The book explores the evolutionary history and biological significance of two ancient and unique groups of invertebrates: horseshoe crabs and velvet worms. Richard A. Fortey, a renowned paleontologist and author, delves into the deep past to trace the lineage of these creatures, examining their remarkable adaptations and their place in the tree of life. The work likely investigates their fossil records, anatomical features, and ecological roles, offering insights into the broader processes of evolution and biodiversity.

Richard A. Fortey's work is generally well-regarded for its authoritative yet accessible approach to natural history subjects. His previous books have been praised for their depth of knowledge and engaging prose, suggesting this exploration of horseshoe crabs and velvet worms will similarly appeal to readers interested in evolutionary biology and zoology. The book likely offers a comprehensive overview of these fascinating creatures, drawing on extensive scientific research to illuminate their ancient origins and unique biological characteristics. It is expected to be a valuable resource for both general readers and those with a specific interest in invertebrate paleontology and zoology.