Life Cycle - Organisms (KB)

  • Comparing different shells.
  • Investigating different shells.
  • invertebrate
  • organism
  • shell

Students sort and compare shells.





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. 

  1. 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.
  2. 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.

  [Back to Life Cycle Grid]  [Back to Organisms (K)]