Persistent, internal associations between bacteria and blood-feeding marine annelids and crustaceans

Obligate blood-feeding invertebrates exist in the oceans, yet symbiotic associations between them and beneficial bacteria have not yet been explored, until now. In this study, persistent internal associations with bacteria were observed for 6 phylogenetically-diverse species of marine obligate blood-feeders, including leeches, isopods, and copepods. Stable low-diversity, bacterial communities, distinct from non-blood-feeding relatives, biological surfaces, and seawater, over 5 years of collection hints at intimate and non-random bacterial associations. The distinctiveness of their bacteria from those associated with the environment and other non-hematophagous animals, further suggests a specific, exclusive, and likely functional relationship.