Pope Sheldon (with Allison, Lam and Eric) Bio 412 Lab Section 18 4-3-08 Mollusca, Annelida, & Arthropoda Introduction: Mollusks are shelled creatures which have the ability to adapt to land and aquatic environments. Due to these abilities there is a great diversity in the mollusk family. A mollusk has protostomes with a reduced version of the true coelom. Mollusks have a basic body plan with an open circulatory system. The rest of their body includes visceral mass, a foot, and the mantle which usually secretes the animal's shell. Annelids which are segmented worms get their name from the latin word annel which means a ring. The true coelom found inside a segmented worm is lined with mesoderm, which is a type of skin layer. The protostomes is the main feature of these organisms. Metamerism is the reason for the name of these worms, it means serial segmentation. Segmented worms have a hydrostatic skeleton and longitudinal muscles, both of these features help them move and squeeze through tight places. A normal skeleton would not work for worms, but a closed circulatory system does, which is why segmented worms have one. Arthropod means jointed leg, which is what many simple animals and insects have. The organisms within this phylum all have jointed appendages. They also have protostomes with a true coelom, just like the mollusks. The exoskeleton of arthropods is made of chitin and protein or calcium carbonate. The arthropods have segmented bodies, not like the worm however, but they are separated into different parts. There is metamarism like segemented worms in arthropods. The only way for arthropods to grow is by shedding their exoskeleton; this allows them to "upgrade" their size.
There are several subphylums of arthropods; these are Chelicerata, Crustacea, and Atelocerata. The subphyla Chelicerata contain animals such as horseshoe crabs, and Sea Spiders. Crustacea contains popular creatures such as lobster, crabs, and shrimp. Atelocerata contains centipedes, millipedes and many other insects. Materials & Methods: The first thing we did was dissect a squid and quahog. squid The was dissected by just cutting up through the top of its body and the quahog was heated in a microwave to open the shell a little bit which then could be pried open enough to cut the adductor muscles. These were then drawn. Next I drew all of the following; an organism from class polyplacophora, one from bivalva, a leech from class Hirvdinea, and earthworm from Oligochaeta, a clam worm from Polychaeta, a crab from Crustacea, a grasshopper, butterfly, and roach from phyla arthropoda. The final drawing was a tarantula from phyla arthropoda, and class Arachnida. Results: See attached sheets for drawings. Discussion/Conclusion: Clams have an ingenious body design, yet it is also simple. There is an outer shell which is usually all you see, there are two shells held together by two adductor muscles inside the shell. There is a mantle which is like the outer skin of the innards. The mantle produces the shell and has a mouth and anus. On the inside of the mantle is the pseudopod or foot. This is how a clam moves. There is a siphon which takes water in and exhales water. This siphon extends beyond the mantle usually outside of the shell. A clam also has the normal organs that most
complex organisms have such as intestines, kidneys, gonads, and a stomach. The hinge ligaments are what hold the shells together. Cephalopods have very similar body structure to clams if you are not actually looking at them. The basic structures are the head, foot and mantle. The mantle in a cephalopod is what actually holds their organs. In mollusks, the shell actually protects the inner organs, but in a cephalopod, the mantle does that job. Unlike a mollusk the cephalopod has a brain and sense organs all together in its head. The foot of a cephalopod is attached to its head which is where it gets its name. Cephalopod is literally translated "head footed". This lab was pretty fun, we got to dissect a couple of cool creatures and see what was actually inside of them. This is terribly represented in my pictures due to a lack of artistic ability. Other than artistic ability there were no problems.