Cross references: Early Behavior Bilateria Bilateria Locomotion
Hemichordates Protochordates Chordates Chordate Locomotion
Amphioxus Locomotion Lamprey Locomotion
Single-Celled Ancient Ancestors
It's clear that the prokaryotes are able to move around as individuals. This would seem to be an early form of behavior.
"The complex life cycle of Myxococcus xanthus includes predation, swarming, fruiting-body formation and sporulation."
Quorum sensing allows groups of prokaryotes to synchronize their behavior and act as a temporary multicellular animal. Since the swarm moves through its environment as a unit, this is clearly a form of behavior on the multicellular level.
There are so many different kinds of eukaryotes that it's difficult to generalize about them. Although I haven't looked closely at many of them, I'm sure that they exhibit at least as much individual mobility as the prokaryotes, and I'm quite comfortable seeing this as a form of behavior.
"The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals." "The Volvocaceae are a family of unicellular or colonial biflagellates" The colonies seem quite mobile, and I don't see any reason to not refer to this as behavior.
"However, when food runs out, the amoebae send out chemical signals to surrounding amoebae. Next, they stream toward a central point and form a sluglike multicellular pseudoplasmodium, which can then migrate like a single organism." Clearly a form of behavior.
Multi-Celled Ancient Ancestors
"The only surviving parazoans are the sponges, which belong to the phylum Porifera, and one surviving species (Trichoplax adhaerens) in the phylum Placozoa."
"They have three cellular layers: ... the bottom layer is made up of cylinder cells which possess cilia used in locomotion"
Clearly an early form of behavior. Note the use of cillia.
"Despite the fact, that sponges do not posses muscles and a nervous system, they are able to react upon external stimuli [5-7], to move [7-10], to contract [summarised in 7], and display diurnal rhythms [7,11]."
"Active locomotion by individual marine and freshwater sponges across glass, plastic and rubber substrata has been studied in relation to the behavior of the sponges' component cells.
Sequential tracing of sponge outlines on aquarium walls shows that sponges can crawl up to 160 microns/hr (4 mm/day)."
"Our observations suggest that the displacement of sponges is achieved by the cumulative crawling locomotion of the cells that compose the sponge's lower surface."