so one reptile can have one or more different morphs related to it,
That "more" makes this a many to many relationship between reptiles and Morphs. A given Morph record can be linked to many Reptile records and a given Reptile record can be linked to more than one Morph record.
That requires a join table to facilitate the many to many relationship:
Reptile::Record_ID = Reptile_Morph::Record_ID
Morphs::Morph_ID = Reptile_Morph::Morph_ID
A portal to Reptile_Morph can be placed on your Reptile layout to list all Morphs identified for that reptile. Fields from the Morphs table can be included in this portal row to supply the needed details.
In similar fashion, a portal to Reptile_Morph on the Morphs layout will list all Reptiles identified as having that Morph.
Here's a demo file that illustrates a many to many relationship. Check out the "basic set up" first to see how you can set this up and then investigate the more advanced options if you are so inclined: http://www.4shared.com/file/dZ0bjclw/ManyToManywDemoWExtras.html