The first three slides present Beu’s analysis, descriptions and conclusions in his 2010 paper.  Page numbers annotated in the slides refer to this paper. Overall Beu relied upon analysis of morphological characters of specimens in the “complex” throughout its worldwide distribution.  He relied upon examination of published material and specimens from museum and private collections.  Beu concluded that the “complex” consisted of several possible forms of one species; namely, Monoplex pilearis, and that Monoplex martinianus was one of the forms, but that Monoplex aquatilis “is easily distinguished from all the other members of the group.”  The “complex” consisted of Monoplex pilearis, Monoplex martinianus plus other forms that might one day be distinguished.  He conclude that “only molecular analysis will clarify its status.”  Despite his comment that Monoplex aquatilis was “easily distinguished” from the Monoplex pilearis complex, I also feel “only molecular analysis will clarify its status.”   However, I rely heavily on protoconchs in separating species and the protoconchs of M. pilearis and M. aquatilis are clearly different (see slide 12).  Unfortunately, these species are most often decollated.  My focus is limited to those shells found in the western Atlantic, which are acknowledged to display similar, but often consistent variations in characters than shells in the Indian and Pacific oceans. I’ve found in the western Atlantic specimens that, if the protoconchs are absent, then the colors of the apertures (esp. the columella) are the only “consistent” characters to distinguish M. aquatilis and M. pilearis.  All other characters are too variable, and the variations occur in both species.

As of August 2024, WoRMS treats Monoplex martinianus as a synonym of Monoplex pilearis and treats Monoplex aquatilis as an “accepted” species based upon Beu’s 2010 paper.