Arthropoda (Crustaceans, Insects)

Phylum Arthropoda (Insects, Crabs, Lobsters, Copepods, Spiders, Scorpions, Horseshoe Crabs, Centipedes, Millipedes, Barnacles, Shrimp)

Wikipedia Entry

Approximate Number of Species:  1,097,289

Largest:  Pseudocarcinus gigas, the Tasmanian Giant Crab, obtains a carapace width of 1.5 feet (0.46 meters)

Tasmanian giant crab : Photo by Bess Grant via Flikr

Smallest:  Stygotantulus stocki, a minute parasite on copepods, only reaches a length of 0.004 inches (0.095mm)

References:

Brusca RC & Brusca GJ (2003) Invertebrates (Sinauer Associates, Inc., Publishers, Sunderland, MA) 2nd Ed.

Martin JW & Davis GE (2001) An Updated Classification of the Recent Crustacea (Natural History Museum of Los Angeles County, Los Angeles).

Boxshall G & Huys R (1989) New tantulocarid, Stygotantulus stocki, parasitic on harpacticoid copepods, with an analysis of the phylogenetic relationships within the Maxillopoda. Journal of Crustacean Biology 91:126-140.