GABA and glycine modulate feeding cycles in Trichoplax adhaerens. (A) After adding 0.3 mM glycine, the number, and frequency of feeding cycles on green algae biofilm reduced approximately threefold compared to the control. (B) The effect of glycine on feeding activity is dose-dependent. 0.1 mM reduces the number of feeding cycles by 26%, 0.3 mM—by 86%. Asterisks denote a significant difference in feeding activity from the control (Welch t-test, *p < 0.05, ***p < 0.001). N animals = 65, 36, 29. (C) After 20 h in 1 mM GABA (C, right), the number and frequency of feeding cycles reduced approximately threefold compared to the control [after 20 h in pure artificial seawater (ASW)] (C, left). In control, Trichoplax exhibit feeding cycles every 10–15 min. (D) GABA decreased feeding activity on green algae and cyanobacterial biofilms in concentrations of 0.3 and 1 mM. Asterisks denote a significant difference in feeding activity from the control (Welch t-test, *p < 0.05, **p < 0.01, ***p < 0.001). N animals = 80, 64, 27, 26, 47, 40. (E) After adding 0.3 mM GABA, feeding activity decreased on the green algal mat (T. marina) after 1–2 h from the starting point and recovered after 11–12 h of incubation. N animals = 10.