Comb Jellies Have Weird Nervous System

No other animal has a nervous system like a comb jelly, which suggests that they are in a very basal position in the animal kingdom's evolution.

Shimmering, gelatinous comb jellies wouldn’t appear to have much to hide. But their mostly see-through bodies cloak a nervous system unlike that of any other known animal, researchers report in the April 21 Science.

In the nervous systems of everything from anemones to aardvarks, electrical impulses pass between nerve cells, allowing for signals to move from one cell to the next. But the ctenophores’ cobweb of neurons, called a nerve net, is missing these distinct connection spots, or synapses. Instead, the nerve net is fused together, with long, stringy neurons sharing a cell membrane, a new 3-D map of its structure shows.

From Science News citing P. Burkhardt et al., "Syncytial nerve net in a ctenophore adds insights on the evolution of nervous systems" 380 Science 293 (April 21, 2023). doi: 10.1126/science.ade5645 

and 

A. Sebé-Pedrós et al., "Early metazoan cell type diversity and the evolution of multicellular gene regulation" Nature Ecology & Evolution (June 25, 2018) (published online) doi: 10.1038/s41559-018-0575-6