The molluscs are a large group of invertebrate animals, almost as numerous as the arthropod animals. Although they are very diverse animals, we can find certain characteristics that make us classify them in this way. Do you want to know more about them?
In this article on our site we will learn about the types of molluscs that exist, their characteristics, classification and a list of molluscs to get to know slightly its diversity. Keep reading.
What are mollusks?
Molluscs are invertebrates whose integument is soft like annelids, but their body in the adult stage is not segmented, although some may be protected by a shell. It is the largest group of invertebrate animals after the arthropods. There are about 100,000 species, of which 60,000 are gastropods. In addition, 30,000 fossil species are known.
Most of these animals are marine benthic molluscs, that is, they live on the seabed. Many others are terrestrial, like some snails. The great diversity that exists means that these animals have colonized a multitude of different habitats and, therefore, all dietary regimens are present within the molluscs.
Also discover on our site the types of snails that exist, marine and terrestrial.
Characteristics of molluscs
Molluscs are a very diverse group and finding characteristics common to all of them is an arduous task. Therefore, we present the most common features, although there are many exceptions:
Your body is divided into four main zones:
- Mantle: It is the dorsal surface of the body that can secrete protection. This protection has a chitinous and protein origin that subsequently creates calcareous deposits, spicules or the shell. Some animals that do not have shells have chemical defenses.
- Locomotor foot: It is ciliated, muscular and with mucous glands. From it arise several pairs of dorsoventral muscles that serve to retract the foot and join it to the mantle.
- Cephalic zone: in this zone we find the brain, the mouth and other sensory organs.
- Pallial cavity: this is where the osphradia (olfactory organs), body openings (anus) and gills, called ctenidia, are located.
The digestive system of molluscs has some characteristic features:
- Stomach: they have extracellular digestion. The digestible particles are selected by the digestive gland (hepatopancreas) and the rest passes to the intestine to produce feces.
- Radula: this organ located inside the mouth is a toothed ribbon-shaped membrane, supported by the odontophore (mass of cartilaginous consistency) and moved by complex muscles. The appearance and movement are similar to that of a tongue. The chitinous teeth on the radula tear the food. Old and worn teeth fall out and new ones form in the radular sac. Many solenogastros lack a radula and no bivalves have one.
But in addition, the circulatory system is open, only the heart and the closest organs have vessels. The heart is divided into two atria and one ventricle. They do not have an excretory apparatus as such. They have metanephridia that collaborate with the heart, which is an ultrafilter, produces primary urine which will be reabsorbed by the nephridia, which also regulate the amount of water. The reproductive system has a pair of gonads in front of the pericardium. The gametes are evacuated to the pallial cavity, most of them attached to the nephridia. They can be dioecious or hermaphrodite.
Classification of molluscs
The mollusk phylum is divided into eight classes, all of which have living species. The classes of molluscs are:
- Class Caudofoveata: they are worm-shaped molluscs. They do not have a shell, but their body is covered with calcareous and aragonitic spicules. They live buried in the ground with their heads down.
- Class Solenogastrea: they are animals very similar to the previous class, so much so that historically they were included in the same group. They also have the shape of a worm, but instead of living buried they do so free in the ocean, feeding on cnidarians. Likewise, they present calcareous and aragonitic spicules.
- Class Monoplacophora: these are very primitive molluscs. Their body is covered by a single shell, like half a clam, but they have a muscular foot like a snail.
- Class Polyplacophora: At first glance they are similar to a type of crustacean, the sow bug. His body is covered by a set of magnetite-reinforced plates. They also have a crawling muscular foot and a radula.
- Class Scaphopoda: these molluscs have a very elongated body, as well as their shell, which is shaped like a horn, so they they are known as tusk shells. It is one of the best known types of marine molluscs.
- Class Bivalvia: Bivalves, as their name suggests, are molluscs whose body is enclosed between two valves or shells These two valves close thanks to the action of muscles and ligaments. The best known types of bivalve molluscs are clams, mussels or oysters.
- Class Gastropoda: gastropods are known snails and slugs, both terrestrial and marine. They have a well-differentiated head area, a muscular foot that is used for crawling or swimming, and a shell on the back. This shell may be absent in some species.
- Class Cephalopoda: the group of cephalopods is made up of the octopus, cuttlefish, squid and nautilusDespite what it may seem, they all have a shell. The most obvious is that of the nautiluses, as it is external. Cuttlefish and squid have a more or less large shell inside. The octopus shell is almost vestigial, it only has two fine calcareous strands inside its body. Another important feature of cephalopods is that the muscular foot present in molluscs has been transformed into tentacles. They can have from 8 to more than 90 tentacles, depending on the species.
Examples of molluscs
Now you know the characteristics and classification of molluscs. Next, we will look at some of the types of molluscs and examples:
1. Chaetoderma elegans
Shaped like a worm and without a shell, this type of mollusk belongs to the Caudofoveata class. It has a tropical distribution in the Pacific Ocean. It can be found at depths from 50 meters to more than 1800 meters.
two. Neomenian Carinata
It's another vermiform mollusk, but this time it belongs to the Solenogastrea family. It has been found in a depth range of between 10 and 565 meters living freely in the Atlantic Ocean, off the coast of Portugal.
3. Sea cockroach (Chiton articulatus)
The sea cockroach is a species of polyplacophorous mollusk endemic to Mexico. It lives on the rocky substrate in intertidal zones. It is a large species, and can reach 7.5 centimeters in length.
4. Antalis vulgaris
It is a kind of scaphopod mollusk with a tubular or fang-shaped shell. It is white. It lives in shallow sandy and muddy substrates, in intertidal zones. They can be found along the Atlantic and Mediterranean coasts.
5. Coquina or tellina (Donax trunculus)
Coquinas are small bivalves that usually live on the Atlantic and Mediterranean coasts. They are highly valued in the local culinary culture. They can live in the infratidal zone about 20 meters deep.
6. European flat oyster (Ostrea edulis)
Oysters are one of the bivalvetypes of molluscs in the order Ostreoida. This species can measure up to 11 centimeters and produces pearls made of mother-of-pearl They are distributed from Norway to Morocco and the Mediterranean. In addition, they are cultivated in aquaculture.
7. Common garden snail (Helix aspersa)
The common snail is a species of gastropod mollusk with pulmonary respiration, that is, they do not have gills and live on the surface of the earth. They need a lot of moisture, and when they don't have it, they hide inside their shell for long periods of time to avoid drying out.
8. Common octopus or rock octopus (Octopus vulgaris)
The common octopus is a cephalopod that lives in the Atlantic Ocean and the Mediterranean Sea. They are about a meter long and can change color thanks to the chromatophores. They have high value for gastronomy.
More mollusk names
Have you been wanting more? Below we will mention other species of molluscs:
- Scutopus robustus
- Scutopus ventrolineatus
- Laevipilina cachuchensis
- Laevipilina rolani
- Tonicella lineata
- Diffuse chiton or phantom chiton (Acanthopleura granulata)
- Ditrupa arietina
- Freshwater pearl oyster (Margaritifera margaritifera)
- Cocktail Mussel (Cristaria plicata)
- Sea snail (Iberus gu altieranus alonensis)
- veneer (Iberus gu altieranus gu altieranus)
- Giant African Snail (Achatina fulica)
- Common cuttlefish (Sepia officinalis)
- Atlantic giant squid (Architeuthis dux)
- Giant octopus or North Pacific octopus (Enteroctopus dofleini)
- Palaean Nautilus (Nautilus belauensis)
Discover also on our site how mollusks reproduce in a complete guide.
