Phylum Mollusca (Mollusks)
Mollusks are soft-bodied animals that usually have an internal or external shell. Mollusks include snails, slugs, clams, squids, and octopi.
Body Plan: The body plan of most mollusks has four parts: foot, mantle, shell, and visceral mass.
Respiration: Aquatic mollusks breathe using gills inside their mantle cavity. Land mollusks breathe using a mantle cavity that has a large surface area lined with blood vessels. Because they have to keep this lining moist, snails and slugs like in wet places.
Circulation: Slow moving mollusks have an open circulatory system, blood is pumped through the vessels by a simple heart. Faster moving mollusks have a closed circulatory system, can transport blood through much more quickly than an open circulatory system. Excretion: Tube-shaped nephridia removes ammonia from the blood and release it outside of the body. Response: Clams and shelled mollusks have a simple nervous system, small ganglia, few nerve cords, simple sense organs like chemical receptors and eyespots. Octopi have well developed brains that allow them to remember things and make them capable of complex behaviors like opening a jar to get food. Ecology of Mollusks: Mollusks clean up their surroundings by filtering algae out of the water. Can be used to measure water quality. Also for humans to eat! Octopus opening a jar! http://www.youtube.com/watch?v=5LYxJHi-RO0 |
Feeding: Mollusks can be herbivores, carnivores, filter feeders, detritivores, or parasites. Snails and slugs feed using a tongue-shaped structure called a radula. (Bellow) Herbivorous mollusks use their radula to scrape algae off rocks. Carnivorous mollusks use theirs to drill through shells of other animals
Reproduction: Many snails reproduce sexually by external fertilization. In tentacle mollusks, internal fertilization takes place inside the body of the female. Some mollusks are hermaphrodites, having both male and female reproductive organs.
Classes of Mollusks:
Gastropods: shell-less or single-shelled mollusks that move by using a muscular foot located on the ventral side. Bivalves: Have two shells that are held together by one or two powerful muscles. Cephalopods: Soft-bodies mollusks in which the head is attached to a single foot. The foot is divided into tentacles or arms. |