Rapid physiological integration of fused ctenophores.

The mechanisms by which organisms recognize the 'self' from the 'non-self' remain poorly understood. Moreover, the capability of transplanted tissue to functionally integrate is unclear in many organisms. Here, we report that two injured Mnemiopsis leidyi individuals, a species of planktonic animals known as comb jellies or ctenophores, are capable of rapidly fusing into a single entity in which some physiological functions are integrated. Our results highlight two interesting phenomena. First, ctenophores may lack an allorecognition mechanism that prevents fusion events between conspecifics. Second, fused individuals rapidly integrate and share physiological functions and neurobehavioral outputs. Ctenophores are among the earliest-branching animal groups of extant metazoans and possess a unique nervous system with enigmatic homology to other phyla Our observations warrant further research into understanding the evolution of self-nonself recognition systems and the functional integration of neuronal structures in ctenophores.