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The Why of Shells
Classroom activities prepare students for a beach field trip to observe shells in action and other structures and functions of the external parts of marine animals. Students will observe external structures of intertidal animals and identify important similarities in structures and their functions, including those that allow them to be placed into major groups (mollusks, crustaceans, echinoderms) in the classroom and on the field trip. They will sort and investigate different types of shells and different functions of shells. Student learning is assessed by the development of models that demonstrate understanding about how external structures solve problems related to survival and growth of organisms.
Essential Question(s)
What similarities and differences in external animal structures can be used to separate them into different groups?
How do the external parts of animals function to survive, grown, and meet their needs?
PDF Investigation
Time Required
Approximately 2-4 weeks
Life Sciences
Investigation Type
Field Trip, Classroom
Grade Level
NGSS Performance Expectations
Materials Needed

Pictures of different types of mollusks or crustaceans with shells in books in your school library or downloaded from the Internet, line drawings of marine invertebrates, and/or Bivalves of Alaska poster (can be ordered from the Alaska Sea Grant bookstore)

A collection of different types of mollusk shells (If these are not available, the pictures can be used again.)

3” X 5” or 6” X 8” index cards for the riddle game

Field Trip supplies: Laminated field guides for your local area, cameras, quadrat squares, buckets, magnifying boxes

NGSS Performance Expectation

Students who demonstrate understanding can:

Use materials to design a solution to a human problem by mimicking how plants and/or animals use their external parts to help them survive, grow, and meet their needs. 1-LS1-1

Develop a simple sketch, drawing, or physical model to illustrate how the shape of an object helps it function as needed to solve a given problem. K-2-ETS1-2


Knowledge - Students will know that:
  • all animals have external parts.
  • different animals use their body parts in different ways to fulfill specific functions related to survival.
  • the functions of different shell structures as body parts.
Skills - Students will be able to:
  • use materials to design a device that solves a specific problem or a solution to a specific problem.
  • group different types of marine animals into mollusks, echinoderms, and crustaceans based on similar external structures with similar functions
Local and Cultural Connections
Different types of clams, crabs, and shrimp are harvested for subsistence, recreational, and commercial purposes by Alaskans. Mussels are also harvested and chitons and snails are traditional Alaska Native foods. Shells have also been used traditionally in Alaska Native cultures for decoration and as a form of currency or symbols of wealth. In Tlingit culture, they are used as buttons on button blankets, as inlays in carvings and bentwood boxes, and as attachments to many objects as charms or rattles. Abalone buttons were especially prized traditionally.
Teacher Preparation

Teacher Preparation for Classroom activities:
Part 1 and 2. Gather books and pictures
Part 3. Gather and set out a collection of different types of mollusk shells that include bivalves and univalves. Include chiton shells, if possible. 
Collect recyclables for invent-a-shell project

Field Trip Preparation:
Schedule the field trip for the lowest possible tide and distribute/ collect permission forms.
Make quadrat squares (See directions to make one out of PVC pipe).
Develop a format for field trip observation notes.
Assign students to chaperone leader groups.

Obtain labels, or sticks, to give to chaperones for placement in pictures of quadrat squares.

Learning Experiences

Part 1: (Classroom) Observe Animal Structures

(4 or 5 class periods)


(15-20 mins.)

  1. Use books, written material and/or video clips to give students the opportunity to observe characteristics and features of a variety of the animals they are likely to see on their beach field trip.

  2. Discuss differences in similar structures (numbers and shape of arms and legs, noses, ears, eyes, or the lack of any obvious structure of this type on some animals; hard and soft structures, etc.).

  3. Write the names of structures you point out or students observe on the board. After you have made the list, discuss the how the animal uses each structure in terms of a function necessary for the survival of all animals. Ask: Can some types of structures on the same animal have different functions? (Example: A crab’s front pair of legs end in pincers that function to grasp and tear up food to place it the mouth, to break open mollusk shells, and to fight with other crabs. The other eight pairs of legs function in side-ways locomotion.) Be sure to include body parts (octopus eyes, structures at the tips of sea star arms sensitive to light and dark, the tips of snail tentacles) that function to capture and convey different kinds of information needed for growth and survival.


(30 mins.)

What Do You Know?

  1. Compile a class list of tide pool or beach animals that students know and predict they might see on their beach field. Use common group names. (Examples: limpets, snails, clams) Encourage the use of common names for individual species based on physical characteristics such as the wide-handed crab, blue mussel, etc.

  2. Assign each student to draw a different animal to put together in a field guide. Discuss how to group the animals together based on external structures.

Optional: You can use the characteristics to “translate” scientific names of the groups by calling attention to their soft bodies and large, single foot in different locations in their overall structure.
Mollusk translates as “soft.”

The mollusk group for snails, gastropods, translates as “stomach foot.”

The mollusk group for octopus and squids, cephalopods, translates as “head foot.”

Echinoderm translates as “spiny-skinned.”Crustaceans: “crusta” translates as “hard-shelled.”

Arthropoda (insects, spiders, and crustaceans) as “jointed legs.”


(30 mins./day, 3 days)

  1. Help students group the drawings into spiny-skinned, jointed legs, and soft-bodied with shells OR echinoderms, crustaceans, and mollusks and “others.” Make a large class chart with the title: “Meet the Invertebrates.” Write the group names at the head of columns and rows for “How They Move,” “How They Get Food,” “How They Avoid Being Eaten” and “How They Use Their Senses.” Introduce the invertebrate groups and describe each group’s unique characteristics as a class as you fill in the chart.

  2. Introduce vocabulary for two different types of shell structures for mollusks: “bivalve” for a two-shelled structure, “univalve” for a one-shelled structure. Use books (See Resources section), other written material and video clips of mollusks to show different characteristics and features of different types of shells, including the eight shell plates of chitons.

  3. The WHY? of Shells.

    Ask: What are they made of and what is their function?

  4. Brainstorm all the possible uses of a shell by a mollusk:

    How are they used as armor?
    As a way to stay wet when the tide is out?
    As portable homes?
    By animals who aren’t mollusks
    ? (Hermit crabs, barnacles and limpets that settle on them and use them for “free” transportation) How do people use shells? (Jewelry, a traditional form of money, art, ”button” blankets, decoration, containers.)

  5. Discuss the possible uses and advantages or disadvantages of a different number of shells (1 for univalves, 2 for bivalves, 8 for chitons) for specific functions such as defense, staying wet when the tide is out, etc.


(20-30 mins.)
Have students sort a collection of different types of mollusk shells into univalves and bivalves. As a whole-class game or at partner centers, use pictures, shells, and/or stuffed animals or puppets with teacher-created riddle cards to reinforce connections between external structures and function to animal groups. Example: “I have a large foot to move around on slowly.” “I have two shells that I clamp together tightly to stay wet and defend myself from being eaten by gulls.” Make up your own riddle cards or use the ASW What Do You Know? Cards. This activity could be a game played by the whole class, or partner center.

Art Project Extensions:

Jellies and Hermit Crabs:

Students may share their sea creature models in the library or hallway mural.

Part 2: Beach Field Trip

(1 ½ - 2 hours)

Preparation for Field Trip:

Review tide pool etiquette rules.

Have students practice using a quadrat sampler to sample an area of the floor or playground. To give them experience observing structures and inferring functions, you can spread out a collection of small toys or classroom items (paper clips, markers, glue sticks, etc.) and have them count and describe items in different layouts within the sampled area.

At the Beach


(5-10 mins.)

When you arrive at the beach, review student predictions about what they might see on the beach.

Tell the students to: “Put on your sea goggles! Watch carefully! What do you see?


(15 mins.)

Lead students to a portion of a beach area at the lowest possible tide. Provide them the opportunity to explore on their own or in pairs with the focus questions:
What shells and other structures can you observe? What are they being used for by the animal?

Distribute buckets and magnifying boxes to chaperones to help students collect shells, animals and plants to investigate. Provide them also with cameras to take pictures of students and their finds.

Describe clear boundaries for the exploration and a signal you will use to bring them back together.


(30 mins.)

After you bring the group back together, divide the class into groups of 4-5 students. Give each group quadrat squares for each student. Review the use of the sampling device and its purpose in taking a sample of all of the plants and animals in the same area (amount of space) in different places on the beach. Students will each choose a spot to investigate, lay down the sampler, and observe the plants and animals within their square or circle. The chaperone will circulate among the students, taking a photo of the sampled area for use in identification of animals and external structures and explanations of their use back in the classroom.


(30 mins.)

Upon return, show photos to students. Ask them to use their senses (pointing to the sensory structures – eyes, ears, nose, etc. - they used) to describe what they felt, saw, heard and smelled at the tide pools or beach. Ask: Do you have any questions you still wonder about?

Ask them to study the photo of their sampled area and identify animals, including ones that lived in an empty shell, and plants they noticed within their square. Pass out a What Did You Observe? Form to each student for them to write and draw to illustrate what they observed in their quadrat. They can either use names they have learned for species groups or make up descriptive names. The intent is to make a list of how many different animals and plants they observed.

Part 3: Shell Structure and Function

(45 mins./day, 3 days)


(Day 1: 20 mins.)

Look at pictures taken on the field trip, share field notes and discuss the shells students saw (review).
Discuss shell structure and how the parts of the shell function to protect the animal inside. Introduce or reinforce the vocabulary words “armor” and “home.” Create a K-W-L chart “How Animals Use Shells” as part of the class discussion.


(Day 1: 15-20 mins.) 

Tell students they will be going further to sort shells by structure and function. Divide the students into groups and distribute different kinds of shells (or pictures of shells) to each group to sort by characteristics related to structure (bivalve, univalve, chiton plates). As a class, discuss the possible functions of the different types of shells. (Examples: shells that move with the animals that live in them, shells that are used as homes that never move, bivalve shells that close up tight when the tide is out to keep the mollusk body wet as long as possible, bivalve shells that don’t close completely because a long, thick neck is used to burrow down into mud or sand, univalve shells with a small opening that can be closed tightly)

After students sort and discuss, ask them to share what they found out about the shells they observed with the class.


(Day 2: 30 mins.)

Invent-a-Shell Structure for Humans: Discuss how humans use structures to protect themselves which is a function of shells for most mollusks. Discuss what kind of problem that humans have that a hard shell-like structure could solve. (protecting soft body parts from getting injured, protection from bears and insects, staying dry during rain) Brainstorm a list of protective structures that are shell-like (helmets, atv riding gear, yurts, igloos). Have a helmet available if possible to allow children to try it on and imagine how it might protect them from rain, injury, etc.

Alaska Native cultural connections: Kayaks are an example of a traditional form of transportation along Alaska’s coast. Traditionally-designed kayak skins, spray skirts, hatch covers, and waterproof clothing used together had the opposite function of mollusk shells - they functioned to keep people dry while traveling on the water.


(Day 3: 30 mins.) Students use clay to create a sea animal. They draw a design for a shell to protect this sea creature. Students may then choose recycled materials and create this shell.


(15 mins.)

1. After brainstorming protective structures for humans that are shell-like, have students draw their own protective structure that is shell-like and write about what it would protect them from. Start with the prompt: “I could use this to protect me from ______ like the shell of a _______ protects a _________ from ______________.” and then explain the protective features that are like those of a mollusk shell.

2. After designing and creating a shell out of recycled materials, they explain how the shape of their model would function to protect the clay animal inside. This may be done in small groups or in front of the whole class.

Resources for Planning and Teaching a Field Trip
Seashells, Crabs and the Sea Stars: Take-Along GuideBy Christiane Kump Tibbitts   
Children's Books
Musty Crusty AnimalsBook series by Lola M. Schaefer   
Tidepool Creature Features to TreasureBy High Tech Elementary North Country Kindergarteners   
Seashells by the SeashoreBy Marianne Berkes   
JelliesBy Twig George   
Jonathan’s Blue WorldYouTube  
Related Resources for Cultural and Bilingual Education
Chaa Salíi: Beach (Haida)Grade Level K-1. Sealaska Heritage Institute. Developed in Ketchikan and Hydaburg. Includes study prints and cut outs of common beach animals.  
Eék: Beach (Tlingit)Grade Level K-1. Sealaska Heritage Institute. Includes study prints and cut outs of common beach animals. Activity #2 involving sorting shells into univalves and bivalves and provides Lingit vocabulary related to shells and their local and traditional use. The extension activity for this lesson plan highlights traditional uses of shells as buttons on button blankets, as inlays in carvings and bentwood boxes, and as attachments to many objects as charms or rattles. In traditional Tlingit custom, buttons are a symbol of wealth and abalone buttons are especially prized. Activity #5 in the SHI unit focuses on hermit crabs. 
Our Ocean Resources (Alutiiq) Grade 1  
What Did You Observe? Form  
Teacher Background

For background information on univalve and bivalve mollusks, see Meet the Invertebrates.

In preparation for the field trip, students will have opportunities to observe a variety of mollusk shells in the classroom to prepare them for a rocky beach field trip where they will be able to observe and compare external structures of a variety of mollusks and other beach animals and plants and make inferences about their function. For more background on the biology of marine invertebrates and a source for line drawings, see Marine Invertebrate Background Information.

The assessment tasks address the NGSS performance expectation related to the Disciplinary Core Idea of structure and function of external parts of plants and animal.The second part of the NGSS Disciplinary Core Idea emphasizes the function of sensory structures to convey different types of information important for growth and survival. Due to the difficulties of being able to see both underwater and out of the water, intertidal animals rely much more on smell and taste. The structures they use, however, are small and often spread out all over their bodies. Instruction to deepen conceptual understanding will likely require observations of vertebrate animals with more obvious external sensory structures like eyes, ears, noses, and/or tongues.

After students engage in the sorting activity for univalves and bivalves, you can extend the learning by focusing student observations of similarities in external structures with similar functions. This will allow students to begin grouping organisms with similar structures as well as begin building their understanding that similar structures have evolved to meet the challenges of survival. Examples of external structures that are defining characteristics for classification of marine invertebrate phyla include the single foot of mollusks, the jointed legs of crustaceans, and the tube feet of echinoderms, all of which function in locomotion; and the tentacles with stinging cells of the cnidarians (sea anemones and jellies) that function to capture prey. Their observations of similarities and differences will also lay the foundation for concepts related to inheritance of traits and survival through adaptation that are emphasized in later grades.

Different types of bivalve shells provide protection against predators in different ways:

Both hard-shelled and soft-shelled bivalve clams burrow below the sand to hide, but only hard-shelled clams have thick shells that can clamp tightly closed and are resistant to cracking by predators. Some clam species are “gapers,” and are unable to retract their neck into the shell. Thin-shelled bivalves like scallops can swim to safety. Mussels live gregariously, tightly crowded together on rocks, and produce sticky byssal threads to tie themselves together. For more information about the structure and function of bivalve shells, see Reading Information from Empty Shells.
Diversity of protection against predator

In the primary grades, the NGSS emphasize observations of patterns and a foundational understanding of relationships between the external structures and their functions for plants and animals. The emphasis is not on classification for the sake of grouping and naming. The NGSS specifically exclude assessment of knowledge of animal species names in primary grades, however, learning Alaska Native names of culturally-important animals and animal groups receives emphasis in bilingual education in primary grades in the some Alaska school districts. Teachers should use their judgement in terms of the emphasis placed on assessing learning about the scientific or common names of different species or species groups.More background information on shells: Mollusk shells are exoskeletons. They are considered external parts although they have three distinct layers and continue to grow to accommodate the growth of the mollusk body. They’re composed mostly of calcium carbonate with only a small quantity of protein--no more than 2 percent. These shells, unlike typical animal structures, are not made up of cells. Mantle tissue that is located under and in contact with the shell secretes proteins and mineral extracellularly to form the shell. Think of laying down steel (protein) and pouring concrete (mineral) over it. Thus, seashells grow from the bottom up, or by adding material at the margins. This pattern of growth results in three distinct shell layers: an outer proteinaceous periosteum (uncalcified), a prismatic layer (calcified) and an inner pearly layer of nacre (calcified).

Prior Student Knowledge and Skills: Students should be able to work cooperatively in groups of 2-4 and record and communicate their observations with simple drawings and words. The emphasis for the kindergarten Sea Week field trip is on observing and noticing patterns in the types of places where plants and animals can be observed in relation to what plants and animals need to survive. Students should have a basic understanding about what is living and nonliving on the beach.

Possible learner preconceptions, misconceptions and instructional clarifications:

Learner Preconception/misconception: Students may be confused about whether shells are “living” and may not be aware that shells are part of the mollusk, not a separate structure like the shell “house” of a hermit crab.

Instructional Clarifications: Emphasize that a mollusk shell is a part of living animal that grows bigger as the rest of the mollusk grows, and when the animal dies, the shell dies too. When another animal like a hermit crab uses a shell as a home, it’s still dead.Students of this age may not be able to understand the relationships of internal and external structures, but you can show them diagrams to help them envision the various parts of different mollusk species, emphasizing the shell and foot structures as external.

Components of Next Generation Science Standards Addressed

Science & Engineering Practices

Constructing Explanations and Designing Solutions

Use materials to design a device that solves a specific problem or a solution to a specific problem. (1-LS1-1)

Disciplinary Core Ideas

LS1.A. Structure and Function

All organisms have external parts. Different animals use their body parts in different ways to see, hear, grasp objects, protect themselves, move from place to place, and seek, find, and take in food, water and air. Plants also have different parts (roots, stems, leaves, flowers, fruits) that help them survive and grow. (1-LS1-1)

LS1.D. Information Processing
Animals have body parts that capture and convey different kinds of information needed for growth and survival. Animals respond to these inputs with behaviors that help them survive. Plants also respond to some external inputs. (1-LS1-1)


Cross-Cutting Concepts

Structure and Function

The shape and stability of structures of natural and designed objects are related to their function(s). (1-LS1-1)

Influence of Science, Engineering, and Technology on Society and the Natural World

Every human-made product is designed by applying some knowledge of the natural world and is built using materials derived from the natural world. (1-LS1-1)


Common Core

W.1.7 – Participate in shared research and writing projects (e.g., explore a number of “how-to” books on a given topic and use them to write a sequence of instructions). (1-LS-1)
Alaska Cultural Standards
Culturally-knowledgeable students demonstrate an awareness and appreciation of the relationships and processes of interaction of all elements in the world around them.
Developed by Molly Reggiani and Laura Hanson, Cordova School District. Adapted for Sea Grant by Marilyn Sigman.
Last Updated on
Last Updated by
Marilyn Sigman
Alaska Sea Grant University of Alaska Fairbanks Alaska Department of Education and Early Development NOAA