Slit-like structures on the prosomal appendages of the eurypterid Baltoeurypterus
Jason A. Dunlop & Simon J. Braddy
Department of Earth Sciences University of Manchester, Manchester, M13 9PL, Großbritannien
Distinct notches in the cuticle are reported on the dorsal, distal margin of podomere 7 of prosomal limbs IV and V in the eurypterid (Chelicerata: Eurypterida) Baltoeurypterus tetragonophthalamus (Fischer 1839). These eurypterid structures resemble arachnid slit sensilla, but are an order of magnitude wider and marginal on the podomere compared to arachnid sensilla. If slit sensilla, or their precursors, are present in eurypterids, this draws into question using slit sensilla as an autapomorphy for Arachnida.
Neues Jahrbuch für Geologie und Paläontologie, Monatschefte, 1997 (1), 31-38 (1997)
Author's comments:
OK we can't prove we have slit-sensilla in a eurypterid, but they are something of a smoking gun and I really think it's significant that they are on the same podomere as in some early trigonotarbid arachnids.
So far 
people were interested in eurypterid slit-like structures