Smallest Mammal — Shrew Smallest Bird — Humming bird of cuba (5.5 cm) Smallest ape — Gibbon Smallest bone — Stapes Smallest Cranial Nerve — Abducens Smallest R.B.C. — Musk Deer (2.5 tm) Smallest primate — Lemur Smallest snake — Lepto typhlops Smallest Salamandra — Desmograthus Smallest freshwater fish — Pandaka Smallest marine fish — Goby fish 8-10 mm in length Smallest Insect — Mymer Smallest Protozoan — Baberia Smallest Muscle — Arrector pilli or stapedius muscle Smallest Annelid — Chaetogaster Smallest virus — Foot mouth virus of cattle Smallest Phylum — Porifera Smallest class — Amphibia Smallest cell — Squamulla Smallest bacteria — Dialister