Armor and Marine Corps Historians step up...I need your help.

Photo caption: "Iwo Jima, February 21, 1945. Burrowed in the Sand: A Marine medium tank that couldn't navigate the soft volcanic sand on Iwo, is track deep in a pit off the beach. This loose sand of the island proved an asset to the Japanese defenders."
From the Photograph Collection at the Marine Corps Archives and Special Collections
OFFICIAL USMC PHOTOGRAPH
Notice the barbs around the crew hatches?  I haven't seen it on another vehicle and there is no indication of why (I assume they're anti-personnel in nature) this particular crew applied them.  Also missing is whether or not this was a platoon level modification or higher.  Any info would be appreciated.