The book presents richly illustrated natural-history sketches of small aquatic animals, progressing from freshwater ponds, ditches and streams to coastal and oceanic habitats. Chapters examine major groups—crustaceans, mollusks, cnidarians, echinoderms, sponges and microscopic forms—outlining anatomy, behavior, feeding and reproductive habits, coloration and ecological roles. Descriptions emphasize the variety of forms and life strategies found in different water bodies and provide accessible, grouped accounts of notable species, supported by an alphabetical index for further reference.