Diversity and functional significance of pigment in protozoa, porifera and cnidaria

Pigmentation in non-chordate animals is highly diverse and essential for survival, ecological interactions, and communication Protozoans, sponges (Porifera), and cnidarians display vivid coloration derived from various pigment types, distinct from the melanin-based systems in vertebrates. In protozoans, pigments like blepharismin and xanthophylls are synthesized endogenously or acquired from diet, serving roles in photosynthesis, light perception, antioxidant defense, and behavioral responses such as, phototaxis. Other pigments including staphyloxanthin melanin, and porphyrins-protect cells from oxidative stress and contribute to defense mechanisms In sponges, carotenoids produce orange, red, and yellow hues, while melanin adds darker tones, pigments from symbiotic algae, such as chlorophylls and phycoerythrins, further diversify coloration, sometimes forming pigment-protein complexes that result in unusual shades like blue or green. Cnidarians utilize carotenoids, melanins, and tetrapvroles for yellow orange, or brown coloration, with specialized pigments such as blue thizostomins providing UV protection and luciferins enabling bioluminescence. Many cnidarians also express green fluorescent proteins (GFPs) and their variants, which play roles in light absorption, signaling, and photoprotection. Together, these pigment systems underscore the biochemical versatility and adaptive importance of coloration across non-chordate lineages.