Annelida
Introduction:
The annelids includes marine worms, earthworms and leaches. They range in size from less than a millimetre up to 3 metres. Their bodies are segmented and they all have movable bristles (also known as setae), some posses some regenerative ability to heal segments removed from their bodies.
All annelids are coelomates - meaning they have a fluid filled body cavity in which their organs are suspended. This cavity supports their hydrostatic skeleton, the pressure of the fluid maintaining the body structure which the organism can manipulate to change shape or move.
Annelids are found worldwide in all type of habitat from oceanic waters and damp soils to more extreme environments such as hydrothermal vents in the deep sea.
In the museum the annelids can be found in outer cabinets 8 and 9
Adaptations:
Annelids are bilaterally symmetrical and posses a complete digestive system which runs through the body. They have a range of sensory receptors allowing them to detect light, vibrations and in some cases chemicals- which are processed by a simple brain.
They posses an internal hydrostatic skeleton- their body cavity is filled with water resulting in high pressure which acts as structural support to the body. Two different muscle types (longitudinal and circular) contract/relax moving the water into concentrated areas. Think of a water filled tube, if you squeeze one end the water moves to the other, and will return once the pressure relaxes. This keeps the worm's body rigid while supporting movement, allowing the worms to move around easily while swimming or burrowing as well as fit through oddly shaped passages or burrow into sediment to escape from predators.
Segmentation within the body provides opportunity for separate regions of the body to specialise into different tasks such as reproduction or feeding. In some cases segments can fuse together to form more complex and specialised structures.
Many annelids are exceptional burrowers owing to their hydrostatic skeleton and bristle-like structures called setae, which protrude from their body (except from leaches) which help sift through the sediment as they dig.
Classification
The annelids are classified into 3 groups based on the presence/absence of setea and their main habitat
Polychaeta
The marine worms.
These have lots of setae to aid in gaseous exchange and movement
Oligochaeta
The earthworms.
These have little to no setae and are found in soils
Hirudinea
The leeches.
They have no setae and posses a sucker to help with movement and feeding on blood
Futher explore the different groups of Annelids with OneZoom
Museum highlights:
Preserved twin heads and body of Lygdamis muratus also known as Devil Worm or honeycomb worm. This is a polychaete tube worm which stays burrowed in sea floor sediment, reaching out its heads with fan-like bristles to catch floating sediments for feeding. These worms build a protective tube from sand and shell fragments to defend against predators - which sometimes looks like a honeycomb.
Gossamer worm (Tomopteris sp) - known for their bioluminescent podia (leg-like outgrowths) which glow when the worm is disturbed
European medicinal leech - the largest of leeches to be found in the UK. These leeches feed off human blood, and have a history of use in the medical industry to remove toxins from blood, prevent clotting and in some cases of early medicine to 'bleed' patients as a form of blood letting to treat a variety of diseases.
Juvenile Megascolex earthworm around 45 cm in length. These worms are native to Madagascar, Australia, New Zealand, Southeast Asia, and North America and can gorw up to 2 meters in length. They form an essential part of the ecosystem, helping to maintain soil structure and distribute nutrients.
Parchment worm Chaetopterus variopedatus and protective tube made up off sediment and small shell fragments. The tube covers the worm as it nests in a burrow, hiding from predators. Both ends of the worm stick out from the burrow when feeding, where the worm draws in water through the anterior end and out the posterior and traps food particles within its body using mucus and tentecle like structures
