title for tubeworm learn-about section in A SNAILS'S ODYSSEY
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Explanations for answers to tubeworm-withdrawal quiz:

The worms can sense through their tube what the feeding/predator conditions are like outside and adjust their hiding times accordingly. This would be possible only if the calcareous tube were porous and the worms could sense food-related chemicals in seawater diffusing in.  Based on the solid, apparently impermeable construction of the tube this does not seem likely.

The worms are more tired on a low-ration diet and simply stay in their tubes longer after withdrawal. Possibly, and this is a point addressed by the authors.  On a high-ration diet the worms would certainly be more frisky and perhaps more inclined to pop out earlier.  However, this could still involve a “memory”, not necessarily a “cerebral”-type memory, but perhaps an ingestive-conditioning type of memory.  The worm is physiologically sated and associates this with its recent feeding experience, something done outside of the tube. 

The withdrawn worm samples the outside seawater for the presence of food and predators via the operculum and adjusts its hiding time accordingly. Such sampling via the operculum may be possible but has not been described.  The operculum appears to fit too tightly for water to be sampled around it.  Worms in their tubes do make tentative extensions as they start to emerge but, if this occurs in the study, it is not mentioned by the authors.

Greater concentration of food in the water reduces oxygen levels; thus, a worm that withdraws at this time will have incurred an oxygen debt that must be repaid and so it emerges quicker. Possibly, and is similar to the second answer above.  This point is put forward as an alternative explanation by the authors for their data, but they note that their measurements of oxygen levels in the experimental aquarium showed no food-related effects.

NOTE in T-maze learning tests with free-living or errant polychaetes such learning capability has only been weakly demonstrated

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