mollusks

features of the mollusk

The Mollusks body is often divided into different parts ( Figure 1.2): On the beach, you can find a wide variety of mollusk shells. 1. A head with eyes or tentacles. 2. In most species, a muscular foot, which helps the mollusk move. Some mollusks use the foot for burrowing into the sand, and others use it for jet-propulsion. 3. A mantle, or fold of the outer skin lining the shell. The mantle often releases calcium carbonate, which creates an external shell, just like the ones you find on the beach. The shell is made of chitin, a tough, semitransparent substance. 4. A mass housing the organs. 5. A complete digestive tract that begins at the mouth and runs to the anus. 6. Most ocean mollusks have a gill or gills to absorb oxygen from the water. 7. Many species have a feeding structure, the radula, found only in mollusks. The radula can be thought of as a "tongue-like" structure. The radula is made mostly of chitin. Types of radulae range from structures used to scrape algae off of rocks to the beaks of squid and octopuses. This is the basic body plan of a mollusk. Note the mantle, gills, and radula. Keep in mind the basic body plan can differ slightly among the mollusks.

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what are mollusks

When you take a walk along a beach, what do you find there? Sand, the ocean, lots of sunlight. You may also find shells. The shells you find are most likely left by organisms in the phylum Mollusca. On the beach, you can find the shells of many different mollusks ( Figure 1.1), including clams, mussels, scallops, oysters, and snails. Mollusks are invertebrates that usually have a hard shell, a mantle, and a radula. Their glossy pearls, mother of pearl, and abalone shells are like pieces of jewelry. Some mollusks, such as squid and octopus, do not have shells.

evolution of mollusks

Mollusks are probably most closely related to organisms in the phylum Annelida, also known as segmented worms. This phylum includes the earthworm and leech. Scientists believe these two groups are related because, when they are in the early stage of development, they look very similar. Mollusks also share features of their organ systems with segmented worms. Unlike segmented worms, however, mollusks do not have body segmentation. The basic mollusk body shape is usually quite different as well.

instructional diagrams

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questions

pearls are produced by mollusks.

-->  a. true

b. false

mollusks are the only organisms to have a radula.

-->  a. true

b. false

the mollusk shell is formed by the

a) radula.

-->  b) mantle.

c) chitin.

d) gills.

the foot of a squid is probably used for

a) movement along a surface.

b) burrowing into the sand.

-->  c) jet-propulsion.

d) all of the above

what parts of the mollusk contain chitin?

a) the shell and mantle

-->  b) the shell and the radula

c) the radula and the mantle

d) the gills and the mantle cavity

the head region of a mollusk contains the

a) gills and mantle cavity.

b) the foot and tentacles.

-->  c) the tentacles and radula.

d) the stomach and the radula.

what type of worms are most closely related to mollusks?

a) flatworms

b) roundworms

-->  c) segmented worms

d) shelled worms

diagram questions

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