ANNELIDS

What habitats can annelids inhabit?

• marine

• Freshwater

• Terrestrial

Describe the physiology of an annelid

• body metamerically segmented

• Segments added in front of pygidium

• Some have a set a number

• Body wall with outer circular and inner longitudinal muscle layers

• Outer transparent moist cuticle secreted by epithelium

• Chitin out setae often present on fleshy appendages called parapodia in polychaetes

Describe the morphology of annelids

• nervous system with a double ventral nerve cord and a pair of ganglia with lateral nerves in each metamere

• Brain is a pair of dorsal cerebral ganglia with connectives to cord around esophagus

• Sensory system of tactile organs, taste buds, photoreceptor cells and eyes with lenses

• Hermaphroditic or separate sexes, asexual reproduction by budding in some

• Segments usually divided by septae- which can have their own circulatory system

What are the 3 Classifications of Annelids

1. Polychaeta

2. Oligochaeta

3. Hirudinea

What are the qualities of Polychaeta

• well differentiated head with specialised sense organs

• Pair, paddled like appendages on most segments

• Sexes are separate, hatch into a planktonic larva, which later metamorphoses into a juvenile annelid

Polychaete Life Habits

1. Errant - free moving

2. Sedentary - burrowers

3. Sedentary - tube formers (filter feeders, nutrition from en

How do tube living, deposit-feeding annelids feed?

• ingest up to 120x own weight a day

• Deposit feeding annelids dominate mud bottoms

• Tentacles have respiratory and feeding functions

• The tiny food particles are passed in a mucus band back to the mouth

• Light sensors on tentacles detect shadows - worm pulls tentacles into the tube when threatened

Endosymbiosis relationships with annelids and their environment

• deep sea hydrothermal vents rich in reduced chemicals

• Rifting pachyptila has no gut so it depends for nutrition on chemoautotrophic symbiotic bacteria that pack a large organ called the trophosome

• Haemoglobin in their highly vascularized gill like plumes captures H2S from the vent and CO2 from the water

• Generate organic carbon using sulphide as electron donor and oxygen as an electron acceptor

Qualities of Class Oligochaeta

• terrestrial or freshwater forms

• Most bear setae

• Hermaphrodites

• Citellum from brooding eggs

• Predators, detrivores and direct deposit feeders

Describe the movement in earthworms

• contraction and friction area

Qualities of Class Hirudinea

• leeches, 500 species, mainly freshwater

• Fixed number of segments, usually 34

• Have anterior and posterior suckers

• Coelom does not act as a hydrostatic skeleton

• No septae or setae

• Probably evolved from oligochaete

• Lack parapodia and tentacles

Leech movement

• no setae

• No septae

• Coelom filled with mesenchyme

• Earthworm like peristalsis is impossible

Medicinal use of leeches

• clearing up discoloration of black eyes

• Salina contains anti-inflammatory substances that can relieve symptoms of arthritis

• After surgery for reattachment fo skin flaps for blood flow and promote healing

Digestion in Leeches

• no amylases, lipases or endoproteases

• Only exopeptidases

• Medicinal leech digestion is slow

• 200 days to digest 2-3x its body weight

• No food for up to 18 months

• Blood in gut doesn’t coagulate and continues to flow from wound

How do leeches prevent blood clotting?

• upon injury platelets aggegrate on blood vessel wall to form a haemostatic plug

• Calin inhibits platelet adhesion and decorsin inhibits platelet aggregation

• Cascade of reactions converts prothrombin to thrombin which catalyses conversion of fibrinogen to fibrin

• Hirudin inhibits activation of prothrombin

• Fibrin polymerises and threads weave into the plug to strengthen in

What does leech saliva contain?

• a vosodilator: dilates blood vessels to encourage blood flow

• An anaesthetic: reduces the likelihood the host feels the presence of the leech

• An antibiotic: produced by a symbiont for digestion

Use of leeches for joint pain

80 minutes of treatment gives pain relief within 24h for up to 4 works

Use of leeches after surgery

• after reattaching amputated fingers, leeches drain the blood

• Anticoagulant ensures continued blood flow after leech has dropped off

• Veins eventually re-established naturally