What is "hydra," (the animal/plant in salt water)?

Question

I was recently diving in Cozumel, MX and our divemsater said not to touch something called "hydra" I got stuck in a cave hole and struggeled and touched some hydra, it has been about a week scince the first touch, when will the rash/bumps go away, or is there something that I can use to get rid of it?

Answer 1

Hydra is a genus of simple, fresh-water animals possessing radial symmetry. Hydras are predatory animals belonging to the phylum Cnidaria and the class Hydrozoa. They can be found in most unpolluted freshwater ponds, lakes and streams in the temperate and tropical regions by gently sweeping a collecting net through weedy areas. They are usually a few millimeters long and are best studied with a microscope. Biologists are especially interested in hydras due to their regenerative ability. Hydras appear to be unique among animals in that they do not undergo senescence (aging).

Hydra is a small animal with a body length ranging from 1 mm to 20 mm when fully extended. It has a tubular body secured by a simple adhesive foot called the basal disc. Gland cells in the basal disc secrete a sticky fluid that allows for its adhesive properties. At the free end of the body is a mouth opening surrounded by one to twelve thin, mobile tentacles. Each tentacle, or cnida (plural: cnidae), is clothed with highly specialised stinging cells called cnidocytes. Cnidocytes contain specialized structures called nematocysts which look like miniature light bulbs with a coiled thread inside. At the narrow outer edge of the cnidocyte is a short trigger hair. Upon contact with prey, the contents of the nematocyst are explosively discharged, firing a dart-like thread containing neurotoxins into whatever triggered the release. To humans, this poses a nuisance at worst; however, to some prey, this strike can be paralyzing.

Hydras mainly feed on small aquatic invertebrates such as Daphnia and Cyclops. All species of Hydra exist in a mutual relationship with various types of unicellular algae. The Hydra affords the algae protection from predators and in return, photosynthetic products from the algae are beneficial as a food source to the Hydra .

Hope that helped

To summarize, you weren't allowed to touch it because it's a predatory animal. Its nematocyst are explosively discharged, firing a dart-like thread containing neurotoxins into whatever triggered the release. The friend of yours who touched the hydra poses a nuisance....but it may lead to paralysis.

Answer 2

a hydra is among the first evolutionary/ life cycle stages of a jellyfish. when you touched the hydra, it released some nematocysts, kinda like little poison torpedos into your skin. Treat it like you would a normal jellyfish bite. some vinegar, or maybe, just throwing it out there. you should see a doctor. Its more if it lasts 2-3 weeks, then I would get seriously worried though