Eusociality, the apex of animal social organization is distinguished by: (i) overlapping generations, (ii) reproductive division of labor, (iii) cooperative care of young, and (iv) defense of the colony or nest. Until very recently, eusociality appeared limited to terrestrial environments, recognized only among social insects (bees and wasps) and African naked mole-rats. Recent discoveries by the PI and colleagues have documented examples of this in marine ecosystems including a select group of snapping shrimps living in sponges and a single family of amphipod crustaceans living in sponges and sea squirts. This was a stunning finding, for it was thought that marine species did not exhibit this highly sophisticated level of social organization. Thomas first postulated eusocial structure in Leucothoid amphipods in the 1990's and has continued to describe new species and behavior in the highly derived tropical family where eusociality has been documented. However, a major conundrum remains to date as there are no "bridging" or intermediate representatives (semi-social, quasi-social, etc) within the Amphipoda, a feature common to all other examples of eusocial colonies discovered so far. Our research project targets an intermediate link (Paraleucothoe) in the continuum from extended parental care (Leucothoe) to true eusocial structure (Anamixis & Paranamixis). This species is found only in southern hemisphere marine environments from New Zealand to South Australia. To date, there is no live documentation of eusocial behavior, or transitional cues in Leucothoe. Thus, the study at hand would provide ground-breaking visual data for evolutionary biologists and ecologists alike. Our project requests support for the PI and two NSU students to travel to the Leigh Marine Lab in Auckland, New Zealand to study this remarkable evolutionary condition. As in past efforts by the PI student research will be full author level participants in this project.