Phylum Hemichordata (Peanut Worms)

Wikipedia Entry

Approximate Number of Species: 85

Largest: The largest colony is Cephalodiscus densus with a length of  8.2 feet (2.5 meters) and the noncolonial species is Balanoglossus gigas with a length of 9.8 inches (250 mm)

Smallest:  The smallest colony is the species Rhabdopleura compacta at 0.11 inches in diameter (2.9 mm ) and the smallest noncolonial species is Saccoglossus pygmaeus with a length of 0.12 inches (3 mm)

References:

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

Lambert G (2005) Ecology and natural history of the protochordates. Canadian Journal of Zoology 83:1-17.

Mierzejewski P & Kulicki C (2003) Cortical fibrils and secondary deposits in the periderm of the hemichordate Radbdopleura (Graptolithoidea). Acta Palaeontologica Polonica 48:99-111.