Phylum Cnidaria (jellyfish, corals, hydroids, anemones)

Approximate Number of Species: 10,000

Largest: The largest noncolonial Cnidarian is the Lion’s Mane Jellyfish, Cyanea arctica, with a bell diameter of up to 5.6 feet (1.7 meters) and a tentacle length of 120 feet (36.6 meters). The largest colonial Cnidarian, that is not a coral reef, is the Bubblegum Coral, Paragorgia arborea that can reach heights of 9.8 feet (3 meters)

lions mane Flikr KaJ22 — Lion’s Mane Jellyfish – Photo via KaJ22 on Flikr

Bubblegum Coral Flikr NOAA — Bubblegum Coral – via NOAA on Flikr

Smallest: The smallest Cnidarian is the tiny hydra, Psammohydra nanna, with a height of only 0.02 inches (0.4 mm)

hydra Flikr Proyecto Agua — Hydra – photo via Proyecto Agua Flikr

References:

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

Higgins RP & Thiel H eds (1988) Introduction to the study of meiofauna (Smithsonian Institute Press, Washington, D.C.).

Peron F & Lesueur CA (1810) Tableau des caractères génériques et spécifiques de toutes les espèces de méduses connues jusqu’à ce jour. Annales Muséum national d’Histoire naturelle Paris 14:325-366.

C.R. McClain, personal communication