Hi!
Documentation for the GGBN API is work in progress. Some examples in advance:

API URL: http://www.ggbn.org/ggbn_portal/api/search?

getCounts	total counts of different taxon levels and sample types (used for the start page)
getSampletype&name=Arthropoda	total counts of sample types for a certain name (any level)
getClassification&name=Chordata	total counts of samples for all children of a name

Feel free to test it. If you have any questions please contact support@ggbn.org. More information will follow soon.