Snails can have a long life. The life span for snails depends on their habitat and the species. Some of them only live for about 5 years. However, others in the wild are believed to be up to 25 years old in unusual occasions. 3.
Facultative means optional or discretionary (antonym obligate), used mainly in biology in phrases such as: 1  Facultative anaerobe, an organism that can use oxygen but also has anaerobic methods of energy production. It can survive in either environment. Facultative biped, an animal that is capable of walking or running on two legs as well as walking or running on four limbs or more, as appropriate.
Some symbiotic relationships are obligate, meaning that both symbionts entirely depend on each other for survival. For example, many lichens consist of fungal and photosynthetic symbionts that cannot live on their own. Others are facultative, meaning that they can, but do not have to live with the other organism.