Phylum Tardigrada (Water Bears)
Approximate Number of Species: 800
Largest: Thulinia ruffui at a length of 0.035 inches (0.9 mm)
Smallest: Ligiaritus eastwardi at a length of 0.008 inches (0.2mm)
References:
Higgins RP & Thiel H eds (1988) Introduction to the study of meiofauna (Smithsonian Institute Press, Washington, D.C.).
Brusca RC & Brusca GJ (2003) Invertebrates (Sinauer Associates, Inc., Publishers, Sunderland, MA) 2nd Ed.