To accompany the lecture series Evolution: Constant Change and Common Threads.
The young starlet sea anemone forms tentacles by cell division, migration, and shape changes.
... but that's not all they'll do. Several genes determine the diverse shapes and functions of crustacean appendages.
This short-tailed fruit bat embryo shows a pattern of bones in its limbs characteristic of all tetrapods: one bone, two bones, lots of bones, digits.
During the larval stage, the Nemertean worm develops inside a hollow sac from which the juvenile eventually emerges, rupturing the sac and then eating the remains.