Methane seep ecosystems are based on methane hydrate, a crystallized form of methane. Although it looks remarkably similar to ice, if you hold a match to methane hydrate, it will burn—thus its nickname "fire ice". It has a much higher melting point than water and it is a poor conductor of heat. Even though it is frozen, it doesn’t feel cold when you touch it.
In 1997, ice worms (pictured - top) were discovered living on the surface of methane hydrate, their principle source of food being methane eating bacteria. Other organisms have also been found subsisting on the methane including mussels, clams and 100 year old tubeworms. The mussels and clams have developed a symbiotic relationship with methane eating bacteria. Without these bacteria to metabolize energy for them, the mussels and clams would not survive.