Invertebrates: Mollusks worksheet - Free Printable

Let's solve the problem step by step using the diagram and information provided.

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a. From the examples given, name one mollusk that has each of the following features:

#### I. One shell
- Mollusks with one shell are typically gastropods, such as snails.
- In the diagram:
- Snail has a single spiral shell.
- Winkle also has one shell (it's a type of sea snail).
- Limpet has a single conical shell.
- Oyster has one shell (though it’s usually attached to a surface), but oysters are bivalves — wait, actually, oysters have two shells, but one is often not visible because it's cemented to a surface.

✔ So, correct answers for one shell include:
- Snail
- Winkle
- Limpet

👉 Choose one:
Answer: Snail

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#### II. Two shells
- These are bivalves — mollusks with two hinged shells.
- Examples in the diagram:
- Clam
- Scallop
- Mussel
- Oyster (yes, oysters have two shells, though one may be fixed)

✔ So, any of these would work.

👉 Choose one:
Answer: Clam

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#### III. No shells
- Mollusks without shells are soft-bodied and lack external protection.
- Examples:
- Slug – no shell (a land snail that lost its shell)
- Octopus – no shell
- Squid – no external shell (though they have a pen, which is internal)
- Cuttlefish – has an internal cuttlebone, but no external shell

Note: While squid and cuttlefish have internal structures, they are considered shell-less externally.

But the question asks for "no shells" — so we look for animals without any shell at all.

✔ Best answer: Slug or Octopus

👉 Choose one:
Answer: Slug

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✔ Final Answers for part (a):

I. one shell → Snail
II. two shells → Clam
III. no shells → Slug

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b. State TWO (2) ways in which snails and octopus are different. [2]

We need two differences between snails and octopuses.

Let’s compare:

| Feature | Snail | Octopus |
|--------|-------|---------|
| Shell | Has a hard, spiral shell | No shell |
| Movement | Crawls slowly on a muscular foot | Swims and moves using arms/tentacles |
| Habitat | Mostly land or freshwater | Ocean (marine) |
| Number of tentacles/arms | One (foot) | Eight arms |
| Body structure | Soft body with shell | Soft, flexible body with no shell |

So, two clear differences:

1. Snails have a hard shell, while octopuses have no shell.
2. Snails move slowly using a muscular foot, while octopuses use their eight arms to crawl or swim quickly.

✔ Acceptable answers:

Answer:
1. Snails have a shell, but octopuses do not.
2. Snails move slowly on a foot, while octopuses use their arms to move quickly.

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✔ Final Answer Summary:

a.
I. one shell → Snail
II. two shells → Clam
III. no shells → Slug

b.
1. Snails have a shell, but octopuses do not.
2. Snails move slowly using a foot, while octopuses use their arms to move quickly.

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This completes the worksheet correctly based on the diagram and biological knowledge.