Is the relationship between Riftia pachyptila and the chemosynthetic bacteria an example of symbiosis?

YES. The relationship between Riftia pachyptila and the chemosynthetic bacteria is an example of SYMBIOSIS.

Explanation:

Nutrition is the series of process by which living organisms obtain food substances and use them to provide energy and materials for their growth and maintenance. There are 2 major modes of nutrition which includes:

--> Heterotrophic nutrition: this is the type of nutrition in which the organism depends on manufactured food for survival. Heterotrophic organisms may be SYMBIOTIC which means that it can live together with another organism as they both benefit from each other.

--> Autotrophic nutrition is the type of nutrition in which an organism has the ability to manufacture its own food. This can be achieved through the process of CHEMOSYNTHESIS. In this process, they synthesis organic compounds with the use of energy from inorganic compounds such as carbondioxide. An example is the chemosynthetic bacteria found in the gut of Riftia pachyptila.

Riftia pachyptila is an aquatic invertebrate that is seen at the seafloor near hydrothermal vents ( high temperature area). They do not have digestive system that will enable them make use of the inorganic materials (carbondioxide, sulphide) found in their environment. But within their paired coelomic cavities are chemosynthetic bacteria.

The relationship between Riftia pachyptila and the chemosynthetic bacteria is an example of SYMBIOSIS because the chemosynthetic bacteria depends of the Riftia pachyptila for the necessary inorganic compounds for its own metabolic reactions and excretion of by products while Riftia pachyptila depend on the bacteria for byproducts from its metabolic reaction which is needed for its growth.

explanation:

the fossil record extends back to a dog-like ancestor some 55 million years ago, which gave rise to the first horse-like species 55 to 42 million years ago in the genus eohippus.