Terrigenous leaf-utilizing life of the tube-bearing annelid Anchinothria cirrobranchiata (Annelida: Onuphidae) in the deep sea

Deep-sea ecosystems are generally oligotrophic because they lack photosynthesizing producers. On deep-sea slopes near land, however, various terrestrial plant remains flow to and are deposited on near-shore deep bottoms. From a depth of 300 m off the Pacific coast of Owase, central Japan, we collected an onuphid polychaete, Anchinothria cirrobranchiata (Annelida: Onuphidae), which lives in a dorsoventrally flattened portable tube. The polychaete tubes were made of sand, as well as leaves and twigs of terrestrial evergreen trees. The leaves glued on the portable tubes were chartaceous, blackish and tough; they belonged mainly to two genera of Fagaceae, Castanopsis and Quercus, which are dominant components of coastal evergreen oak forests. In aquaria, the polychaetes fed on the leaves on their tubes, as well as autochthonous sedimented leaves, suggesting utilization of terrigenous plant litter as food. As to the evolution of Anchinothria, a molecular phylogenetic analysis suggests that Anchinothria is monophyletic with other Hyalinoeciinae (Nothria, Leptoecia, Hyalinoecia).