FruitlessFetusSign upYour fetus has just caught up to a fairy shrimp, Branchinecta lindahli, a delicate freshwater crustacean about 12 mm long that swims upside down, beating eleven pairs of leafy legs in a rippling wave. It lives in temporary pools, from desert rain puddles to snowmelt ponds, that hold water for only a few weeks.
Their real trick is patience. When a pool dries up, the adults die, but their eggs, called cysts, can sit in dry dust for years or even decades, surviving heat, freezing, and drought, then hatch within hours when the rains return.
They are a whole animal built around waiting for exactly the right moment to appear, which is a feeling you may be getting to know. They are also close cousins of the brine shrimp sold as sea-monkeys.
Meanwhile, inside you
Your embryo this week is sprouting the paddle-like beginnings of arms and legs, the same ancient limb blueprint that every four-limbed vertebrate shares.