DEF: "Organism subdivision which is the collection of anatomical structures on the body surface."
1. The definition makes it sound like a surface structure is the collection o all structures on the surface; this would make e.g. naris part_of a surface structure, rather than is_a, as is currently the case.
This is rectified by changing the text def to "Organism subdivision that is an anatomical structure on the body surface."
2. There have been objections to surface structure being a type of organism subdivision, which I would agree with. I suppose the most immediate parent would be "anatomical structure"; but maybe this is a CARO issue.
3. It seems odd to say that a fin (currently a SS) is "on" the surface. I think make classes like this directly organism subdivisions? Organism subdivisions always have a surface that is continuous with the surface/integument of the organism.