The Hydra Lab
Not the one
from
Hercules!!
Cnidarians (formerly coelenterates) have two cell layers, tentacles
armed with stinging cells, a single-ended digestive cavity, and a
nerve net that allows some general responses to environmental
stimuli. In 1997, scientists succeeded in cloning a mammal, but
cnidarians have been in the cloning business for close to 600 million
years. One of the best examples is seen in the common fresh-water
Hydra, a cnidarian that reproduces by "budding."
Class Hydrozoa
Hydra captures microcrustaceans, swallowing and digesting them in
its gut. It uses two methods of digestion. One is primitive —
engulfment of small food particles that then are digested in vacuoles
located in the phagocytic cells lining the gut (the same methods used
by amoebas and other phagocytic protists). Extracellular digestion
also occurs. This process is initiated by hyfrolytic enzymes produced
by gland cells in the gut lining. The absorbed nutrients diffuse to the
outer layer of cells without the requirement of a circulatory system.
Undigested material is regurgitated through the mouth, one
shortcoming of a single-ended gut. With minor variations, this is the
Stinging cells inject paralyzing poisons and enzymes that begin the
process of digestion even before the prey is swallowed. Trigger hairs,
brushed by a daphnia's antennae, fire out their darts and lashes.
Note the violent response to contact shown by Daphnia and the red
copepods used in feeding trials. As the poisons take effect, the prey
rapidly looses its ability to resist.
Hydras move by looping, basically somersaulting to a new location.
The green hydra harbors symbiotic algae in its tissues. Although it
receives some nutrients from its photosynthetic guests, Chlorohydra
eats a balanced diet, gorging on microcrustaceans when available.
Budding new individuals from a few cells located on Hydra's lower
body is a natural form of cloning. The individuals produced are
identical genetically to their mother or father. Sexual exchanges
shuffle the genetic deck, usually just before winter sets in. Fertilized
eggs withstand freezing, producing a new hydra in the spring.
Longitudinal Section
Cross Section
Here we see a cross section through
the body of a Hydra sp. Note that
the body wall is only made of two
layers, the outer epidermis, and the
inner endodermis.
Ingesting a Daphnia
Do they ever stop eating?
The Hydra Budding
Here you can see a photo of a
Hydra sp. with two asexual
buds.
Chlorohydra viridissima
Here you can see
an image of a
Hydra sp. with Sexual Organs
ovaries growing
in the body wall.
In this image
you can see the
testes growing
in the body
wall.