Sponge
Like cnidarians (jellyfish, etc.) and ctenophores (comb jellies), and unlike all other known metazoans, sponges' bodies consist of a non-living jelly-like mass (mesoglea) sandwiched between two main layers of cells. Cnidarians and ctenophores have simple nervous systems, and their cell layers are bound by internal connections and by being mounted on a basement membrane (thin fibrous mat, also known as "basal lamina"). Sponges have no nervous systems, their middle jelly-like layers have large and varied populations of cells, and some types of cells in their outer layers may move into the middle layer and change their functions.
Aglantha digitale
"Aglantha digitale" is unique among known jellyfish in having giant axons in the subumbrella (the concave inner surface of the bell) which are involved in a rapid escape response. Normally the hydrozoan swims by slowly pulsating its bell, movements produced by muscle contractions which eject water through the velar opening. However, when the animal is stimulated by manipulating the bell margin, or by squeezing or tugging a marginal tentacle, it responds very rapidly, producing up to three vigorous contractions that propel it a distance of about five body lengths. In its pelagic habitat, this hydrozoan finds itself among relatively fast moving crustaceans, fish larvae and arrow worms in a jostling diurnal vertical migration, and the escape response may help it to avoid damage to its fragile tissues. Observations from submersible craft have shown the hydrozoan behaving in this way.