Kabir's grandmother still uses a natural bath sponge…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Kabir's grandmother still uses a natural bath sponge. It is soft, full of holes, and soaks up water fast. (a) To which phylum did the living animal belong? (b) What is the soft skeleton made of? (c) In the living sponge, which openings let water in, and which one let it out?
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 phylum. The bath sponge, Euspongia, belongs to Porifera.
Step 2. The skeleton. A soft bath sponge has a skeleton of spongin fibres. Hard spicules would scratch the skin.
Step 3. The canal system. In life, water came in through the many small ostia, passed through the spongocoel, and went out through the osculum.
Answer: (a) Porifera; (b) spongin fibres; (c) in through the ostia, out through the osculum.
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