Read Stinging Cells, Comb Rows and Cnidarian Forms
Cnidarians capture prey with nematocysts, while ctenophores swim with comb plates; representative genera are common identification cues.
Living-system questions are solved by matching a structure or organism to its function, process and stated condition.
Separate the phyla
Cnidarians have cnidoblasts containing nematocysts used in prey capture and defence. Ctenophores use eight rows of comb plates and often show bioluminescence; they have adhesive colloblasts rather than cnidoblasts.
Remember the examples
Physalia is Portuguese man-of-war; Adamsia sea anemone; Pennatula sea pen; Gorgonia sea fan; Meandrina brain coral; Aurelia jellyfish. Obelia alternates polyp and medusa generations (metagenesis), though the particular diagram-referencing sample remains held until its missing figure is restored.
Trace Obelia metagenesis
Read the direction of the cycle: attached polyp colony → asexual budding → free-swimming medusae → sexual reproduction → larva → new polyp colony. In Obelia, this alternation of the asexual polyp and sexual medusa forms is metagenesis; it is not metamorphosis.
OlympIQ exam lens
- ✓Cnidaria: cnidoblast/nematocyst.
- ✓Ctenophora: comb plates, often bioluminescent.
- ✓Obelia: polyp–medusa metagenesis.
- ✓Aurelia: jellyfish; Gorgonia: sea fan.
Cnidarians sting; ctenophores capture prey with colloblasts.
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