Meeting Abstract

27.3  Monday, Jan. 5  Fantastic pelagic diversity within Acrocirridae (Polychaeta) OSBORN, K. J.*; ROUSE, G. W.; Scripps Institution of Oceanography, UCSD; Scripps Institution of Oceanography, UCSD kjosborn@ucsd.edu

At least seven new species of large, swimming polychaetes were collected while exploring the deep water-column with remotely operated vehicles since 2001. Deep bentho-pelagic animals are historically understudied due to their ability to escape benthic trawls, the difficulties of towing pelagic nets near the seafloor at great depths, and the fragility of many of these species. Animals from this habitat are of particular interest because they often possess unique morphological and ecological adaptations in comparison to their benthic relatives. The recently discovered worms belong to the polychaete family Acrocirridae, a group previously consisting of small, generally narrow-bodied worms with few chaetae. The new worms form a monophyletic clade with four distinct subclades and seven species. All are pelagic or bentho-pelagic, possess fantastic features (i.e. novel bioluminescent apparati, elongate branchiae, and complex sensory organs), and exhibit morphological adaptations assumed to be associated with their use of the water-column (i.e. numerous elongate, sometimes paddle-like chaetae and a thick gelatinous sheath). Phylogenetic relationships were reconstructed based on five genetic markers and morphological characters mapped on the resulting tree in order to assess character transitions. The discovery of this group strongly supports the assertion that continued exploration of the deep sea is necessary, as well as has broad implications for our understanding of evolution of pelagicism. Specifically, this project sheds light on the evolutionary history of the cirratuliform polychaetes and focuses on the morphological transformations observed during the transition from benthic to pelagic living.