By Antonio Bronic PULA, Croatia (Reuters) – A huge clam that was on the verge of extinction has made a comeback, with a surge in numbers in waters off Croatia, marine biologists say. The clam, known as the noble pen shell or pinna nobilis, started dying out as a deadly pathogen spread in parts of the Mediterranean around 2016. Numbers plummeted across the region and, until recently, scientists in Croatia only knew of around 10 surviving in their corner of the Adriatic. Then last year a diver spotted a group of 20 near the shore in the north of the Istria peninsula. “The news sounded incredible…