Smallest organisms with mature females measuring as little as in standard length. This fish, a member of the carp family, has a translucent body and a head unprotected by a skeleton. The one of world's smallest fish based on the minimum size at maturity is "Schindleria brevipinguis" from Australia,their females reach it at 7 mm (0.28 in) and males at 6.5 mm (0.26 in), Males of "S. brevipinguis" have an average standard length of , a gravid female was . This fish, a member of the goby family,its first anal-fin ray further forward, under dorsal-fin 4. Male individuals of the anglerfish species
Smallest organisms on the archaeon "Ignicoccus"; it must be in contact with the host organism to survive. Prasinophyte algae of the genus "Ostreococcus" is the smallest free-living eukaryote. The single cell of an "Ostreococcus" measures only 0.8 μm across. Several species of Myxozoa (obligately parasitic cnidarians) never grow larger than 20 µm. One of the smallest species ("Myxobolus shekel") is no more than 8.5 µm when fully grown. The shell of the nut clam "Condylonucula maya" grows only 0.54 mm long. The smallest water snail (of all snails) is "Ammonicera minortalis" in North America, originally described from Cuba. It measures 0.32 to