Water fleas - Daphnia - are rather cute little freshwater arthropods:
In some circumstances (water temperature, presence of predators), rather than having that sharp little point on their heads (top of the picture, above the eyespot) some Daphnia will have a longer, spikier 'helmet'. And this is where it gets interesting: it depends on the mother. If a 'helmet-less' female Daphnia is in an environment where there are also predators, her offspring will sport helmets. If not, they won't. This observation has been described in one article as an example of Lamarckian inheritance.
But it's not. It's an example of epigenetics in action. And PZ does his usual excellent job of explaining what's going on, & why the original story was so far off the mark. As he says, "Genes don't execute rigid, predetermined programs of development — they are responsive to the environment and can express radically different patterns in different contexts." And this is what's happening with the waterfleas (where the contexts are presence & absence of predators). Great stuff.