Segmented Worms Flashcards
What are segmented worms ?
-Include earthworms,bristle worms and leeches.
-most segmented worms live on or within the bottom substrate, with few being planktonic in marine environment
What are earthworms
-Terrestrial invertebrates beloning to the order Opisthapora and phylum Annelida
- they are cylindrical segmented worms as they look like many little rings joined or fused together.
- usually have about 100-150 segments and depending on the species
- a mature earthworms size can vary from 10mm up to 3m
What are the 3 groups or ecotypes earthworms can be divided into based on their feeding and burrowing behaviour ?
Epigeic - live on soil surface feed on rotting plant and animal material
Endogeic - live within top 30cm of soil form horizontal tunnels and ingest soil in order to absorb nutrients from degraded organic material
Anecic - dig deep down within the soil during the day and come onto the surface during the night to feed and deposit their casts, form deep, permanent vertical tunnels in which they move to the surface to feed
Explain the anatomy and senses of an earthworm
-Do not have lungs or a nose
- breath through their skin via air dissolving on the mucus of their skin so their skin needs to stay moist( need to stay moist to allow for passage of dissolved oxygen into their blood stream)
- as fresh air is taken in through the skin, oxygen is drawn into the warm circulatory system, the worms heart pump the oxygenated blood to the head area. And as the worm moves blood is pumped to the back of the body and hearts pump blood forward again
- carbon dioxide dissolves out of the blood back to the skin
-Earthworms don’t have eyes but have receptor cells in their skin sensitive to light and touch(move away from light)
- simple brain that provides specialisation to direct its body movement in response to light
-no ears however can sense vibrations of animals moving nearby
-have five hearts not complicated
5 pairs of aortic arches pump blood into dorsal and vetral blood vessels. Dorsal blood vessels carry blood to the front of the earthworm
- dont have kidneys but have nephridia that filter out dead cells and other waste through the anus
How do earthworms move ?
1) they grip the soil with some of the back setae so its back part cant move
2) squeezes circular muscles which makes the body longer, then front of body moves forward while back stays still
3) front setae grips back lets go
4) front squeezes longitudinal muscles makes body shorter back moves forward
What are the setae of an earthworm ?
Every segment of the earthworms body except the first and last has four pairs of these tiny, stiff hair like bristle projections
Explain earthworm feeding behaviour
a lip like extension(prostomium) over the mouth helps direct food into the mouth, where a muscular pharynx(segments 1-6) grabs it, coats it with saliva and pushes it down the oesophagus(segments 6-13) into the crop where it is stored temporarily before moving on to the gizzard
Where it gets crushed and ground before moving into the intestines(2/3s of body length) where it gets broken down further by digestive enzyme and gets absorbed into the blood stream.
Left over soil particles and undigested organic matter pass out the worm through the anus in the form of castings
earthworms and their gut microbes process nitrogen compounds to make nitrate and enriches the soil
Explain earthworm reproduction
-Earthworms are hermaphrodites, so each individual has both female and male organs.
-A mature earthworm possesses a clitellum(belt-like swelling) that forms part of its reproductive system containing both male and female reproductive organs
-Even though each earth worm possesses both sex organs they can not fertilise themselves.
-Copulation happens at night where sperm from both are deposited in the other
- both form a cocoon in its clitellum containing fertilised eggs
- the skin of the clitellum sloughs off forming a cocoon conatining eggs in the soil
- each cocoon produces about 18 earthworms that hatch in 30-75 days
- live for 8 years
Explain how earthworm populations are dependent on the environment
They depend on both the physical(temperature,moisture,aeration and texture) and chemical properties(PH) if the soil( prefer neutral to slightly acidic) as well as the availability of food and the ability of the species to reproduce and distribute
Less abundant in disturbed soils and typically only active when enough moisture is present
Briefly explain the role of earthworms
-Earthworms can bring physical, chemical and biological changes to the soil profile which effects the habitat and activities of other organisms present in the soil
- recycle dead plant material to compost and improve nutrient availability by pulling organic material deeper into the soil
- by ingesting and digesting organic material to form hummus, nutrients are made available for plants
- their burrowing activity improves soil structure as well as aeration and the drainage ability of soil.
Earthworms are called ecosystem engineers due to their influence in the soil ecosystem name and explain some of the ways they influence this ecosystem
recycling organic plant material - along with bacteria and fungi decompose and recycle organic plant material and leaf litter
increasing nutrient availability happens in two ways:
-incorporating organic materials into the soil by unlocking the nutrients held within dead organisms and plant matter
- earthworms also take nutrients down through the soil profile bringing them in closer contact with plant roots
improving soil structure- burrowing alters physical structure of soil, open up pores within the soil. Improving aeration, water infiltration and enhances root penetration
providing food for predators - act as a food source for many other predators such as birds, moles, hedgehogs, slugs and snails, ect.
