Hydroids

 

PZNOW

Shorelife

Coelentrates

Sea Anemones

True Jellyfish

Hydroids

Hydroids are colonies of polyps. Each polyp is similar to a small sea anemone i.e. has its own jelly like body and a mouth surrounded by tentacles. The difference is that individuals are organised to benefit the whole colony. They do this, by being interconnected via a common tube the stolon. The stolon which can be tough and horny, allows the transfer of food between the polyps.

Hydroids have interesting life cycles, which vary depending on the species, but generally they go through three stages.

1.      Free swimming planktonic larvae that settles and forms sessile polyps.

2.      The polyps produce free swimming medusa (small jellyfish like stage).

3.      The medusa in turn produce planktonic larva.

To find hydroids one has to look on the lower shore particularly during spring tides when the kelp is exposed. They will be found attached to seaweeds and rocks. They are not always easy to find as many are small or form seaweed like colonies. Many species do not possess a non scientific name The species found in Cornwall include the Sea Fir Obelia geniculata, Sea Oak Dynameita pionila, and Clava multicornis.

 

 

 

The hydroid pictured here was found on a floating plastic crate.

The crate had been at sea for some time, as there were many mature goose barnacles attached to it.

The crate was covered by hundreds of 'fine hairs'. This is a magnified image of two of the 'hairs'.

 

Magnified image of a hydroid..

 

Included within the hydroids are jellyfish like creatures that are easily confused with true jellyfish. Two species commonly confused are the Portuguese Man of War, Physalia physalis and the By-the-wind sailor Velella velella. Both species are not true jellyfish but free floating hydroids. Both are regularly stranded on Cornish shores, particularly the By-the-wind sailor which can be stranded in the thousands.

 

Species of Hydroids Found In Cornwall

 

     By-the-wind-sailor Velella velella

  Portuguese Man of War Physalis physalis

 

By-the-wind-sailor Velella velella

They are under four inches long and are a distinctive deep blue. They possess a float with small blue tentacles on the underside, used to catch their prey.

To aid transportation they have a transparent sail, which can be either left or right handed. Winds tend to distribute them into groups comprised of the same handedness, so strandings tend to be made up of one group.

 

 

 

By The Wind Sailor

 

By The Wind Sailor

 

 

 

Portuguese Man of War Physalis physalis

This is the most well known (infamous) hydroid. It has a float which is up to a foot across. On its top is a sail which stands high out of the water, catching the wind so enabling transportation.

This jellyfish should not be touched as its sting can be fatal, or approached, as its stinging tentacles can exceed 60 feet.

The diagram shown here is only a rough diagram, but is included as this is an animal of which one must stay clear .

 

Portugese Man Of War

 

 

FREE ADVERTISING
Free advertising
available on this web site.

SEND US YOUR PHOTO OR INFORMATION
Of shorelife in Cornwall and the UK. All are credited.

WANTED UK SHORELIFE SITES TO LINK TO 
A reciprocal link required.

 

PZNOW   Penzance   Accommodation   Local Attractions   Elsewhere in Penwith   Historic Past   Weather   Geology   Local Art
  
Shore Life   
Wildlife   Web Design   Local Music   Activities   Site Map   Disclaimer   Contributions  

 

 

 

  email: pznow@btopenworld.com