For example, there are seven pairs of apparently almost identical marine snapping shrimp (Alpheus) populations on either side of the Isthmus of Panama, which did not exist until about 3 million years ago.
It is believed that closure of the Central American seaway by the rise of the isthmus that is now Central America created distinct zones for coral growth and zooxanthellae specialization.
After the external examination is done cut the fish carefully (to avoid cutting organs or major vessels) from vent to isthmus to expose the internal organs.
mouth large and bordered by premaxilla and maxilla; pore (foramen) in axil of pectoral fin in some; pelvic fins jugular (in front of pectorals), with one spine and two or three soft rays; three pairs of gills; gill membrane broadly joined to isthmus; ...
 See also: Fish, Species, Water, Origin, Temperature
  
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