Fig. 4. Morphotypes of drill holes observed on tests of Echinocyamus linearis. A–F. Circular drill holes. A. Circular drill hole on MWG/ZI/022. B. Circular drill hole on MWG/ZI/005 in view perpendicular to the test surface (B1) and its close up in slightly oblique view (B2). Note that the walls of the drill hole are perpendicular to the test surface. C. Circular (subcircular) drill hole on MWG/ZI/023. D. Circular drill hole on oral side of MWG/ZI/024; d, drill hole; ps, peristom; pp, periproct. E. Circular (subcircular) drill hole on MWG/ZI/025. F. Circular (subcircular) drill hole on MWG/ZI/026. G. Drill hole transitional in outline circular (subcircular)/irregular on MWG/ZI/027. H, I. Complex drill holes on MWG/ZI/028 (H1) and MWG/ZI/29 (I1) with explanatory drawings (H2 and I2); c, circular part of drill hole; i, irregular part of drill hole. J–P. Irregular drill holes. J. Irregular drill hole on MWG/ZI/030. K. Irregular drill hole on MWG/ZI/031. Note three radial crevices running from the drill hole margin. L. Irregular drill hole on MWG/ZI/032. Drill hole outline slightly modified due to the occurrence of ambulacral pore. M. Irregular drill hole? on MWG/ZI/033. The upper part of drill hole appears to be partially defined by series of ambulacral pores. N. Irregular drill hole on MWG/ZI/008. Drill hole margin apparently defined by the plate margins. O. Large irregular drill hole on aboral side of MWG/ZI/034. P. Irregular drill hole on MWG/ZI/035. Drill hole outline strongly modified due to the occurrence of ambulacral pores. All specimens collected from coarse−grained Heterostegina Sands. Scale bars 0.2 mm.