AN EXCEPTIONAL ASSEMBLAGE OF MACCOYA SPHAERICA (ECHINOIDEA) FROM THE MISSISSIPPIAN OF HOOK HEAD, CO. WEXFORD, IRELAND

Echinoids are seldom prominent or conspicuous elements of Paleozoic marine commu-nities. This could be a taphonomic artefact due to their flexible tests deflating and rapidly disarticulating after death—a fact that has undeniably hampered greater understanding of the group. Here, an extremely well-preserved cluster of echinoids is described from Tournaisian marine strata at Hook Head in southeast Ireland. All were collected in close proximity to each other and from essentially the same horizon towards the top of the Hook Head Formation, and all can be assigned to Maccoya sphaerica (M‘Coy, 1844) based on their interambulacral plating. Preservation of features on some specimens is so exceptional that they reveal hitherto unknown details about the peristome and adoral plating in the broader palaechinid group. The sedimentological setting of the fossil-bearing site at Hook Head is in deep water and well below wave base towards the distal end of a mixed silici-clastic-carbonate ramp. Conditions on the seafloor appear to have been very calm and quiet, with minimal post-mortem disturbance of the echinoids promoting their excellent preservation. It remains unclear why these specimens of M. sphaerica congregated in this particular location on the seafloor, or what ultimately led to their sudden demise.