Freelance photographer Mike Newman said he spotted "great numbers" of the pods when he was surfing on Long Rock beach in Cornwall.
The objects have reportedly baffled holidaymakers who were concerned they were poisonous.
But marine expert Prof Martin Attrill said they were harmless "sea potatoes".
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More formally known as burrowing sea urchins, Prof Attrill said they were about the size of a tennis ball and were usually covered with little spines.
Prof Attrill, from Plymouth University, said mass strandings of sea potatoes were "not unusual", particularly because they aggregated for breeding, meaning many could wash up together when caught out by a storm.
"There does seem to be a lot of them at the moment, but we have had a couple of pretty strong storms over the last week or two," he said.
Mr Newman said his children thought they were "fun to play with", and he had no concerns that they were poisonous.
"They are quite cute," Prof Attrill added.
"Thousands" of "funny" baseball-like sea objects strewn across beaches in the South West have been identified as a common type of sea urchin.