Oichnus simplex Bromley infesting Hemipneustes striatoradiatus (Leske) (Echinoidea) from the Maastrichtian type area (Upper Cretaceous, The Netherlands)

The large holasteroid echinoid Hemipneustes striatoradiatus (Leske) was exploited by diverse invertebrate encrusters and borers during the Maastrichtian, both pre- and post-mortem. In life, the specimen described herein was perforated by multiple Oichnus simplex Bromley borings close to the apical system. Each engendered a growth reaction from the echinoid, a mound-like swelling on the external surface of the test with the boring at the centre. These would have been moved away from the apical system as the echinoid grew and inserted new plates apically. Whether this infestation was the product of numerous individual organisms or, less likely, just one organism (gastropod?) that relocated when discouraged by each mound-like swelling is uncertain. Similar growth reactions are known from other echinoderms, but associated with non-penetrative Oichnus paraboloides Bromley.