The jellyfish genome sheds light on the early evolution of active predation

Unique among cnidarians, jellyfish have remarkable morphological and biochemical innovations that allow them to actively hunt in the water column. One of the first animals to become free-swimming, jellyfish employ pulsed jet propulsion and venomous tentacles to capture prey. To understand these key innovations, we sequenced the genome of the giant Nomura jellyfish (Nemopilema nomurai), and the transcriptomes of its medusa bell and tentacles and complemented it with transcriptomes across tissues and developmental stages of another jellyfish, Sanderia malayensis. Analyses of Nemopilema and other cnidarian genomes revealed adaptations associated with active swimming and mobile predation, marked by codon bias in muscle contraction and the expansion of neurotransmitter genes. Nemopilema also showed a conservation in cellular chemical homeostasis and ion transport function, probably reflecting the high demand for sodium ions created by their muscle contraction-based locomotion. We also discovered expanded myosin heavy and light chain genes, Wnt genes, posterior Hox genes, and venom domains, possibly contributing to jellyfish mobility, medusa structure formation, and active predation, respectively. Taken together, the jellyfish genome and transcriptomes genetically confirm their unique morphological and physiological traits that have combined to make these animals one of the worlds earliest and most successful multi-cellular predators.