On a beach in Goa, a tourist steps near a blue, balloon-like animal washed up on the sand…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
On a beach in Goa, a tourist steps near a blue, balloon-like animal washed up on the sand. A lifeguard warns her not to touch its long tentacles, even though the animal looks dead. (a) Name the animal and its phylum. (b) Which cells make the tentacles dangerous, and what do they hold? (c) Give two uses of these cells to the animal.
Need a reminder? The key ideaShow
Porifera: cellular level; water enters by ostia, passes the collar cells (choanocytes) in the spongocoel and leaves by the osculum; spicules or spongin; hermaphrodite. Cnidaria: cnidoblasts with nematocysts; gastro-vascular cavity with one opening; polyp (Hydra, Adamsia) and medusa (Aurelia); metagenesis in Obelia; Physalia, Pennatula, Gorgonia, Meandrina. Ctenophora: eight rows of comb plates, bioluminescence, only sexual reproduction; Pleurobrachia, Ctenoplana.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The animal. It is Physalia, the Portuguese man-of-war. It belongs to Cnidaria.
Step 2. The cells. The tentacles carry cnidoblasts (cnidocytes). Each holds a nematocyst, a stinging capsule that can still fire after the animal is washed ashore.
Step 3. Their uses. Cnidoblasts help in anchorage, defence and catching prey.
Answer: (a) Physalia, Cnidaria; (b) cnidoblasts, holding nematocysts; (c) any two of anchorage, defence and catching prey.
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