High numbers of a species of jellyfish that can grow to huge sizes have been sighted in recent months in the Gulf of Maine and some of its beaches. The lion’s mane jellyfish, believed to be the world’s largest, can grow to five or more feet across, with tentacles more than 100 feet long. Such huge jelliyfish are uncommon, but larger-than-average ones have been more common this year, according to beachgoers. Nick Record, a senior research scientist at Bigelow Laboratory for Ocean Sciences, says he typically gets 300 to 700 reports of jellyfish per summer. This year’s total number of jellyfish is likely to be about average.