Goliath

Beware of questions like "Goliath is the world's largest variety of what creature?"

The goliath frog is the world's largest frog; but the goliath heron is the world's largest heron; the five species of goliath beetles are probably the world's heaviest insects, if not the longest. The goliath shrew, however, is not the world's largest shrew; that honour goes to the the Asian house shrew, which is about 15 cm long and weighs around 100 g. The goliath coucal is a species of cuckoo, though whether it's the world's largest or not I haven't been able to ascertain.

The goliath birdeater isn't even the world's biggest spider, by leg span. The giant huntsman spider, which was discovered in a cave in Laos in 2001, can be up to a foot (30 cm) across. Although the goliath birdeater runs it very close (also said to have a legspan of up to, and sometimes exceeding, 12 inches), most sources seem to agree that the giant huntsman just has it.

Seems to me that the safest answer to the question that I started this note with is "frog". For the answer to be "spider", the question would have had to include the word "birdeater". ("Heron" is an option, but that would, IMHO, be too specific.)