Overview
Caenorhabditis elegans is a 1-millimeter nematode worm with a nervous system of exactly 302 neurons (hermaphrodite) and 385 (male). It is the only animal for which the complete synaptic wiring diagram — the connectome — has been fully determined. This makes it an unparalleled model organism for studying how neural circuits generate behavior.
The original wiring diagram was determined by Sydney Brenner's laboratory at the MRC Laboratory of Molecular Biology over the course of more than a decade, published in the landmark 1986 paper by White, Southgate, Thomson & Brenner. The data were digitized and curated by David Hall (Albert Einstein College of Medicine) and made available to the community.
The Open Connectome Project hosts both the hermaphrodite and male C. elegans connectome datasets, contributed by Scott Emmons (Albert Einstein College of Medicine) and David Hall. These datasets include chemical synapses, gap junctions (electrical synapses), and neuromuscular junctions, with connection weights derived from synapse size.
The C. elegans Nervous System
Hermaphrodite
Male
The hermaphrodite connectome is the classic reference dataset, first published by White et al. (1986) from MRC LMB Cambridge. It describes 282 somatic neurons and 20 pharyngeal neurons connected by approximately 2,990 chemical synapses, 890 gap junctions, and 1,410 neuromuscular junctions.
The male connectome — particularly the posterior nervous system — was mapped by the Emmons laboratory (Jarrell et al., Science 2012). Of the 170 posterior neurons studied, 144 participate in the mating behavior circuit, providing a direct link between connectome structure and behavior. A key innovation was including synapse size as a proxy for connection strength, revealing that interaction strengths vary more than 100-fold across the connectome.
History of the C. elegans Connectome
Accessing the Data
The C. elegans connectome data is freely available through the OCP infrastructure and partner resources. No account or registration required.
AWS Open Data
All OCP data including the C. elegans connectome is hosted on the AWS Open NeuroData Registry. Direct S3 access available.
WormWiring.org
The Emmons Lab hosts skeleton diagrams, synapse lists, and connectivity matrices at wormwiring.org — the primary reference for curated C. elegans wiring data.
OCP REST API
Programmatic access via our RESTful API. Query connectivity matrices, neuron metadata, synapse lists, and spatial annotation data. See API reference below.
Python / MATLAB
The C. elegans connectivity matrices are available as .csv, .mat, and .xls formats, readable by any standard toolchain.
CATMAID Viewer
Visualize neuron morphologies and connectivity directly in the browser via our CATMAID integration — no software installation required.
Connectome Toolbox
The C. elegans Connectome Toolbox (OpenWorm) provides structured datasets for chemical, electrical, and extrasynaptic connectivity across multiple reference publications.
API Reference
All OCP data services are available as stateless RESTful APIs. The C. elegans annotation project supports the full query interface:
→List all 302 hermaphrodite neurons with metadata
→Return all chemical synapses with pre/post identifiers and weights
→Return all gap junctions (electrical synapses)
→Return 144 mating circuit neurons from male posterior connectome
→Connectivity for neuron AVAL (pre + post + gap junctions + NMJs)
→Download full 302×302 weighted adjacency matrix as CSV
→Batch write annotations (neuron labels, curations, metadata)
Neuron ID Examples
AVAL
AVAR
AVBL
AVBR
AVDL
AVDR
AVEL
AVER
PVCL
PVCR
ASEL
ASER
AFD
AIY
AIZ
AWA
AWC
PHB
AVA
AVB
+ 282 more
Key Publications
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S. J. Cook, T. A. Jarrell, C. Brittin, Y. Wang, A. E. Bloniarz, M. A. Yakovlev, K. C. Q. Nguyen, L. T.-H. Tang, E. A. Bayer, J. S. Duerr, H. Bülow, O. Hobert, D. H. Hall, and S. W. Emmons. Whole-animal connectomes of both Caenorhabditis elegans sexes. Nature 571, 63–71, 2019.
Nature · 2019 -
T. A. Jarrell, Y. Wang, A. E. Bloniarz, C. A. Brittin, M. Xu, J. N. Thomson, D. G. Albertson, D. H. Hall, and S. W. Emmons. The connectome of a decision-making neural network. Science 337, 437–444, 2012. Awarded the 2012–2013 AAAS Newcomb Cleveland Prize.
Science · 2012 · AAAS Prize -
J. G. White, E. Southgate, J. N. Thomson, and S. Brenner. The structure of the nervous system of the nematode Caenorhabditis elegans. Philosophical Transactions of the Royal Society B 314, 1–340, 1986.
Phil. Trans. R. Soc. B · 1986 · Foundational Reference -
L. R. Varshney, B. L. Chen, E. Paniagua, D. H. Hall, and D. B. Chklovskii. Structural properties of the Caenorhabditis elegans neuronal network. PLOS Computational Biology 7(2), 2011.
PLOS Computational Biology · 2011 -
C. A. Brittin, S. J. Cook, D. H. Hall, S. W. Emmons, and N. Cohen. A multi-scale brain map derived from whole-brain volumetric reconstructions. Nature 591, 2021.
Nature · 2021