Out for a lunchtime stroll on the waterfront in Liverpool today, I was fortunate enough to get an unusually close-up view of one of my favourite birds, a curlew [Numenius arquata], digging for lugworms [Arenicola marina].
An odd thought then occurred to me: how do lugworms manage to breathe when the tide is in? Equally to the point, how do they avoid drowning?
It turns out that lugworms have external gills for breathing underwater. I must have dug up hundreds of them for bait as a child, but I had never noticed their gills. Well, actually, that's not true: I had noticed their gills; I just hadn't realised that they were gills.
But now I know.