Not so simple as you might think

Oren Pazgal


Vu-PAP Bio-1


  • Students will be learning about the external and internal anatomy of an earthworm.
  • Students will focus on the organs, structures, and functions of the digestive system.
  • Students will also understand the ecological role of the earthworm.

Lumbricus terrestris

Earthworms are classified under Phylum Annelida, which means that they are invertebrates, segmented, and soft-bodied. Earthworms are also some of the simplest coelomates, meaning they have a body cavity. The worm is essentially a "tube within a tube." As simple as they might seem, you might not expect earthworms to live for a full six and a half years. They reach sexual maturity at about a year of age, at which point a clitellum develops. Worms are hermaphrodites, so when it comes time to mate two worms line up their male gonads (testes) with the other's female gonads (ovaries) and release their sperm and eggs into the other worm through a mucus sheath created by the clitellum. During fertilization, the eggs and sperm will be encased in a cocoon where fertilization will occur. A young worm will break free of this cocoon after several weeks. Then it will grow, reach sexual maturity, and continue the cycle

Earthworm Evolution (Eartholution?)

One of the most important adaptations that the earthworm has evolved is the ability to respire through its skin, which allows it to comfortably live underground, which it would be unable to do if it had lungs. As an annelid, it possesses a segmented body and streamlined shape, which are both very conducive to burrowing through soil, and have also been naturally selected for their habitat. In fact, earthworms are very well adapted to underground life in all respects. Instead of eyes, ears, a nose, or ears, Lumbricus terrestris has evolved specialized sensory organs that perform the same functions without hindering its ability to function in such a confined space. Another important evolutionary milestone that the earthworm has is a coelom, or body cavity- a characteristic that places the earthworm far above its predecessors.

Ecological niche

Earthworms are detritivores, but they also function as decomposers for their ecosystems. In some cases, they serve as primary consumers as well. More importantly though, earthworms enrich and oxygenate the soil around them, which helps plant life flourish and the ecosystem to thrive.


Highlight: The digestive system

The earthworm consumes soil through its mouth on the anterior end of its body. The soil moves into pharynx which is the equivalent of the worm's throat. From there the soil passes through the esophagus and into the crop, where it is stored. After that, the digested soil enters the gizzard, where rocks that the worm has swallowed grind up the soil completely. The gizzard leads to the intestine, where glands release fluids that aid in digestion, until eventually the waste that had no use for the body in terms of nutrients is expelled through the anus, all the way at the posterior end of the worm.

Works Cited