What exactly are invertebrates and why would you them in your tank?

A 'clean up crew' or pretty 'flowers'

Well sort of! The definition of an invertebrate is an animal without a spinal column. For a marine tank, you can think of them as ‘clean up crew’ which will clean your tank for you e.g. Turbo Snails or ‘flowers’, something colourful and pretty to site in you tank e.g. finger corals.

Orange Polyps amoung pink Sponges