Ontogeny is the study of the developmental history of an organism. Here, one must consider all the stages that make up an animal’s biological life, from the fertilized egg to its most mature form. Ontogeny is said to “recapitulate” phylogeny, acting as a small-scale, individualized rendition of the evolutionary process. Rather, just as life itself has come to grow, develop, and complexify over time, so does the unfolding of every solitary organism. As individuals must then be contextualized, ontogeny also examines the influence of an animal’s environment, and how the greater “gestalt” of this interaction between internal and external conditions comes to determine their behavior.

With regards to the question of transdifferentiation, however, this notion is altogether challenged; T. nutricula do not progress through such a successive series of life stages, but instead exhibit a sort of reverse-ontogeny (Piraino, et al. 1996), reacting to changes in its environment, directing and re-directing its biological sequence accordingly. Whereas sexual maturity typically denotes the end of an organism’s ontogenetic development (Stearns 1992), T. nutricula continues to transcend the boundaries of mortal degeneration.



The two general life stages of a Turritopsis nutricula: a medusa (L) and a polyp (R) (Ker Than, 2009).

Although rife with subtleties and, of course, the usual biological exceptions, the hydrozoan life cycle is largely reducible to two basic stages: an asexual, larval, polyp stage, fully manifested through a colonial form, and a sexually-producing, adult, medusae stage, solitary and pelagic (Aerne, 1996). Eggs are fertilized as free-floating columns of sperm – released by male medusae – come into contact with female counterparts. As these stolons then break away from their mother medusae, they fall to an appropriate ocean surface, upon which they transform into polyps, eventually generating entire colonies. Each polyp can then bud and detach from its colony, so as to become a pelagic medusa (Hongbao Ma, 2010). The medusae themselves have an entirely different cellular structure than the polyp stage (Tardent 1978; Aerne, 1996). Despite this, transdifferentiation allow for medusae to revert back into polyps, regenerate entire colonies, and again resume in producing more medusae (Aerne, 1996).



The usual pathways of the Cnidarian life cycle are bypassed via transdifferentiation (Miglietta & Lessios, 2009).

But at one point during this life cycle does the ability to transdifferentiate first arrive? Aerne (1996) claims that when T. nutricula first enter the medusa stage, budding from polyps, the proper mechanisms are first formed. A polyp by itself would thus not be capable of regeneration whatsoever. Just the same, Bavestrello, et al. (1992) noted that there appeared to be no limit on medusae in regenerative powers. Piraino, et al. (1996) reaffirmed this claim, stating that all medusae of T. nutricula are capable of reversing the life cycle at any point.

Could the T. nutricula polyp thus undergo a sort of cellular “learning” when it first transforms into a medusa?