A neurophylogenetic approach provides new insight to the evolution of Scaphopoda.
The position of scaphopods in molluscan phylogeny remains singularly contentious, with several sister relationships supported by morphological and phylogenomic data: Scaphopoda + Bivalvia (Diasoma), Scaphopoda + Cephalopoda (Variopoda), and Scaphopoda + Gastropoda. Nervous system architecture has contributed significant insights to reconstructing phylogeny in the Mollusca and other invertebrate groups, but a modern neurophylogenetic approach has not been applied to molluscs, hampered by a lack of clearly defined homologous characters that can be unequivocally compared across the radical body plan disparity among the living clades. We present the first three-dimensional reconstruction of the anterior nervous system of a scaphopod, Rhabdus rectius, using histological tomography. We also describe a new putative sensory organ, a paired and pigmented sensory mantle slit. This structure is restricted to our study species and not a general feature of scaphopods, but it forms an integral part of the description of the nervous system in R. rectius. It also highlights the potential utility of neuro-anatomical characters for multiple levels of phylogenetic inference beyond this study. This potential has not previously been exploited for the thorny problem of molluscan phylogeny. The neuroanatomy of scaphopods demonstrates a highly derived architecture that shares a number of key characters with the cephalopod nervous system, and supports a Scaphopoda + Cephalopoda grouping.
School of Biological Sciences, Queen's University Belfast, Northern Ireland.|Queen's University Marine Laboratory, Queen's University Belfast, Northern Ireland.
Lauren H
LH
Sumner-Rooney
SNSB-Zoologische Staatssammlung M, ü, nchen, Germany.|Biozentrum, Ludwig-Maximilians-Universität München, Germany.
Michael
M
Schrödl
SNSB-Zoologische Staatssammlung M, ü, nchen, Germany.
Eva
E
Lodde-Bensch
Department of Integrative Biology and Museum of Palaeontology, University of California, Berkeley, CA, USA.
David R
DR
Lindberg
Biozentrum, Ludwig-Maximilians-Universität München, Germany.
Martin
M
Heß
School of Biological Sciences, Queen's University Belfast, Northern Ireland.
Gerard P
GP
Brennan
School of Biological Sciences, Queen's University Belfast, Northern Ireland.|Queen's University Marine Laboratory, Queen's University Belfast, Northern Ireland.
Julia D
JD
Sigwart
D000818:Animals; D005075:Biological Evolution; D008974:Mollusca / Q000033:anatomy & histology* / Q000145:classification; D009420:Nervous System / Q000033:anatomy & histology; D010802:Phylogeny