Not an embryo.

I just finished teaching a marine invertebrate embryology course (hence the long hiatus). So I thought I'd post a picture of something that is not an embryo, but budding embryologists often confuse with an embryo in the middle of first cleavage. In fact, Noctiluca is a Dinoflagellate which (confusingly) doesn't look much like a Dinoflagellate. It's really big, buoyant, and has a single, long, mobile tentacle.