I think that perhaps because of the North American Echinoderm Conference in full swing that the news is chock full o' echinoderm news this week!
Sea Urchins are apparently 'cacophonous' eaters!!
with the scientific citation here.
Craig Radford & associates at the Leigh Marine Lab in Auckland, New Zealand have found that the New Zealand sea urchin Evechinus chloroticus apparently creates LOUD FEEDING NOISES in the 800-2800 Hz range.
Timing of this increase in noisiness coincides with feeding habits of the sea urchin.
Apparently the test acts as a Helmholtz Resonator which, according to Wikipedia is described thusly:
When air is forced into a cavity, the pressure inside increases. Once the external force that forces the air into the cavity disappears, the higher-pressure air inside will flow out. However, this surge of air flowing out will tend to over-compensate, due to the inertia of the air in the neck, and the cavity will be left at a pressure slightly lower than the outside, causing air to be drawn back in. This process repeats with the magnitude of the pressure changes decreasing each time.which amplifies the ambient sound intensity in coastal waters by as much as TWO TO THREE ORDERS OF MAGNITUDE.
Honestly. I never get tired of writing about echinoderms.