FIGURE 90.15 Marine invertebrate causing human sting Class Hydrozoa Feathered hydroid (Pennaria tiarella ) is found from Maine to Florida and along the Texas coast just below the low-tide line They attach to solid objects, including pilings and floats They cause a mild sting that may be treated with local care Portuguese man-of-war (Physalia physalis ) is a hydrozoan colony, although it is commonly erroneously considered a jellyfish The float can be up to 30 cm in length, with tentacles hanging from the float that may reach more than 75 ft in length and contain about 750,000 nematocysts each This open-sea animal is often driven ashore by storms along the Atlantic coast Tentacles on the skin should be fairly easy to recognize as the cause of symptoms Releasing one of the most powerful marine toxins, the nematocysts of