Educational diagram illustrating the features and life cycle of Cnidaria, focusing on Obelia.

Let’s solve this step by step.

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Part A: Match the correct characteristics of Cnidaria

Cnidaria includes animals like jellyfish, sea anemones, and corals. Let’s go through each option and decide if it applies:

1. No body cavity → ✔ True. Cnidarians don’t have a coelom (body cavity). They are simple animals with just two layers of cells.
2. Simple structure → ✔ True. Their bodies are basic — no complex organs or systems.
3. Asymmetrical → ✘ False. Most cnidarians have radial symmetry (like a wheel), not asymmetry.
4. Diploblastic → ✔ True. They have two germ layers: ectoderm and endoderm.
5. Dimorphism → ✔ True. Many cnidarians (like Obelia) have two forms: polyp and medusa.
6. Endoskeleton → ✘ False. They don’t have internal skeletons. Some have hard outer parts (like coral), but that’s exoskeleton-like, not endoskeleton.
7. Cnidocyte → ✔ True. These are stinging cells unique to cnidarians.
8. Tentacles → ✔ True. All cnidarians have tentacles around their mouth for catching prey.
9. Radial symmetry → ✔ True. Their body parts radiate from a central point.
10. No true tissue → ✘ False. They DO have true tissues (epithelial, nerve, muscle-like cells), even though they’re simple.

So, the correct matches are:
- No body cavity
- Simple structure
- Diploblastic
- Dimorphism
- Cnidocyte
- Tentacles
- Radial symmetry

*(Note: “No true tissue” is incorrect — they do have tissues. “Asymmetrical” and “Endoskeleton” are also wrong.)*

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Part B: Label the Obelia life cycle

Obelia has a colonial polyp stage and a free-swimming medusa stage. The life cycle goes:

Polyp colony → produces medusae sexually → medusae release sperm and egg → fertilization → zygote → develops into planula larva → settles and grows into new polyp colony.

Looking at the diagram labels:

Top row (left to right):

- First box points to the feeding polyp on the left side of the colony → Feeding polyp
- Second box points to the reproductive polyp (with buds forming medusae) → Reproduction polyp
- Third box points to the adult medusa (jellyfish form) → Medusa

Bottom right:

- Box pointing to the fused egg + sperm → Zygote
- Box pointing to the early developing stage after zygote (before becoming swimming planula) → This is likely the Blastula stage (early embryonic development)

Wait — let’s check the sequence again:

After fertilization:
→ Zygote → Blastula → Planula → Settles → New colony

In the diagram:

- “egg” + “sperm” → arrow to a cell labeled with a box → that should be Zygote
- Then next stage (still round, before becoming elongated planula) → that’s Blastula
- Then “swimming planula” → then “planula” settling → then “starts new colony”

Also, the large purple creature on top right is the Medusa

The two types of polyps in the colony:

- One with long tentacles → Feeding polyp
- One with short stalks producing medusae → Reproduction polyp

So labeling:

Top row (left to right):
1. Feeding polyp
2. Reproduction polyp
3. Medusa

Bottom right:
4. Zygote (after egg + sperm fuse)
5. Blastula (next developmental stage before planula)

But wait — looking at the diagram again:

There are 5 boxes total to label.

From left to right, top to bottom:

Box 1 (pointing to polyp with long tentacles) → Feeding polyp

Box 2 (pointing to polyp budding off medusae) → Reproduction polyp

Box 3 (pointing to adult medusa) → Medusa

Box 4 (pointing to the cell right after egg+sperm fusion) → Zygote

Box 5 (pointing to the next stage after zygote, before swimming planula) → Blastula

Yes, that fits.

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Final Answer:

Part A Correct Characteristics:
- No body cavity
- Simple structure
- Diploblastic
- Dimorphism
- Cnidocyte
- Tentacles
- Radial symmetry

Part B Labels (in order as shown in diagram):
1. Feeding polyp
2. Reproduction polyp
3. Medusa
4. Zygote
5. Blastula