Not the first leech: An unusual worm from the early Silurian of Wisconsin.

An unusual worm, previously interpreted as the earliest leech, is described from the early Silurian (Llandovery, Telychian) Brandon Bridge Formation Lagerstätte (Waukesha Biota) of Wisconsin (~437 Ma). Lacking preserved internal organs, it is up to ~16 cm long, 8.2 mm wide, with ~250 annulations and a circular structure at one end, interpreted here as the broken end of a molt. It is therefore referred to Cycloneuralia incertae sedis. [ABSTRACT FROM AUTHOR]