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Roundworm

Caenorhabditis elegans

A worm about a millimetre long with exactly 302 neurons. It was the first animal to have its complete wiring diagram mapped.

Neurons

302 measured · whole nervous system (hermaphrodite)

White JG, Southgate E, Thomson JN, Brenner S (1986) The structure of the nervous system of the nematode Caenorhabditis elegans. Phil Trans R Soc Lond B 314(1165):1-340. doi:10.1098/rstb.1986.0056.

Evidence

• It shows habituation, associative learning and memory. Its full connectome is known (now updated for both sexes).
  Cook SJ, Jarrell TA, Brittin CA, Wang Y, et al. (2019) Whole-animal connectomes of both Caenorhabditis elegans sexes. Nature 571(7763):63-71. doi:10.1038/s41586-019-1352-7.
• A review of learning and memory in the worm.
  Ardiel EL, Rankin CH (2010). An elegant mind: learning and memory in C. elegans. Learn Mem 17:191-201. doi:10.1101/lm.960510.

Assess it against the published criteria