A new specimen of Paleomerus hamiltoni (Arthropoda

ABSTRACT: A fourth specimen of the enigmatic Lower Cambrian arthropod Paleomerus hamiltoni is described from the Mickwitzia Sandstone of Sweden. The nature of the telson of P. hamiltoni was previously unknown and it has been assumed that the abdomen consisted of 12 segments, the posterior-most being elongate and tapering. This new material constitutes a mould of the entire animal and a cast of the posterior-most abdominal segment and telson, proving that the abdomen consists of 11 segments and a short, tapering telson, which was previously misinterpreted as the twelfth abdominal segment. The presence of 11 abdominal segments in P. hamiltoni eliminates significant differences between it and Strabops thacheri, supporting assignment to Strabopidae and rendering the family Paleomeridae redundant. KEY WORDS: Atdabanian, Cambrian, Strabopidae, telson. Paleomerus hamiltoni is one of the oldest known arthropods. It was used as an outgroup by Dunlop & Selden (1997) and Anderson & Selden (1997) in their phylogenetic analysis of early chelicerates. As such, it may occupy an important position between stem-group chelicerates and other arachno