Actually, MorphMarket knows about more genes and subcategories than are listed, but we don't show search tags which have no results. To make this more obvious, you can now see the subcategories which are currently empty (red arrow in image).
On occasion, you may want to list an animal which doesn't exactly fit into these subcategories either. For that reason we've just added "Other" subcategories in the Other Pythons, Other Boas, and Other Colubrids areas. This is shown above by the the purple arrow, where the "Other" bucket has some Ringed and Scrub Pythons.