Instead, this cell type might represent an evolutionary precursor to a true nervous system, says Jacob Musser, an evolutionary biologist at EMBL, who co-authored the study. However, these neuroid cells are not nerves, and there is no sign of the synapses that enable neurons to communicate so quickly. On the basis of the proximity of the two cell types and the expression of genes that might allow for the secretion of chemicals, the researchers think that these arms enable neuroids to communicate with choanocytes, so that they can pause the water-flow system and clear out any debris or foreign microbes. The scans revealed that neuroids send out long arms to reach choanocytes, a type of cell with hair-like protrusions that drive sponges’ water-flow systems and capture most of their food. The researchers then used X-ray imaging and electron microscopy to study one of these cell types, which they called secretory neuroid cells. This suggests that some form of cellular communication might coordinate the animal’s filter-feeding behaviour.

Synaptic genes were active in a few of these types, which were clustered around the sponges’ digestive chambers. They found that the sponge has 18 distinct cell types.

To discover which cells were expressing these genes, Detlev Arendt, an evolutionary biologist at the European Molecular Biology Laboratory (EMBL) in Heidelberg, Germany, and colleagues sequenced the RNA in various individual cells from a freshwater sponge ( Spongilla lacustris). Previous research has found that sponges possess genes encoding proteins that typically help synapses to function, despite the animals’ lack of neurons.

“This is a really exciting study that allows us to see sponges in a new light,” he says.Ĭells frequently communicate with one another, and neurons do so by passing electrical or chemical signals through tiny, targeted connections called synapses. The findings could help to understand how animals’ nervous systems evolved, says Casey Dunn, an evolutionary biologist at Yale University in New Haven, Connecticut, who studies marine invertebrates.

Their mastery of this complex behaviour is all the more remarkable because they have no brain, nor even a single neuron to their name.Ī study published on 4 November in Science now reveals that sponges use an intricate cell communication system to regulate their feeding and to potentially weed out invading bacteria. Sponges are simple creatures, yet they are expert filter feeders, straining tens of thousands of litres of water through their bodies every day to collect their food.

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