Sea Spider

This one is around 1.5 cm from tip of leg to leg, the body (if there is any) is just around 0.5 cm. There is a tiny Copepod (Parasite) taking a ride on this Sea Spider (Pic#2 & Pic#3)
Not only are they difficult to find/spot because of their size, but they are also master of camouflage by collecting algae and/or small anemone to attached to their legs.

Sea spiders have long legs in contrast to a small body size. The number of walking legs is usually eight (four pairs), but species with five and six pairs exist. Because of their small size and thin body and legs, no respiratory system is necessary, with gases moving by diffusion. A proboscis allows them to suck nutrients from soft-bodied invertebrates, and their digestive tract has diverticula extending into the legs.