Phylum Cnidaria

Free Response

Explain the function of nematocysts in cnidarians.


Nematocysts are “stinging cells” designed to paralyze prey. The nematocysts contain a neurotoxin that renders prey immobile.

Compare the structural differences between Porifera and Cnidaria.


Poriferans do not possess true tissues, while cnidarians do have tissues. Because of this difference, poriferans do not have a nervous system or muscles for locomotion, which cnidarians have.

Compare the differences in sexual reproduction between Porifera and Cubozoans. How does the difference in fertilization provide an evolutionary advantage to the Cubozoans?


There are two key differences between Porifera (sponges) and Cubozoans (box jellyfish) – gamete production and fertilization strategy. Box jellyfish have separate sexes, while a single sponge can produce both types of gametes. Box jellyfish also undergo internal fertilization, while sponges reproduce by external fertilization. Internal fertilization allows box jellyfish to control which sperm is used for fertilization and increases the likelihood of ova and spermatozoa meeting.