Sunday, 14 December 2014

Creature 75: Hydra

This animal is immortal

Today I am looking at a genus called Hydra, which may sound like a mythical creature, particularly when we start throwing words like immortal around, but I assure you they are 100% real.

Hydra are in the jellyfish group Cnidaria and like other members of the group they sting with cells called Cnidocytes.  They can usually expand in size to about 1 cm long. They have a tubular body small tentacles at one end and an adhesive foot at the other. They use their foot to attach themselves to substrates on which they remain sessile most of the time. They detach themselves and swim around when hunting. Their tentacles are densely covered in neurotoxin loaded cnidocytes. When hunting they grab their prey with their tentacles and deliver the neurotoxin which usually kills their prey quite quickly. While the neurotoxins are fairly potent they do not deliver enough to have an effect on humans. These are used to deadly effect when When conditions are good Hydra reproduce asexually by budding clones off their body. When conditions are unfavorable they grow gonads and begin reproducing sexually.

Like the Hydra of Greek mythology from which its name derives, the Hydra can regrow damaged body parts. They never age and their stem cells can go on renewing themselves indefinitely. These characteristics make the Hydra theoretically immortal. They can still be killed by damage like an elf in the Lord of the Rings, and they can be killed by disease or starvation but assuming favorable conditions a Hydra will go on living forever.

Hydra are one of the few freshwater Cnidarian groups. They live in freshwater ecosystems all over the world.

Kingdom: Animalia
Phylum: Cnidaria
Class: Hydrozoa
Order: Anthomedusa
Family: Hydridae
Genus: Hydra

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