A new species of Microeledone from Galápagos Islands and an amended diagnosis of the Megaleledonidae (Octopoda: Incirrata).

The octopod fauna of the deep tropical Pacific Ocean remains poorly known, as is the octopod family Megaleledonidae Taki. A single female megaleledonid specimen collected at 1773 m depth near the equatorial Galápagos island of Darwin is named Microeledone galapagensis sp. nov. This small, squat, short-armed octopod has few arm suckers and gill lamellae. Its lack of a crop diverticulum, ink sac, and anal flaps suggests that it pertains to Thaumeledone. However, its smooth skin, which dorsally is nearly free of pigment, large rachidian tooth, and large funnel organ ally it with the monotypic Microeledone. Its reverse countershading and dense pigmentation on the inner dorsal mantle musculature distinguish this species from Microeledone mangoldi Norman, Hochberg & Boucher-Rodoni, 2004a. This species belies the definition of the Megaleledonidae as large-bodied, Southern Ocean endemics, leading us to revise the family diagnosis. The short arms carrying few suckers in this genus and Thaumeledone are hypothesized to relate to heterochrony, potentially increasing energy available for reproduction and contributing to niche partitioning.