Leeches, Worms, & Planaria
Worms are actually many different animals from several major unrelated invertebrates that share a similar body shape. Worms generally have long thin and soft bodies.
Leeches, tubifex and earth worms are all in the same phylum, Annelida, meaning segmented worm. Annelids have bodies made of a series of segments.
Planaria, which are commonly found in the aquarium are from the phylum Platyheminthes. Planaria are a type of flatworm. They are mostly scavengers whose bodies are not in segments.
Leeches (often misspelled leach or leaches) are flattened segmented worms with a sucker on both tail and mouth. They move by attaching the mouth sucker, then tail sucker, then mouth sucker, and so on, flipping along the surface similar to an inchworm.
Drawing of medical leeches from, "Freshwater Aquaria" by Rev. Gregory C. Bateman, 1890.
Most leeches live in the water, though some can survive dry periods water by burrowing in the mud. Some leeches even live in moist environments on the land. Most leeches avoid light.
Unlike some worms leeches always reproduce sexually, even though they are hermaphroditic. Care of the young varies. Some leeches leave cacoons of eggs to care for themselves while others remain attached to the parent.
Leeches are most commonly known for attaching on to humans and other animals, and sucking their blood. Blood sucking leeches have well developed jaws. Different types of leeches feed on different animals, though there are also some that eat plants, and some that feed on carrion. Leeches are not often found in the aquarium. Some of the leeches that feed on humans secrete a substance that has been found to be an anticoagulant.
Tubifex are true worms, related to the earthworm. They are up to about 1 inch long, red in color and get the color from blood showing through their body. Tubifex worms are bottom dwelling and live in tubes. They live head down with their tails waving out of the top of the tubes. They sift through the mud looking for food. Tubifex worms are often found in dirty water. They are also a very popular fish food.
Planaria are a type of flatworm. Flatworms are related to flukes, tapeworms, and other parasitic worms. Planaria are a larger flatworm from the suborder triclads.
Planaria can reproduce both sexually and asexually, though they can't fertilize their own eggs. They can reproduce asexually by splitting in the middle to form clones of themselves. In fact if cut in to several pieces most will grow into a new planaria. The different methods planaria use to reproduce may depend on the conditions of the animal's current environment.
Planaria are often confused with leeches, though they can be told apart easily be visual observation. Planaria have horn like protrusions from the sides of their head and eye spots. The mouth of the planaria is the only opening to its digestive system and is located under the middle of its body.
Planaria can be a problem in the aquarium in tanks with egg laying fish that don't protect their eggs. The planaria can eat the fish eggs. Most planaria are scavengers of some sort but they are also often very opportunistic and will eat anything they can and this may include fish eggs. Planaria are also very hard to remove from the aquarium once established, they will also easily transfer to other aquariums on plants.
| Moss Animals
| Leeches, Worms, and Planaria
| Small Crustaceans
| True Bugs
| Ramshorn Snails
| Pond Snails
| Malayan Livebearing Snails