Ice Worms
Exploring the Ocean Bottom

In July of 1997 Fisher and McDonald used the submersible Johnson Sealink II to get to the sea floor of the Gulf of Mexico. At about 240 kilometers off the east coast of Texas and over 550 meters deep near the bottom muds, they expected to examine mounds of an icy substance known as methane hydrate. This "ice" forms when methane gas seeps up through underwater fissures and combines with water at low temperatures and high pressure. Methane freezes at higher temperatures than water, around 6 degrees centigrade. When combined with the seawater, large mounds of this unique ice build up. Because it is less dense than the surrounding water, it builds up into large mounds very easily.

Check out this deep-sea submersible used for seafloor exploration!
http://www.bio.psu.edu/People/Faculty/Fisher/cold_seeps/