Macro Practice III

What friends predicted happened last Sunday morning: someone scrambled down the rocks to check if this figure lying motionless in a shallow pool was dead or alive. Luckily, I was feeling very alive indeed, watching a sizable Spiny starfish Marthasterias glacialis moving over the rocks using its hydraulic tube feet. A beautiful blue-grey colour, the surface of these animals are very richly textured. I am not sure exactly what is going on at the tips of the arms: the very end shows a red organ, potentially light sensing. It is surrounded by nodules, which might be the precursors of the centres of new plates covering its body, or something else. The tube feet at the tips are smaller and orange-tinged and I am again not sure whether they are just newly developing or having special sensory functions. I noticed the madreporite at the top of the animal: this sieve plate is involved in pumping the water in the body for hydraulic locomotion. It resembles a stony coral ‘madrepore’ colony, hence its name. In general, the seastar surface resembles a coral I think. The photos are nice, but I know I could do a lot better: next time!

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