Phylum Echinodermata (Starfish, Urchins, Sea Cucumbers, Brittle Stars, Basket Stars, Sea Lillies)

Approximate Number of Species: 7,000

Largest: The starfish Thromidia catalai and Thromidia gigas can reach 3.2 lbs (6 kg). “Thromidia catalai-the South Pacific species reaches a maximum span of a little over 2 feet (60-65 cm). But Thromidia gigas, which occurs in South Africa was measured with a diameter of nearly 70 cm!” via Echinoblog

thromidia seastar Treamy1 Flikr — Thromidia spp: Photo by Treamy1 via Flikr

Smallest: The sea cucumber Parvotrochus belyaevi at 0.06 inches (1.5 mm)

References:

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

Gage J & Billet D (1986) The family Myriotrochidae Theel (Echinodermata: Holothuriodiea) in the deep northeast Atlantic Ocean. Zoological Journal of the Linnean Society 83:229-276.