Entities › Animals and other organisms › Nerve nets, no brain

Hydra

Hydra vulgaris

A small freshwater cnidarian. It's controlled by a diffuse nerve net and has no brain.

Neurons

about 3,000 to 5,000 estimate · whole nerve net; no exact count exists

Bode H, Berking S, David CN, Gierer A, Schaller H, Trenkner E (1973) Quantitative analysis of cell types during growth and morphogenesis in Hydra. Wilhelm Roux Arch Entwickl Mech Org 171(4):269-285. doi:10.1007/BF00577725.

Evidence

• Its behaviour (contracting, feeding, somersaulting) is driven by a nerve net with no brain. Calcium imaging of the whole animal has mapped its groups of neurons.
  Dupre C, Yuste R (2017) Non-overlapping neural networks in Hydra vulgaris. Curr Biol 27(8):1085-1097. doi:10.1016/j.cub.2017.02.049.

Assess it against the published criteria