Resembling a cross between an octopus and a sea anemone, tiny hydra lives in fresh water. It would make an excellent subject for a Japanese sci-fi movie. H. oligactis, seen at left, has a central stalk from which a number of tentacles radiate.
The Real Deal
Waving its tentacles in search of prey, the tiny creature thrives in among loose weeds. The creatures are carnivores. Scientists find them of special interest because of their great ability to regenerate.
They are capable of living a long time. The base of the stalk secretes an adhesive that enables the miniature “octopus” to stick to surfaces. The tentacles contain nematocysts or stinging cells with neurotoxins that paralyze a victim.
In addition to its regenerative ability, the animal produces its own bactericide, the anti-microbial protein hydramacin-1. Although this aquatic animal possesses exotic features, it does not possess an organelle comparable to a brain. Neither does it possess one or more eyes, or true muscles.
Where in the Food Chain?
The hydra feeds primarily on daphnia and cyclops. Its greatly extensible tentacles wrap around the prey, paralyzing it. Then they pull the prey to its opened mouth. After a couple or a few days, hydra regurgitates the remains. Here is a 21-second video of one catching a daphnia.
What feeds on the the tentacled creature? What indeed! Although hydras, themselves, can eat very tiny fish fry, there are fish that, in turn, consume them. One variety familiar to tropical fish aquarists is the three-spotted gourami. There are some others, including the paradise fish. In addition, snails will consume hydras.
Interestingly, the genome for our tiny friend has been sequenced. It is of keen interest to researchers of Huntingtons and Alzheimers diseases. In fact, it is hoped its biology will shed light on “birth defects, cancers, and other developmental diseases.”
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- Developmental Biology Interactive: Hydra
- Fairfax County Public Schools: Green Hydra
- University of Wisconsin, La Crosse: Zoo Lab: Hydra c.s. (Class Hydrozoa)