In some plants of angiosperms, the pollen grains are long and ribbon like and covered by a mucilaginous covering. Such plants show pollination by the agency of 

Long ribbon like pollen grains are seen in hypohydrophilous plants like Zostera. Pollen grains of such plants are covered by mucilaginous covering to prevent the pollen grains from wetting. Water is involved in pollination of such plants.