Non-invasive in vivo spectroscopy using a monitor calibrator: A case of planarian feeding and digestion statuses

• A monitor calibrator has been applied for non-invasive in vivo spectral measurements. • A simple measurement technique without the need of specialized cuvettes was proposed. • A monitor calibrator enabled quantitative tracking a planarian digestion dynamics. • It was possible to discriminate planaria by their state depending on the type of food. A mini-spectrophotometer monitor calibrator has been applied for non-invasive in vivo measurements of hemolymph spectra of invertebrate animals in the visible range. Planaria ( Girardia tigrina ) were used as test organisms, which were hungry or fed with mosquito larvae or beetle pupae. Spectral measurements of planarian’s hemolymph were made directly on a white scattering screen for the animals of various size and satiety during the food digestion. Features of both absolute and normalized spectra were analyzed. Using characteristic bands in the normalized spectra, criteria for estimation of satiety degree have been proposed that enable both tracking the digestion dynamics and discriminating planaria by their state. These criteria are based on absorbance rates at 430 to 540 nm for feeding with beetle pupae, and at 540 to 640 nm for feeding with mosquito larvae. The discrimination of planaria could be made with reliability at least of about 80% even for organisms of different size. We suggest that the easy control of planarian feeding status and their digestion dynamics using a monitor calibrator is promising for ecological and toxicological monitoring of their habitation areas and media.