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.
Serpula
Like other annelids, these worms possess well-developed nervous systems. The nervous system consists of a central brain in the upper part of the head, which is relatively large compared with that of other annelids. Extending from the brain is a large ventral nerve cord running the length of the body. There are many supporting ganglia along the length of this cord (including pleural, pedal and cerebral ganglia), and a series of small nerves in each body segment. Signals transmitted through the pedal ganglia allow the worms to retract rapidly into their tube if threatened.