Life Cycle - Natural Environment (3B)

  • Discovering the food chain of gastropods.
  • Comparing herbivores and carnivores. 
  • carnivore
  • herbivore


Students sort snails into carnivores and herbivores. 


The marine environment has many different environments where organisms can live.  There are consumers as well as producers, including carnivores, omnivores, and herbivores.  

The marine environment has physical conditions that change like those in the terrestrial environment.  The conditions, however, are different and include water temperature, salinity, ocean currents, depth, and nutrient supply.  Plants can only live in the upper 200 meters of water, because light cannot penetrate any further.  The farther you go down in water depth, the more you will only find consumers.  The ocean environment is very complex.

The gastropods are a very large group within the Phylum  Mollusca.  The group includes the conches, periwinkles, limpets, garden snails, and slugs.  Most gastropods have shells, generally in the shape of a spiral with numerous turns. Virtually every type of feeding habit is exhibited by gastropods.  Larger bottom dwelling carnivore gastropods burrow into the sand to reach their prey including volutes, bonnets, helmets, olive shells, harp shells, and whelks.  Some species in these groups smother the victims with their feet.  Some may grip the bivalve with the foot, pulling, or wedging the two valves apart with the edge of the shell.  Some are adapted to drill holes in the shells.

The living gastropod has a distinct head with a mouth, eyes and tentacles.  Most have an organ in their mouth area called a radula, a series of rows of minute teeth on a flexible piece of flesh with which they scrape up food, tear the flesh of prey, or bore holes in the shells of clams.  Gastropods may be plant-eaters, carnivores, scavengers, deposit-feeders (obtaining food particles from sediment) or suspension-feeders (straining suspended food particles from the water.  It is very difficult to determine if a snail is a herbivore or carnivore by looking at its shell.  Gastropod shells display an infinite variety of colors, patterns, shapes and sculpturing.  There is one clue that works most of the time when trying to determine if a snail is a herbivore or carnivore, by looking at the siphonal notch area of the shell.

  1. Make students realize that the oceans are not one homogeneous mass of salt water.  The marine environments has many biomes and niches, just like the land environment.
  2. Go over the diagram of a snail with students because the slight modification of the siphonal notch will give students clues on how to determine if a snail is a herbivore or carnivore.  
    If the notch is indented it is usually a carnivore, if there is no indentation it is usually a herbivore.  Of course, there are exceptions, but that is where books like the Audubon Pocket Guide to Familiar Shells can help.  On the lab sheet, students will describe the shells using the model shell picture as a guide.  Instruct student to determine if their shells are from a herbivore or carnivore.

  1. In the lab, students will look at their packets and determine which marine snails are herbivores or carnivores.  Remember it is important to have the students carefully observe the characteristics, then to get the correct answer. 

    Babylonia formosae -  carnivore
    Murex endiva - carnivore
    Rapana tomisiana - carnivore
    Delphinula sp. - herbivore
    Turritella sp. - herbivore
    Sundial - herbivore
    Land snail - herbivore

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