervous systems, from the rudimentary nervous system of the brainless bivalves to the complex systems of the cephalopods, who have well-developed brains and are considered the most intelligent of invertebrates.

What is the second largest animal phylum?

Image courtesy of Jan Delsing, Wikimedia Commons. The phylum Mollusca is the second-largest animal phylum, with over 100,000 species. The molluscs include many familiar animals, including clams, snails, slugs, and squid, as well as some less familiar animals, like tusk shells and chitons (Fig. 3.51 A).

What is the name of the sea slug's foot?

Because a sea slug’s stomach is in its foot, it is named Gastropoda, “stomach-foot” (from the Greek root words gastro meaning stomach and pod meaning foot; Fig. 3.53 B). The foot in octopus and squid is modified into many tentacles that are attached to the animal’s head (Fig. 3.53 D). That feature gave the class its name Cephalopoda (from the Greek root word cephal - meaning head ), or the “head-foot” molluscs. Octopus and squid use their tentacles for moving and for grasping and holding the prey they capture for food.

What is the purpose of a mollusc's foot?

3.53). Molluscs have a mantle or mass of soft flesh that covers the soft body and encloses the internal organs .