Jellyfish - hydroid forms

Code IB010000

Solitary hydrids (genus Hydra ) of ponds and streams, often found on twigs or vegetation. The body is a simple tube-shape with tentacles around the mouth. Size is variable, up to about 3mm when extended, but all species are highly contractile. Colours vary from whitish to green.

Hydrids are slow-moving, and creep on the ab-oral "foot" or progress by a "cartwheel" or somersault motion. Reproduction is mostly by budding, but egg and sperm cells are produced seasonally or in response to environmental triggers. Fertilised eggs hatch directly into small hydra without going through a medusoid (jellyfish) stage. Small flatworms of family Temnocephalide, commensal on Crustacea and sometimes on other animals, may sometimes be mistaken for Hydra .