Counting and using the four operations are essential number skills to be developed during the primary years. Use sea creatures and other natural objects to help your students.

Contents Lesson suggestions: 1. Counting 2. Counting with shells

1. Counting (Y1-2)

You will need… Models (and/or images) of: • Crab • Octopus • Sea stars • Fish • Bivalve mollusc • Sea snail

Not only does this exercise introduce your students to South Australian sea creatures, but it also introduces them to the correct terminology for body parts of particular creatures. For example, crabs have legs, but sea stars have arms.

This activity can be a verbal interaction or as an art exercise, with each student doing a drawing of one sea creature and then writing the number of something on the paper, e.g. do a picture of a sea star and write the number ‘5’ next to it, to indicate 5 arms.

Some suggestions:

How many legs does a crab have? [8] How many claws does a crab have? [2] (scientists say ‘one pair’)

How many tentacles does an octopus have? [8]

How many tentacles does a squid have? [10] (8 normal tentacles that are out all the time and 2 special tentacles used only for grabbing prey; they are kept rolled up inside the head)

How many arms do most sea stars have? [5] (usually; you will notice in the images that some sea stars have more than 5 arms; for example, there is a common purple sea star found around Adelaide that has 6 arms but 5 is the norm for most species.)

How many shells does an oyster/mussel/razorshell have? [2] (insert a bivalve that you think your students might know; students that fish often know about razorshells.) How many shells does a sea snail have? [1]

How many eyes does a fish have? [2] How many tails does a fish have? [1] How many nostrils does a fish have? [2] (Yes, fish have noses!) How many eyes does a sea star have? [0] (Trick question. Sea stars do not have ‘eyes’ as such and therefore cannot see in the sense that we can. They have very basic visual receptors on the ends of each arm that can detect light and shade, but that’s it.)

Extension Use pictures to help your students explore the four operations (+, -, x, ). For example:

• You found two crabs in a rockpool. How many legs are there in total? [16] • On the beach, you find one sea star with 5 arms and one with 6 arms. How many arms are there in total? [11] • You eat some seafood. On your plate, there are 2 mussels and 2 oysters. How many shells are there in total? (Hint: each mussel & oyster has 2 shells.) [8] • You go fishing and you catch one squid and one octopus. How many tentacles are there in total? (Hint: remember squid and octopuses have different numbers of tentacles.) [18]

2. Counting with shells

You will need… Lots of shells Black marker pen

Write single numbers on the inside or outside of the shells where it is easy to see. Write the operators (+, -, x, ) on shells or separate blocks. Use the shells to help your students count and add up. Keep them in a large box where students can access them during free time or maths time.

2 + 3 = 5

-- GregCollings - 09 Nov 2008