The senses of sea anemones: responses of the SS1 nerve net to chemical and mechanical stimuli

Abstract

The ectodermal slow system (SS1)is one of 3 separate nerve nets in sea anemones. SS1 sensory responses coordinate swimming in Stomphia coccinea (escape response) and expansion to dissolved food substances in Urticina felina (pre-feeding response). Here we have studied Actinia equina, Anemonia viridis, and Anthopleura ballii. Although these anemones can escape from nudibranch predators, the SS1 response to attack by Aeolidia papillosa is probably evoked mechanically rather than chemically (cf. Stomphia). Multiple SS1 pulses to mechanical stimulation are described for the first time. Previous work has shown that in the pre-feeding response of Urticina the SS1 is excited by betaine; in Actinia however, the excitant is proline. The anemones studied can utilize the SS1 in 2 different behavioural responses (escape and pre-feeding/feeding) because the different receptors involved respond at different frequencies (at around 0.6 Hz in escape and 0.2 Hz in pre-feeding).