Long Island Sound's Jellyfish
Lion's Mane: Cyanea capillata
"The world's largest jellyfish. Typically to 12 in. ... but can reach 8 ft. ... Most specimens south of Cape Hatteras are small (5 in. ...), but individuals increase in size in North Atlantic. A classic jellyfish, ranging in color from brownish to pink. Extremely long tentacles and massive cascading group of mouth lobes. Range: North Atlantic to Carolinas."
Moon jelly: Aurelia aurita
"Familiar jellyfish of bays, sounds and inland waters. Bell edge rimmed by short fringe of tentacles. Prey captured in mucilaginous cap and 'cleared off' for ingestion by elongate mouth arms that drape below. Easily identified by distinct shamrock appearance of gonads seen through transprent cap. Range: Extreme northern Greenland to Caribbean. Size: To 10 in..."
Ctenophores, or Comb Jellies:
"Often mistaken for jellyfish. However, comb jellies do not sting, have two tentacles or lobes below their sac-like body, and have up to eight comb-like ciliary plates. Gelatinous and fragile, they turn into nondescript blobs out of water. All are plankters (drifters with little self-locomotion) and can amass in large swarms. They are predators of small fish and fish eggs. Note: when viewing comb jellies, look for pinkish worm-like forms in the gut region. These are the parastic young of the Burrowing Anemone..." (I'll be sure to do that, as soon as I finish looking at the moon jelly's gonads.)
I think the Lion's Mane is the only one that stings and although it can grow to eight feet in size, it doesn't come close to that in our area. Jellyfish (as opposed to comb jellies) can swim, so technically they're not zooplankton, which drift with the currents and tides.
The photos are from here and here, on Flickr.