There are many different organisms that
live in our world both on land and sea. Many young children do not realize
that there are many organisms that live in the sea. The sea has many areas
that organisms can live. A group that has many representatives is within the
Phylum Mollusca, which consists of snails, clams, octopus, squid, and abalone.
Mollusks are a diverse group that are have several subgroups including
gastropods, cephalopods, bivalves, scaphopods, polyplacophoras, and
monoplacophoras. Gastropods include over 35,000 species
that live in water or on land. They have one shell that spirals. Abalone which
has one shell with 7 holes is also considered a gastropod. They attach
themselves to a hard substance like a rock. The entire
animal lives inside and moves around with a large food. Bivalves have two
equal shells which are hinged by an elastic substance. Bivalves have a foot
for burrowing into the sand or mud. Cephalopods include squid, cuttlefish,
octopus and nautilus. Most can swim very well, but many do not have shells.
Nautiluses’ have a shell that has the geometry called a "whorl" or
a coil that wraps around itself. They have tentacles to help them swim around. Scaphopods are burrowing animals that are also called tusk or tooth shells.
Polyplacophoras include chitons and have 8 overlapping plates and a foot that
helps them attach to a rock. Monoplacophoras have a cap-like shell and were
thought extinct until some were dredged in 1952.
A graphical summary of the six subgroups mentioned
above can be found on the next page.
- Print out the graphical representation of the six
subgroups. Go over
the major groups. For each group say the name and have students
repeat. Describe each group with the information given
above. Point out that mollusk
are invertebrates (animals without a backbone). Make sure the students know
what a backbone is, by having them touch their own spine.
- Give each pair of students a bag full of
different shells. Students should group
the shells into similar shapes and then have them count the number of shells
in each group. Discuss why they sorted them into different groups. Talk about
sorting like organisms by shape, size, or color. Emphasize that sorting
by same shape is the correct way to find the different types of mollusk.
These shells belong to the Phylum Mollusca, which includes snails, clams, and many other shelled animals. Remind
students that not all shells are mollusks. The majority of shells in these
bags will be gastropods (or snails). They have a spiral symmetry.