Squid Dissection Lab:
Domain Eukarya
Kingdom Animalia Phylum Mollusca Procedure:
Ecology of the Mollusks: Mollusks feed on plants, prey on animals, and “clean up” their surroundings by filtering algae out of water. They are also an important source of food for many organisms, including humans. A recent exploration in the deep sea discovered symbiotic bacteria within bivalves. The bacteria extract chemical energy that can produce food molecules that mollusks can use. Mollusks serve as important subjects in biological research. Current investigations base on the observation that snails and other types of mollusks never develop any form of cancer. If scientists find out what protects their cells from cancer, they will gain insights on how to fight human cancer.
Groups of Mollusks: Gastropods include pond snails, land slugs, sea butterflies, sea hares, limpets, and nudibranchs. Gastropods are either shell-less or single-shelled. They move by using a muscular foot located on the ventral side. Many animals can pull completely into their shells when threatened. Many snails are protected by a hard disc on the foot that forms a solid door at the mouth of their shell when they withdraw. Some slugs and nudibranchs have no shell. They protect themselves by spending daylight hours under rocks and logs. Sea hares squirt ink into the surrounding water, producing “smoke screen” that confuses predators. Some nudibranchs have chemicals in their bodies that taste bad or are poisonous. When bitten the predator becomes ill. Members of the class Bivalvia have two shells that are held together by one or two powerful muscles. Bivalves include clams, oysters, mussels, and scallops. Clams burrow in mud or sand. Mussels use sticky threads to attach themselves to rocks. Scallops can move around rapidly by flapping this shells when threatened. Currents created by cilia on the gills circulate water through the bodies of bivalves. Filter-feeding bivalves use mucus and cilia on their gills to trap food particles in the water. Other bivalves use long, muscular extensions of tissue that surround the mouth to collect food material deposited in sand or mud sediments. Cephalopods are the most active of the mollusks. Cephalopods include octopi, squids, cuttlefishes and nautiluses. Cephalopods are typically soft bodied mollusks in which the head is attached to a single foot. The foot is divided into tentacles or arms. They have at least eight tentacles that all have sucking disks that grab and hold prey. Nautiluses have many tentacles but lack suckers. Instead they have a mucus like covering. Most cephalopods have only small internal shells or no shells at all. Cephalopods also have numerous complex sense organs that help them detect and respond to external stimuli. They distinguish shapes by sight and by touch. |