by Polly Walter
Here are two lessons I developed for my grade 2 class on dissecting squid. It is a very popular activity with them, and I think they learn a lot about the biology of squid and other living organisms, as we always get into comparative discussions. ItÕs smelly, but fun!
Studying squid has been a real highlight in our science program for several years. The reason is that we study real squid; itÕs a Òhands onÓ lesson with children examining the actual animal, dead but real. It turns out that squid are cheap and readily available in most supermarket frozen food departments: 24 frozen calamari (under $5.00) are enough for one class session of discovery and fun. Just soak the box of squid for a few hours to thaw them, and they are ready to use.
Our squid lessons have always been part of a larger study of the sea. We talk about food webs, zones of life, vertebrates and invertebrates to give a context for where squid fit in .
Before we do the dissecting lessons, we usually go through some or all of the following steps:
Squid are amazing! Here are some of the fascinating facts we learn:
They are the second most plentiful animal (after fish) in the ocean.
They are cephalopods which is Greek for Òhead footÓ. They have a mantle with 2 fins, 8 arms and 2 tentacles (used for grabbing prey).
They have beaks that can cut wire, and eyes on the sides of their head which give 180 degree vision on each side and give them the best vision of all invertibrates.
Their eyes are similar to ours with a lens which the children can find. They range in size from 2.5 cm to 18 m.
They have a variety of color spots on their back which enlarge depending on the color the squid chooses to be.
Some have photophores in their skin which give off light to attract prey, locate a mate, illuminate the way, or confuse enemies.
They move by jet propulsion, allowing water into their mantle and forcing it out through their siphon. They use their siphon and fins to make quick changes in direction. Some can even fly through the air.
They have three hearts: one for their body systems and one located at the base of each gill so that they can pump oxygen to their muscles quickly, thus enabling them to swim fast.
Their nerve fibers are very large compared to human nerve fibers, enabling them to carry messages at 50 mph compared to 4.5 mph in humans.
They feed at night in schools near the surface, eating plankton, fish, other squid, and crabs .
The male sex arm is fourth from the left with little finger projections at the tip.
During mating season, squid congregate at the surface of the sea. Males take a small package of sperm on the sex arm and fit it under the mantle of a female, next to her eggs. The squid that we dissect were caught at the surface of the water during the mating season so that eggs and sperm are very prominent.
Their predators are penguins, other squid, eels, toothed whales, seals, jellyfish, fish, and humans. Giant squid live very deep in the ocean and are eaten by sperm whales.
For defense, they can squirt out a cloud of ink, change color to match their surroundings, make a jet propelled escape, maneuvre quickly, bite with their beak or fly through the air.
Look at general diagram of squid.
Identify and list the things the students will look for on their squid.
Cover the desks or tables with newspaper and hand out trays and squid.
On the outside of the squid look for:
Let the children explore to find what we listed and anything else they might discover. Afterwards, discuss what they found. Ask questions like, ÒWhat did you find?Ó ÒWere there any surprises?Ó ÒWhat was hard to find?Ó ÒWhat would you do differently next time?Ó
The same materials are used, but the overheads on the squid anatomy are more detailed.
Show the overhead of the anatomy of the male and female squid, and discuss what they found last time and what they will find this time. Suggest that they be really careful this time, like real scientists, and be very careful about how they observe their specimens.
Some children will enjoy displaying the different parts that they find on their meat tray.
Things to look for the second time:
Have the children share what they found through discussions and displays.
I ask them to reflect on how the dissection went that time. How it was different? How it was the same? What they were pleased about? What went better the second time? What else they are still curious about?
I find the children have a more focussed attitude the second time we dissect the squid. They are more careful and observant. They like the second time better, and their understanding deepens.
Polly teaches 2nd Grade at Gorden Head, Victoria, BC Canada.
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