Essences and Anglerfish: Does Polymorphism Refute Thomistic Biological Essentialism?

Thomistic biological essentialism is faced with the problem of intraspecific variation. David Oderberg and Edward Feser offer a solution to this problem. I argue that Oderberg and Feser's proposed solution is insufficient because it cannot handle cases of polymorphic and polyphenic variation. Thomists, however, are not forced to abandon biological essentialism altogether. I offer a version of Thomistic biological essentialism, inspired by Charles De Koninck and Mortimer Adler, which can better accommodate polymorphic and polyphonic variation.