---
title: "Hydra · Animals and other organisms · Entities · Simulation Hypothesis"
url: https://simulation-hypothesis.com/entities/hydra
description: "A small freshwater cnidarian. It's controlled by a diffuse nerve net and has no brain."
license: https://creativecommons.org/licenses/by/4.0/
credit: "Ross Allan Dahl, Simulation Hypothesis (simulation-hypothesis.com)"
---

[Entities](https://simulation-hypothesis.com/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