Diagram of the two stages in the cnidarian life cycle: polyp and medusa.

Explanation:
Let’s go through each question one by one, using basic biology knowledge about cnidarians (like jellyfish, sea anemones, and hydras).

1. What is a cnidarian?
A cnidarian is an animal in the phylum Cnidaria. They are simple, mostly aquatic animals with radial symmetry, stinging cells called cnidocytes, and two main body forms: polyp and medusa.

2. What important features unite the cnidarians as a group?
Key shared features:
- Radial symmetry
- Presence of cnidocytes (stinging cells) used for capturing prey and defense
- A single opening (mouth/anus) leading to a gastrovascular cavity
- Two tissue layers: ectoderm and endoderm, with mesoglea in between
- Nerve net (no central brain)

3. What are cnidocytes?
Cnidocytes are specialized stinging cells found only in cnidarians. Each contains a tiny harpoon-like structure called a nematocyst that can shoot out to inject venom.

4. A poison-filled, stinging structure within a cnidocyte that contains a tightly coiled dart is called a(n) ______.
This is the nematocyst — it’s the organelle inside the cnidocyte that delivers the sting.

5. The following sentence true or false? Cnidarians have bilateral symmetry.
False — cnidarians have *radial* symmetry (body parts arranged around a central axis), not bilateral (left/right mirror image).

6. What are the two stages in the cnidarian life cycle?
The two main body forms/stages are:
A. Polyp — usually sessile (attached), tubular, mouth up (e.g., sea anemone, hydra)
B. Medusa — free-swimming, bell-shaped, mouth down (e.g., jellyfish)

7. Write labels on each illustration below to name the different body parts.
Since we can’t see the image, but based on standard diagrams:
- The left drawing (labeled “Polyp”) typically shows:
• Tentacles (around the mouth)
• Mouth
• Body column
• Basal disc (foot for attachment)
- The right drawing (labeled “Medusa”) typically shows:
• Bell (umbrella-shaped body)
• Tentacles (hanging down)
• Mouth (on underside, often on manubrium)
• Gonads (reproductive organs, visible as rings or patches)
• Subumbrellar surface (underside of bell)

But since the question asks to *write labels*, and the student must do it on the worksheet, we assume they’re expected to identify the two forms:
→ Left = Polyp
→ Right = Medusa

Now, let’s verify answers:

Q1: Definition — correct as above.
Q2: Features — radial symmetry, cnidocytes, gastrovascular cavity, diploblastic, nerve net.
Q3: Cnidocytes = stinging cells.
Q4: Nematocyst ✔
Q5: False ✔
Q6: Polyp and Medusa ✔
Q7: Labels correspond to the two forms shown — Polyp and Medusa (already labeled in the diagram, so likely just confirming understanding).

Final Answer:
4. nematocyst
5. False
6. A. Polyp B. Medusa