Barnacles and Copepods; Maxillopoda

Most of the Barnacles look externally rather like a small, limpet style of sea snail with a hole in the top, but they are actually non-moving, filter-feeding crustaceans.
Totally different are the Copepods – tiny creatures, rarely seen on scuba dives because they are so small, mainly photographed as parasites on a Phyllidid Nudibranch and a Hypselodorid as well as hanging out on an unidentified sponge and an algae.

Looking more like small shellfish with feathers !

Small cryptic beasties - ours seem to be mainly associated with Nudibranch.