The genus Diopatra is a major driver in sedimentary systems, altering the structure of habitats and changing the frequency of refugia and predator access to prey. It is taken as prey by a variety of shorebirds, crustaceans, and fish and used worldwide as bait. Diopatra are quite charismatic, with iridescent colour patterns and a willingness to be fed by hand by entranced biologists, and their larvae can only be described as 'cute'. One might expect then that given their importance to sedimentary systems, the bait trade, etc. that we would know more than we do about their reproductive modes, physiological tolerances, etc. than we do. The recent discovery that the predominant onuphid of the very well-known Atlantic coast of Europe, D. neapolitana, is a protandric sequential hermaphrodite is startling. This special volume dedicated to Diopatra will hopefully stimulate more investigations and further insights. The annelid genus Diopatra occurs in all major oceans but is best represented in the shallow depths of warmer waters, where it lives in elaborately decorated tubes. This paper provides an introduction to the animals, discussing their history and diversity. We describe and illustrate its morphology and geographic distribution. While they were thought to be predominantly gonochoristic, recent reproductive studies show that several species are protandric simultaneous hermaphrodites. Development is by broadcast spawning with a brief pelagic stage or direct development in the parental tube or egg mass attached to it. Diopatra is a key ecosystem engineer, altering water flow and deposition and increasing the availability of refugia. We also discuss its harvesting as fishing bait, its role as an alien or introduced species, its capacity to regenerate, its therapeutic potential, and its applications as a bioindicator species for climate change, geographic distribution changes, and dispersal.
