Molluscs are soft-bodied animals, normally enclosed in a shell.
The shell is current in oysters, clams, snails and snails. In some, corresponding to squid, the shell is inside and in others, it’s absent, as within the octopus.
Shells are essential to guard the tender our bodies of molluscs and stop water loss.
Molluscs reside in marine or freshwater aquatic environments and in humid terrestrial environments.
The Molluscaphylum is the second largest in variety of species, roughly 50 thousand, behind solely arthropods.
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These animals have a physique divided into:head, foot and visceral mass. The sense organs are discovered within the head.
The foot is chargeable for motion and, in some animals, such because the octopus, may be changed by tentacles. The visceral mass is the place all of the organs are situated.
Meals and Digestive System
Mollusks have a whole digestive system, with a mouth and anus. Meals is transported via the digestive tract, the place it’s subjected to the motion of enzymes. Vitamins are absorbed and distributed all through the physique via the blood.
Cephalopods and gastropods have aradula, a kind of tongue with sharp enamel, used to scrape meals.
Respiration
As a result of molluscs are present in all kinds of environments, they’ve several types of respiration.
- Gill respiration is carried out by molluscs that reside in water, corresponding to octopuses, squid and oysters.
- Pulmonary respiration is current in molluscs that reside in terrestrial environments, corresponding to snails.
- Cutaneous respiration happens in slugs that additionally reside in terrestrial environments, underground and in bushes.
Circulatory System
The circulatory system distributes vitamins and oxygen to the digestive and respiratory methods. The excretory system removes metabolic waste and eliminates it.
The circulatory system is open, and the center is situated dorsally within the visceral mass. The contractions of the center ship blood out into the physique, which flows into the vessels after which via gaps between the tissues.
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Molluscs reproduce sexually , with inside or exterior fertilization. Most molluscs have separate sexes, except for bivalves, that are hermaphrodites.
In exterior fertilization, males launch sperm and females launch eggs immediately into the water, the place the 2 gametes meet.
Within the case of inside fertilization, sperm are launched inside the feminine’s physique.
See additionally:Animal Kingdom
Classification
Molluscs are animals that are available all kinds of styles and sizes. They’re divided into three essential lessons: gastropods, bivalves and cephalopods.
Gastropods
Gastropods are molluscs which have a spiral shell made up of a single piece. Examples of gastropods embrace snails, slugs and snails. They symbolize the most important group of molluscs.
Their visceral mass is contained in the shell, forming a single piece. They use their toes for locomotion.
Gastropods are terrestrial invertebrate animals .
Bivalves or Pelecypods
Bivalves are marine molluscs, fashioned by two articulated shells joined by a ligament. Examples of bivalves embrace clams, oysters and scallops.
Between the 2 shells is the animal’s physique, consisting of the foot and the visceral mass. The foot is small or absent.
Cephalopods
Cephalopods shouldn’t have a shell or the shell is inside. Examples of cephalopods embrace octopus, squid and nautilus.
They’re probably the most complicated molluscs, with a extremely developed nervous system and eyes much like these of vertebrates.
Tentacles prolong from the top, eight in quantity in octopuses and ten in quantity in squid. The tentacles have suckers that can be utilized to seize prey or connect the animal to a substrate, corresponding to a rock.
The octopus has an ink gland linked to its gut. When the animal is attacked, the gland expels ink, complicated the predator and making it simpler for the octopus to flee.
Cephalopods and bivalves are aquatic invertebrate animals .
Curiosities
- Within the Pacific Ocean, there are big shellfish, measuring greater than 1 meter in diameter and weighing round 300 kilos.
- Squids can attain 15 meters in size.
- Escargot, a kind of snail extremely valued as meals, is raised with particular care relating to meals, temperature and humidity.
- The manufacturing of pearls by oysters is of nice financial significance. The shells can be utilized to make buttons, combs and different objects.
- Annelids have some related traits to mollusks. Each have tender our bodies and reside in humid environments. Nevertheless, annelids shouldn’t have any sort of protecting shell.
Be taught extra about:
- Invertebrate Animals
- Animals: classification and traits
- Octopuses