Subterranean means under the surface of the earth, or underground. There is a whole world living beneath your feet, whether it is in the soil or in caves.
Life in the Soil
You might think of it as just dirt, but there is an entire ecosystem living under your feet, and the rest of life on Earth depends on that ecosystem. Soil organisms are responsible for the majority of decomposition of animal waste products and dead plants and animals. Without these decomposers, the waste and remains of plants and animals would just pile up and the plants would have no nutrients to help produce energy for the terrestrial ecosystems.
Explore the image below to see a small sample of what lives in the soil.
(Hover to identify or click to enlarge)
Image provided by Dr. James Nardi, from his book The World Beneath Our Feet: A Guide to Life in the Soil; coloring poster available here
The most numerous groups in order of abundance are bacteria, actinomycetes, fungi, cyanobacteria (also known as blue green algae), protozoans, and invertebrates. The most numerous invertebrates are nematodes, mites, springtails, potworms, snails and slugs, earthworms, and centipedes and millipedes.
Cool fact: Some antibiotics used by humans, are produced by soil organisms. Penicillin is produced by some soil fungi and Streptomycin, Neomycin and Tetracyclines are produced by some actinomycetes.
Life in Caves
A cave is a natural underground opening or cavity in rock, typically defined as large enough for a human to enter, but for our purposes includes passages too small for humans.
Within caves, there can be a variety of habitats. Some terrestrial cave habitats include flood debris, animal feces, clay floors, rock floors, and bedrock walls and ceilings. Cave streams and drip pools provide aquatic habitats.
Terms for cave organisms:
Troglobite – must live in a cave
Troglophile – lives in a cave but can live above ground
Trogloxene – uses caves for shelter but does not need to live there
Edaphobite - must live in the soil
Animals living in caves are adapted to life in the dark. Adaptations may include reduced coloration, reduced vision, smaller size, and an increase in antennae or sensory hairs.
Speleothems – Cave deposits formed usually of calcite
Stalactite – speleothem hanging from roof, formed by dripping water
Stalagmite – speleothem growing upwards from cave floor, formed by precipitation of drips, often under a stalactite.