In all adult molluscs the kidneys are of coelomic origin. The coelom in the molluscs consists of three regions : the pericardium, the coelomoducts which form the kidney, and the gonocoel.
Most mollusk have two organs that are unique to this phylum: a specialized feeding organ called a radula and a dorsal layer of tissue called a mantle. The excretory system of mollusks is made up of tubular organs called nephridia that filter waste from internal body fluids.
Mollusk species that are exclusively aquatic have gills for respiration, whereas some terrestrial species have lungs for respiration. Additionally, a tongue-like organ called a radula, which bears chitinous tooth-like ornamentation, is present in many species, and serves to shred or scrape food.
Proper balance of the internal environment (homeostasis) of a fish is in a great part maintained by the excretory system, especially the kidney. The kidney, gills, and skin play an important role in maintaining a fish's internal environment and checking the effects of osmosis.
Aquatic mollusks “breathe” under water with gills. Gills are thin filaments that absorb gases and exchange them between the blood and surrounding water. Mollusks have a circulatory system with one or two hearts that pump blood.
Molluscs occur in almost every habitat found on Earth, where they are often the most conspicuous organisms. While most are found in the marine environment, extending from the intertidal to the deepest oceans, several major gastropod clades live predominantly in freshwater or terrestrial habitats.
Marine bivalves reproduce by releasing prodigious numbers of eggs and sperm into the water, where external fertilization occurs. The fertilized eggs then float in the surface plankton. Within 48 hours after fertilization, the embryo develops into a minute, planktonic, trochophore larvae.
In earthworms, members of the phylum Annelida, the excretory system consists of structural units called nephridia (the singular is nephridium). Each nephridium contains a ciliated tunnel that leads to a long, coiled tubule, which leads to a bladderlike sac (a primitive bladder).
Crustaceans and arachnids possess paired excretory organs (maxillary, antennal, or coxal glands) that open at the bases of certain appendages. Myriapods, insects, and some arachnids, such as spiders and mites, possess another type of excretory organ, Malpighian tubules, which open into the intestine.
EXCRETORY SYSTEMExcretory organ of molluscs is called Organ of Bojanus or kidney. In Pila it is made of an anterior and a posterior renal chamber which extract wastes from the blood. The posterior renal chamber also collects wastes from the pericardial cavity through a renal duct.
Protozoans : Protozoans have no excretory organs. The metabolic waste products i.e. ammonia is passed out by diffusion through the cell membrane in surrounding water. They carry out the process of excretion with the help of contractile vacuoles. Sponges : Ammonia is the main excretory product in sponges.
Many invertebrates such as flatworms use a nephridium as their excretory organ. At the end of each blind tubule of the nephridium is a ciliated flame cell. As fluid passes down the tubule, solutes are reabsorbed and returned to the body fluids.
The principal excretory organs of insects are the Malpighian tubules, working in conjunction with the hind gut (p. 252). Other haemocoelic structures, such as the nephrocytes, fat-body and some cephalic glands, have also been regarded in the past as excretory organs.
The excretory system of mollusks is made up of tubular organs called nephridia that filter waste from internal body fluids. What remains in the tubes is concentrated waste that is then excreted out of the nephridia exit pores in the mantle cavity.
Exchange of gases also takes place through the tube feet. Echinoderms lack specialized excretory (waste disposal) organs and so nitrogenous waste, chiefly in the form of ammonia, diffuses out through the respiratory surfaces. The coelomic fluid contains the coelomocytes, or immune cells.
Mollusks can be segregated into seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. These classes are distinguished by, among other criteria, the presence and types of shells they possess.
Vertebrate predators of snails and slugs include shrews, mice, squirrels, and other small mammals; salamanders, toads and turtles, including the uncommon Blandings Turtle Emydoidea blandingii; and birds, especially ground-foragers such as thrushes, grouse, blackbirds, and wild turkey.
Mollusk reproduce asexually by being hermaphroditic where they are both male and female they also asexually reproduce by budding.
Anatomy. Gastropods and cephalopods have paired eyes on their heads (and sometimes tails), but many molluscs do not have clear head regions in which to locate the eyes. Consequently, many molluscs may have a multitude of eyes in more unlikely places, such as along the edge of their shell.
Molluscs, with the exception of the most highly developed cephalopods, have no brain in the strict sense of the word. Instead, the cell bodies (pericarya) of nerve cells are concentrated in nerve knots (ganglia) in important parts of the body. Mollusc nerve cells have no myelin sheath.
To be more specific, an octopus belongs to a unique class of mollusks known as cephalopods. This class includes other creatures such as squid. To put it in simpler terms, this why an octopus has no bones — no skeleton — it is an invertebrate. A fish has a backbone and a skeleton — it is a vertebrate.
The Class Gastropoda (in Phylum Mollusca) includes the groups pertaining to snails and slugs.
Mollusks eat a variety of organisms (see below). - Bivalves – A sub-group of mollusks that includes clams, mussels, scallops and oysters. Bivalves live on the ocean floor and feed on plankton (they are filter feeders). - Gastropods – A sub-group of mollusks, including snails, nudibranchs and abalone.
Bivalves don't have a head. They feed by filtering out food from the water in which they live. Tiny particles of food get caught in the gills and cilia near the gills move the particles into the mouth.
they have lungs or gills, that exchange carbon dioxide from the animal for oxygen in the air or water.
The body plan of a mollusk usually consists of a head region, a muscular foot, and a visceral mass of internal organs that is often contained within a dorsal shell. Each class possesses some variation on this basic plan. The organization of the gastropod body is very similar to the basic body plan of mollusks.
Mollusks are subdivided into seven classes with most species found in three of those classes: Gastropoda, Bivalvia, and Cephalopoda. Gastropods make up the largest class of mollusks, and they include both snails and slugs. The remaining classes (Polyplacophora, Aplacophora, and Monoplacophora) have fewer species.
Most mollusks move with a muscular structure called a foot. The feet of different kinds of mollusks are adapted for different uses, like crawling, digging, or catching prey. These are mollusks like snails and slugs that have just one shell or no shell at all. Gastropods creep along on their broad foot.
Medical Definition of Mollusca: a large phylum of invertebrate animals (as snails, clams, and mussels) that have a soft unsegmented body lacking segmented appendages and commonly protected by a calcareous shell.
All mollusks have: a visceral mass containing internal organs, including the digestive tract, paired kidneys, and reproductive organs. a mantle that surrounds but does not cover entirely the visceral mass and secretes a shell (if one is present). The mantle also contributes to formation of gills or lungs.
The radula (/ˈrædj?l?/; plural radulae or radulas) is an anatomical structure used by mollusks for feeding, sometimes compared to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the oesophagus.
