![]() ![]() The mantle: the layer of tissue that covers the visceral mass.Together with the foot, the visceral mass fulfills the function that is performed by the coelom in other protostomes. The visceral mass: the region that contains the internal organs and the external gill.The foot: a large muscle at the base of the animal, usually used for movement.The mollusk body plan is based on three main components: The mollusks are mainly marine animals and include the Bivalves (clams, muscles, scallops), Cephalopods (squid, octopus, cuttlefish, nautilus), the Chitons, and the Gastropods, of which some are terrestrial snails and slugs. Without the need for hydrostatic movement, the coelom is reduced to a cavity that transfers fluids and provides space for the internal organs. Rather than moving using a hydrostatic skeleton, arthropod muscles are directly attached to the exoskeleton. They have jointed limbs (hence the name from the Greek arthro- “joint”, and pod “foot”), and a tough exoskeleton made from chitin, often hardened with sclerotin proteins. They are the most numerous of all living creatures, making up over 80% of all described species. This group includes all insects, crustaceans, arachnids and myriapods. The main distinguishing feature of the arthropods is their segmented bodies, which are split into three distinct sections: the head, the thorax and the abdomen. To feed, Nemertea extend the proboscis outside the mouth and capture prey using venom and entangling. Nemertea (ribbon worms) have a proboscis with a barbed tip that lies inside the body just above the gut.Pripulida (penis worms) are marine worms that have a toothed throat that they turn inside out to extend, grab prey and then retract back into the body for consumption.They acquire food (and move) using a proboscis-a structure that extends in front of the mouth-which traps food particles in mucus and passes them through to the mouth with cilia. Echiura (spoon worms) are a small group of marine, segmented worms.The coelom acts as a hydrostatic skeleton, which uses fluid pressure to allow movement.Īlthough they have similar body plans, they are differentiated according to their specialized feeding systems. The majority of worm-like protostomes have a well-developed coelom, a cavity inside the body which provides space for fluids to circulate. This allows suspension (filter) feeding by pulling in water and food particles into the mouth and to the gut. Some have a ‘lophophore’: a specialized ring-like structure around their mouths. ![]() For example, mollusks grow larger by adding calcium carbonate to the edges of their shells.
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