Selective behavioral response of Trichoplax (Placozoa) to RGB-light stimuli
Authors: Kaptsov Valery A. , Deynego Vitaly N. , Kozyritsky Daniil V. 
Published: February 2022

Introduction. The marine animal Trichoplax (Placozoa), which has the animalcular organization among invertebrates, but with outstanding social behaviour and specific movement of the body and its cells, is a model animal for studying various biophysical and chemical processes, including responses to external stimuli. In the articles of specialists from many universities, the problem of Trichoplax phototaxis (Placozoa) is covered in a hypothetical and declarative form. However, there are no specific studies on the behavioural response of these protozoa and their cells to monochrome light signals with different wavelengths that are characteristic of its light habitat at a depth of 5 to 20 meters. Materials and methods. The studies were conducted on laboratory animals Trichoplax sp. H2. Studies of the behavioural response of Trichoplax were performed using modern methods of optical microscopy: Nikon Eclipse Ts2R-Fl Optical Microscope; optical microscopes: Nikon SMZ-1270, Stemi 305; An optical microscope “Leonardo 3.0“(specially designed for the project) allows simultaneously observing the behaviour of a group of Trichoplax and each Trichoplax of this group at a low level of illumination and a stable temperature of its aquatic habitat. Two web cameras were used in the microscope-the upper one with a 1.9 Mp matrix and the lower one - 5 Mp). Results. The theoretical analysis of the spectral composition of light and the degree of its polarization in the marine habitat of the protozoan multicellular animal Trichoplax (Placozoa) and the features of its gene-cell structure is carried out. Based on the laws of hydrooptics and the survival strategy (“food-prey”), the coordinate axes of the light-medium for Trichoplax are determined (the light vertical (395 nm) and two horizontal light axes - the reflected horizontal light from the food (green - 532 nm) and the fluorescent light coming from the aragonite shell of the predator mollusc (red - 630 nm). Based on the animal’s responses to these RGB light stimuli, the hypothesis of RGB phototaxis in Trichoplax and the kinesis of its cells was expressed and confirmed. The monochrome light signals red - 630 nm, green - 532 nm and blue - 395 nm are selected for Trichoplax control. Limitations of the study. In the study of Trichoplax (Placozoa), the behavioural response of this animal and its cells to monochrome light signals with different wavelengths was studied using modern optical microscopy methods, which make it possible to simultaneously observe the behaviour of both the Trichoplax group and each animal of this group at a low level of illumination and stable temperature of its aquatic environment. Conclusion. For the first time, the behaviour of Trichoplax and its cells was controlled using light signals, and the presence of RGB phototaxis and kinesis in its cells was also proved in Trichoplax. The discovery of the RGB-taxis Trichoplax (Placozoa) changed the established scientific ideas in the evolution of colour vision in animals Trichoplax (Placozoa) and the human visual analyzer functioning of its pineal gland. The presented method can be used in hygienic studies of the influence of external pollutants on the environment and the effect of light on the human pineal gland.