Pond Life: Hydra

Freshwater Coelenterates

Hydra reproduce both by budding and sexually. They can move slowly by turning somersaults and can conract into a gel-like ball or extend to many times their contracted size.

Brown Hydra

Hydra vulgaris


Projectina Microscope
Objective: Projectina x10 macro (long wd)
Ocular: Watson x8 Compensating
Substage condenser with top lens removed
Substage wheelstop
Sample from Warnham Pond and stored for a few weeks

Camera: Canon Powershot S50
ISO 100, F4.9, 1/1000sec


Showing ingested Daphnia

The "knobbly bits" on the tentacles are stinging cells or cnidoblasts

Zeiss GFL Microscope
Objective: Plan 0.03 - 5.0 variable
Ocular: Watson x8 Compensating
Surface illumination

Camera: Canon Powershot S50
ISO 50, F4.9, 1/40sec

January 2005

Green Hydra

Hydra viridissima

Semi-contracted green hydra
The green colour is due to symbiotic algae (zoochlorella). These are not present in the outer layer of cells. This can be seen more clearly in the image below.

Microscope: Zeiss Standard GFL
Objective: Zeiss 10/0.22 plan achro
Ocular: Olympus P15
Brightfield/blue filter
Camera: Canon Powershot S50
Sample from Warnham Millpond 08-Oct-2006


Tentacle tip
The green zoochlorella can be clearly seen as can the cnidoblasts, some of which have discharged their nematocysts. The cnidoblasts are the rounded cells with a keyhole like central feature. The faint lines perpendicular to the tentacle surface are where the nematocysts have discharged releasing harpoon like barbs used for paralysing prey.


Microscope: Zeiss Standard GFL
Objective: Leitz 40/0.7 NPL Fluotar ICT
Ocular: Olympus P15
Substage: Leitz ICT
Differential Interference Contrast
Camera: Canon Powershot S50
ISO200, F4.9, 1/8 sec
Sample from Warnham Millpond 08-Oct-2006