A natural science oddity, the seahorse reverses normal animal kingdom roles by having the male gestate and give birth to the young. Today, these fragile fish are threatened by degradation of their coastal habitats and overfishing for traditional medicines. In Greek mythology, hippocampus refers to the equine-fish hybrids that drew the water chariot of Poseidon, god of the sea and earthquakes.The name was later used for a structure within the brain that is shaped like a seahorse. Humans and other mammals have two hippocampi, one in each of the temporal lobes. The hippocampal network plays an important role in storing long-term memories and regulating spatial navigation. Recent neuroscience studies suggest it also enables the flexible reconstruction and recombination of multivalent memory associations. This feature is thought to support flexible behaviour and thinking, including the creative capacity to imagine fictional or future scenarios. Penelope and the Seahorse multiplies flexible memory associations, combining natural history, myths, half-truths, and dreams, while spanning the deep time of a pagan past, modernity and future imaginings. Dwyer weaves ancient Greek mythologies into a futuristic vision of marine life as ghostly apparition.