Ectoparasite
The medical term for an organism that lives on the outer surface of the host is "ectoparasite." Examples include lice and ticks.
A Sea Turtle
medical term: Ganglion Cyst
The curved outer surface of a circle is the perimeter.
The outer surface of the bone is called the periosteum.
ep·i·der·mis /ˌepiˈdərmis/NounThe outer layer of cells covering an organism, in particular.The surface epithelium of the skin of an animal, overlying the dermis.Synonymscuticle - scarfskin
pellicle
they have coating of wax on the outer surface of their body
Of or relating to the surface or outer part of a body or organ; external.
lining
cuticle
Its a crab!
From a medical aspect, the surface of the skin is only a very small portion of the body. Surface blemishes are shallow and do not extend into the lower dermal layers. If one strips off the outer layer, they are left with perfection only a few millimeters below the surface.