Cnidaria
Introduction:
Cnidaria includes jellyfish, hydroids, sea anemones, corals and even some lesser known marine parasites. They are aquatic animals found in both freshwater and marine environments. Their name translates from the Latin word cnidos meaning 'stinging nettle' relating to their specialist nematocysts which eject barbed threads tipped with poison - causing a nasty, even fatal sting. They are radially symmetrical
Another recognisable key feature of this group is the two forms in which they exist:
The polyp form - sessile and unable to independently move. Faces up similar to a tree.
The medusa form - active and free swimming. Face down in an umbrella-like structure
In the museum cnidaria can be found in the outer cabinets 2 and 3
Adaptations:
Developing from the simple design of the sponges, cnidaria have developed in complexity with specialised cells organised into 2 tissue layers the outer epidermis and the inner gastrodermis. This is different from 'higher animals' (everything that isnt within porifera or cnidaria) which has 3 layers.
Within the epidermis cells for movement and structure support the shape of the cnidaria. In addition it contains receptor cells for navigating its environment, intestinal cells which can transform into other specialist cells to fix damage and support growth, and the cindocyte cells which contain the specialist nematocyst stinging apparatus.
Within the gastrodermis cells aid digestion via releasing enzymes and controlling the uptake and movement of food, alongside removing waste.
Many cnidarias are equipped with tentacles which the use to aid swimming, feeding and hunting- a dangerous combination when combined with their potent poison stings. Useful as most cnidarians are carnivores.
Classifications:
Cnidaria are classified based off their life-cycles, body form (medusa vs polyp)
Hydrozoa
Hydra and siphonophores
Scyphozoa
True jellyfish
Cubozoa
Box jellies
Anthozoa
Sea anemones, corals and sea pens
Explore the different cnidaria groups with this interactive phylogeny tree from OneZoom
Museum Highlights:
By-the-wind-sailor: a marine hydrozoan found in in warm and temperate waters in all the world's oceans. Similar to the Portuguese Man O'War, this organism is part of the siphonophore group, in which all organisms are formed of colonies of zooids - genetically identical clones which all have various forms and functions that contribute to the animal as a system. These cnidaria are known for their recognisable 'sail' - a balloon like float which is visible above the water, unlike the long strands of tentacles and polyps which extend below the water
Chiropsalmusbox Box Jelly- a voracious predator that hunts fish, worms and crustaceans, taking on prey almost double it's size using it's extensive long tentacles and immobilizing venom.
Assortment of both stony and soft corals including the Gorgon Coral Muricea chamaeleon - known for their large branching structures (up to 3 feet in height and width) and bright colours.
The familiar moon jellyfish Aurelia aurita, a common UK species that often wash up on beaches.
Mauve Stinger jellyfish - a bluey-purple jellyfish with tentacles up to 3m long found offshore of the UK and in warmer European waters. These are known for their painful stings and their bioluminescent glow when hunting at night.
