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 437 year old marine strata of Wisconsin. Lacking preserved internal organs, it is ∼16 cm long, 8.2 mm wide, with 250 annulations and a circular structure at one end, which the authors interpret as the broken end of a molt. It is therefore referred to the Cycloneuralia, a group of worms that shed their skin. 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.