The Hyperbolic Crochet Coral Reef (HCCR) is a distributed venture of thousands of women who cooperatively fabricate a collection of yarn and plastic coral reefs. Under the auspices of the Institute For Figuring, these crafters use the technique of “hyperbolic crochet” invented by geometer Daina Taimina to make wooly reefs, with the aim of drawing attention to the menace that climate change poses to the world’s coral reefs. Hyperbolic crochet is a method of fabricating models of hyperbolic geometry, a kind of non-Euclidean geometric space characterized by negative curvature. Many marine organisms have evolved to embody hyperbolic geometry; it affords them a maximum surface area with which to filter feed in a minimal volume. This essay asks, What is the place of biology—and specifically of biological theory—in the HCCR? After describing the Reef’s origins in geometrical modeling, the author traces the manifold biological theories that inform Reef makers’ descriptions of their project, showing how they gather and weave together the diverse theories and narratives that have marked nineteenth- and twentieth-century biology, drawing on contemporary, historic, and folk understandings of evolution and morphogenesis in describing their work. Such theories include Romantic notions of life forwarded by Johann Friedrich Goethe and Lorenz Oken, twentieth-century theoreticians such as D’Arcy Thompson and François Jacob, and, more recently, Susan Oyama and Niles Eldredge. The result is a composite, materially instantiated theory of biological change that is wholly their own.