HYDRAS AND JELLYFISH  - LAKE ERIE - CENTRAL BASIN - AVON POINT

The two animals below are members of the Phylum Cnidarians. They are freshwater hydras. These predators live on the underside of the rocks throughout the reef area of Avon Point. They are between 2 and 5mm. long and during the months from late May to July they are found on the reef by the thousands. Members of the phylum Cnidaria have one organ unique to the phylum and that is the nematocysts. 

. If you look closely at the tentacles seen below you can see numerous small dots or bumps running along the arms, these bumps are the nematocysts. The nematocysts are small barbs attached to a strand that is shot out of the tentacle when prey gets near any of the tentacles. The barb has a type of poison that immobilizes the prey. Paralyzed, the prey is pushed towards the mouth by the tentacle. The mouth is the bubble like structure at the center of the tentacles ring. I have seen animals half the size of the hydra itself ingested. 

Hydras reproduce by budding. Below, young hydra attached to the parent's stalk. When the new hydra achieves a certain size it will break away and live independently.

The picture below is of the hydranth of another type of hydra that lives on the reef, the colonial hydra, Cordylophora lacrustris.The tentacles of these animals are not as long as those of the hydra and all of the hydranths are joined together at their base by a tube known as the hydrorhiza. A colony on the reef may have as many as 30 to 40 hydranths and cover an area of 3 to 4 sq. cm. These colonies live on the underside of rocks.

Lake Erie is one of the few freshwater bodies in the world that these animals have been found living in as they are marine (salt water) creatures.

Up until this year (2000) the colonies were normally not found until early fall but for some unknown reason they are being found in early June. 

The picture below is of an unknown species of hydra (unknown to me). It is a solitary hydra, the hydranth is about 1 mm. long, the whole animal is about two mm. long. It was not found living on the rocks surface but rather it had attached itself to some organic matter living on the underside of a rock.

The photo is a view of the hydra seen at 200X 

Below is a picture of a jellyfish. Since I became familiar with the animals of the Phylum Cnidaria I strongly hoped that I would one day get to see one in the Lake's water. After about twelve years of looking I have finally found one. The one below is I think of the genus Craspedacusta (though I could easily be wrong on this). It is about 2 mm. in diameter. The jellyfish was found at Avon Point on May 28, 2000.