Table 1.

Forms of cellular excitability in eukaryotes are contrasted with those in prokaryotes. See main text for references.

forms of cellular excitability	prokaryotic examples	eukaryotic examples	made possible by
stochastic navigation	bacterial and archaeal chemotaxis, archaeal phototaxis	choanoflagellate aerotaxis, chemokinesis in some ciliates and flagellates, Micromonas phototaxis	any moving appendage or motility mechanism
spatial sensing	Synechocystis, Thioturbo danicus	amoebae, ciliates	spatially located sensor, large cell size
temporal taxes	Thiovulum	helical photo- and chemotaxis across eukaryotes	helical/chiral self-motion, fine motor control over cilia or flagella, temporal sensing, memory
cell fusion	some haloarchaea (incomplete), Borrelia (mostly OM, incomplete), Clostridium spp. (complete)	all gametic fusion events	cell–cell recognition, adhesion, in most eukaryotes mediated by cilia/flagella
active feeding by engulfment	some planctomycetes	many eukaryotic phagotrophs	deformable membrane, cell recognition, sometimes by specialized appendages, internal digestion
mechanosensitivity and flow interactions	osmosensation	many eukaryotes	mechanosensory channels (e.g. transient receptor potential), membrane fluidity
escape responses and action potentials	cable bacteria, some biofilms	many eukaryotes	voltage and calcium channels (e.g. Cav, Nav), often localized to cilia/flagella