A specimen of the Recent cidaroid echinoid Eucidaris tribuloides (Lamarck) from the seaward side of the Palisadoes, parish of St. Andrew, Jamaica, has an aberrant apical system, although the corona appears normal. It includes eleven plates, rather than ten, due to the presence of an intrusive periproctal? plate between ocular V and genital 5. Rather than five genital pores distributed evenly between the five genital plates, there are, abnormally, eleven genital pores: eight occur in genital plates (either singly or paired); two are shared between a genital plate and adjacent ocular plate; and, most curiously, one is shared between adjacent ocular and periproctal plates. Most probably this rare and complex growth deformity was driven by some parasitic or environmental interaction. It is at present impossible to determine if such deformities occurred in the Pleistocene. Although E. tribuloides has a good fossil record, it is most commonly identified from spines and the rare Pleistocene tests that are known invariably have lost the apical system before burial.