The youngsters of many marine organisms, both those with and without backbones, lead a life and conduct their survival, their feeding, their locomotion and their growth processes in a completely different way to their sexually mature adult forms. Invariably of course they are much smaller than the adults. Technically most are called larvae, because before they achieve adulthood they undertake such a fundamental change or series of changes that, just as a caterpillar becomes a pupa and then a moth, or a tadpole becomes a frog, so they too metamorphose from larval design and habit into adult, or at least juvenile, design and habit.

Many are born as eggs, some as live larval forms, some eggs are retained, hidden, disguised or fixed, others are shed into the surface waters and are therefore called pelagic eggs. From all the eggs, hatch pelagic larval forms or “water babies”.