The Ancient Language of Chemicals
In the silent, flowing world of freshwater habitats, a seemingly simple organism is performing a remarkable feat of coordination without a single neuron or muscle.
Sponges, or Porifera to scientists, have been thriving in Earth's waters for over 600 million years. These ancient animals lack the complex digestive, respiratory, circulatory, and nervous systems that characterize most other members of the animal kingdom 3 . Instead, their body plan is elegantly simple: a system of canals and chambers designed to filter microscopic food particles from water.
The architecture is basic but effective. Water enters through small pores called ostia, passes through channels where specialized collar cells capture food, and exits through larger openings called oscula 3 . This constant flow provides not only nourishment but also oxygen and waste removal, all accomplished through the simple power of diffusion.
Water flow through sponge anatomy showing entry (ostia) and exit (oscula) points
For decades, scientists have been fascinated by how sponges coordinate their behavior without the neural networks that nearly all other animals rely on. In creatures with nervous systems, communication is typically rapid: electrical impulses travel along nerve cells in milliseconds, enabling swift responses to the environment.
Sponge communication is different—more measured, more chemical, yet surprisingly effective. Their contractions are "rhythmic and in response to specific mechanical and chemical stimuli," but the timing depends on sponge size, ranging from about 40 minutes for tiny sponges to several days for larger specimens 6 .
The slow, deliberate pace of sponge behavior reflects a different approach to biological coordination, one that might represent an early evolutionary foray into cell-to-cell communication before the development of true nervous systems.
~40 minutes
Several hours
Several days
In 2025, a team of researchers tackled this mystery head-on using the freshwater sponge Ephydatia muelleri as their model. Their groundbreaking study, published in the Journal of Experimental Biology, set out to test whether ATP and glutamate—common signaling molecules in nervous systems—might play a role in coordinating sponge behavior 1 .
Sponges exposed to varying concentrations of ATP
Testing ADP and AMP metabolic products
Using PPADS to block P2X receptors
Examining ATP with glutamate interactions
| Chemical Applied | Sponge Response |
|---|---|
| ATP | Rapid, sustained expansion of excurrent canals |
| ADP | Complete contractions |
| AMP | No response |
| Glutamate | Complete contractions |
| Glutamate + PPADS | No contraction |
The most significant finding was that ATP works downstream of glutamate in a coordinated signaling pathway 1 . When researchers blocked the ATP receptors with PPADS, sponges no longer responded to glutamate by contracting.
While the ATP-glutamate signaling pathway explains part of the coordination mystery, it doesn't address how sponges detect changes in their environment in the first place. Recent research has uncovered a potential sensory organ: the osculum—the large opening through which water exits the sponge 9 .
The inner epithelium of the osculum is lined with non-motile cilia arranged in precise arrays perpendicular to the direction of water flow 9 . These cilia have the 9+0 axonemal structure characteristic of sensory cilia in other organisms, unlike the 9+2 structure of motile cilia.
When researchers exposed sponges to chemicals that block sensory function in these cilia (neomycin sulfate, FM1-43, and Gadolinium), the sponges' contraction responses were reduced or eliminated entirely 9 . Even more telling, removing the cilia with chloral hydrate or removing the entire osculum stopped contractions, with the effect being reversible in all cases.
| Reagent | Function |
|---|---|
| L-glutamate | Triggers contraction responses |
| ATP & ADP | Test purinergic signaling |
| PPADS | Blocks P2X-like receptors |
| Neomycin sulfate | Blocks cationic channels |
| FM 1-43 | Labels ciliary membranes |
| Gadolinium | Blocks mechanosensitive channels |
The presence of P2X receptor sequences in sponge genomes—one of which groups with vertebrate P2X receptors—suggests that the molecular building blocks of neural signaling existed long before true nerves 1 .
Rather than appearing out of nowhere, complex sensory organs may have evolved from simpler ciliary arrays that initially served basic monitoring functions. Arrays of primary cilia in sponge oscula could represent the first step in the evolution of sensory and coordination systems in metazoans 9 .
The humble sponge, long dismissed as a simple filter feeder, is proving to be far more sophisticated than previously imagined. Its ability to coordinate whole-body contractions using purinergic signaling by ATP working in concert with glutamate reveals an ancient chemical language that predates the evolution of nervous systems 1 .
These findings not only illuminate the evolutionary origins of animal coordination but also challenge our definition of what constitutes "simple" versus "complex" biology. The sponge's chemical communication system, with its graded responses and sensory cilia arrays, represents an alternative solution to the problem of biological coordination—one that has proven successful for hundreds of millions of years.
As research continues, sponges may yield further insights into how complex biological systems emerge from simpler components. Their enduring success reminds us that sometimes, the most profound mysteries in biology aren't hidden in the most complex creatures, but in the deceptively simple ones that have witnessed eons of evolutionary experimentation.