What is the name of lower Invertebrates that have a jelly-like layer between endoderm and ectoderm?

What did the first language sound like

The image shows the evolution of a species of fish. a few fish from a population developed different social behaviors and evolved into different species. two fish according to the image, the fish underwent . the new species of fish had mating seasons that were different from that of the original fish. because of the differences in mating seasons, the fish underwent reproductive isolation. this mode of isolation would be .

The function of the ciliary escalator is to