Dumbo octopod hatchling provides insight into early cirrate life cycle

Summary Cirrate octopods (Cephalopoda: Cirrata) are among the largest invertebrates of the deep sea. These organisms have long been known to lay single, large egg capsules on hard substrates on the ocean bottom [1], including cold-water octocorals (Anthozoa: Octocorallia). The egg capsule is comprised of an external egg case as well as the chorion and developing embryo. Development in cirrates proceeds for an extended time without parental care [2]. Although juveniles have previously been collected in the midwater [3], cirrate hatchlings have so far never been observed. Here, we provide the first video of a living hatchling and use magnetic resonance imaging (MRI) to analyze its anatomy and assign the specimen to the genus Grimpoteuthis, the so-called dumbo octopods. The specimen's behavior and advanced state of organ development show that cirrate hatchlings possess all morphological features required for movement via fin-swimming, for visually and chemically sensing their environment, and for prey capture. In addition, the presence of a large internal yolk sac reduces the risk of failure at first feeding. These data provide evidence that dumbo octopods hatch as competent juveniles.