Cnidaria

Question 1

Where in the phylogeny by Brusca et al. are the cnidarians located?

Answer 1

Cnidarians are located within the Eumetazoa, which are animals with true tissues.
They are one of the earliest-diverging groups of eumetazoans and are placed as
the sister group to Bilateria

Question 2

What are synapomorphies of cnidaria?

Answer 2

cnidocytes

radial symmetry

diploblastic tissue layers

gastrovascular cavity

Question 3

What are the subphylum of cnidaria?

Answer 3

Medusozoa – Includes cnidarians with a medusa stage in their life cycle.

Anthozoa – Contains cnidarians that exist only as polyps (no medusa stage).

Question 4

What are found in Medusozoa? (4)

Answer 4

Scyphozoa (true jellyfish)
●
Cubozoa (box jellies)
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Hydrozoa (hydroids, some jellyfish-like species)
●
Staurozoa (stalked jellyfish)

Question 5

What are the groups in Anthozoa (3)?

Answer 5

Hexacorallia (Zoantharia) – Sea anemones, hard coral
●
Octocorallia (Alcyonaria) – Soft corals, sea fans, sea pens
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Ceriantharia – Tube anemones

Question 6

How do cnidaria develop, feed, and move?

Answer 6

Most have a polyp (sessile) and medusa (free-swimming) stage.

Feeding: Carnivorous; use tentacles with cnidocytes to capture prey and bring it to
the mouth.

Movement: Use pulsations (medusa) or contract muscles (polyp); coordinated by
a nerve net.

Question 7

How do cnidarians reproduce, and where do they live?

Answer 7

Reproduction: Sexual (medusa release gametes) or asexual (budding in polyps).

Habitat: Marine, from shallow reefs to deep-sea environments. Some hydroids
live in freshwater.

Question 8

What structures do cnidarians possess that were not present in poriferans? (4)

Answer 8

True tissues (sponges lack organized tissues).

Nerve net for coordinated movement (sponges lack nerves).

Mouth and gastrovascular cavity (sponges filter feed through pores).

Cnidocytes for prey capture (sponges lack specialized stinging cells).

Question 9

What are the subclasses of anthozoa (3)?

Answer 9

Hexacorallia (Zoantharia) – Sea anemones, hard corals, black corals

Octocorallia (Alcyonaria) – Soft corals, sea fans, sea pens

Ceriantharia – Tube anemones

Question 10

What life stages are present for the anthozoans?

Answer 10

Only Polyp Stage: Anthozoans do not have a medusa stage (unlike jellyfish).

Question 11

What methods of reproduction are
present in anthozoa?

Answer 11

Sexual – Polyps release sperm and eggs, leading to a planula larva that settles and
grows into a new polyp.
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Asexual – Budding or fragmentation to form colonies.

Question 12

Which characteristics allow you to identify members of anthozoa? (4)

Answer 12

Hexacorallia – Tentacles in multiples of 6 (e.g., stony corals, anemones).

Octocorallia – Tentacles in multiples of 8 (e.g., soft corals).

Calcium Carbonate Skeletons – Found in stony corals (Hexacorallia).

Symbiosis – Many have mutualistic relationships with zooxanthellae algae, aiding
in reef building.

Question 13

Whaat characteristics allow you to identify the subclasses of coral (3 each)

Answer 13

Hexacorallia (Zoantharia) – Stony corals & sea anemones
- 6 tentacles (or multiples of six)
- Hard skeleton (stony corals)
- Solitary (anemones) or colonial (corals)

Octocorallia (Alcyonaria) – Soft corals, sea fans, sea pens
- 8 tentacles (usually feathery)
- Soft, flexible skeleton
- Always colonial