Latin for “Little rings” Segmented Worms Phylum Annelida Latin for “Little rings” Segmented Worms

Segmentation Repeating, specialized sections for different purposes or functions Coelom is divided into separate compartments by partitions Septa Enables different compartments to contract or expand independently Duplication of some of the organ systems between each segment provides insurance against injury

Taxonomy Class Polychaeta Class Hirudinea Class Oligochaeta many bristles Class Hirudinea leeches Class Oligochaeta earthworms

Class Polychaeta - “many bristles” Mostly marine worms Have paddle-like appendages on sides “parapodia” Used for movement and respiration Some have bristles to aid in defense

Bristleworm – many setae

Class Polychaeta Have antennae Have specialized mouthparts for feeding Sense the environment Have specialized mouthparts for feeding Jaws (free swimming predators)

Class Polychaeta Some free living Some are sessile E.g. Nereis Predatory Some are sessile live in tubes made of calcium, silica (sand) or protein Filter feeders

Class Hirudinea Smallest class of Annelids (~300 species) Leeches Suck vertebrate blood Carnivorous Powerful suckers at both front and back ends

Leeches No setae or parapodia Classified as a parasite Have suckers at anterior and posterior ends Move by “looping”: Attach anterior sucker then pull rest of body forward Classified as a parasite Secrete an anaesthetic that prevents the host from feeling their presence Secrete an anti-clotting agent If undisturbed, a leech can ingest 10 times its own weight in blood

Class Oligochaeta Earthworms Tubifex (sludgeworm) Found in soil and freshwater Some types are found in the ocean Tubifex (sludgeworm) Can survive in polluted sediments, areas with little oxygen

Oligochaeta anatomy

Oligochaeta anatomy

Movement Requires coordinated movement between the circular and longitudinal muscles To move, the worm: anchors middle segments using setae contracts circular muscles in front of the anchored segments this “squeezes” the fluid in the coelom which in turn causes the worm to “stretch” forward the worm then anchors the anterior end, releases the middle and uses the longitudinal muscles to pull forward the posterior end Made possible by segmentation

Movement

Feeding and Digestion Ingest soil as they burrow Prostomium – flap of skin that covers the mouth when not feeding Mouth – where soil enters the worm Pharynx – muscular region that forces soil through esophagus into the crop Crop – serves as temporary storage Gizzard – muscular “blender” that grinds soil and organic matter

Feeding and Digestion Intestine – long “tube” that absorbs any nutrients in the ground-up soil has a special fold called a Typhlosole increases the surface area of the intestine so that nutrients can be absorbed more efficiently Anus – where any undigested material exits the worm = “worm manure”

Feeding and Ecology Earthworms are decomposers Breakdown organic matter and Release nutrients into soil , thus fertilize it Loosen soil as they burrow and Aerate it (increase its oxygen content)

Feeding and Digestion prostomiumm

Circulation Closed circulatory system transports oxygen, carbon dioxide, nutrients and wastes through the body of the earthworm Ventral and Dorsal blood vessels Blood is forced through blood vessel by contraction of vessels and 5 aortic arches

Circulation

Respiration No specialized respiratory organs Oxygen and Carbon dioxide diffuse directly through skin and into small blood vessels Only if skin is moist

Excretion Nephridia or Nephrostome act like kidneys Nephridiopores remove waste and control water levels in blood Nephridiopores pores on ventral side of worrm release waste and excess water each segment except first three and last one have nephridia and nephridiopores

Excretion

Nervous System Chain of ganglia connected by a ventral nerve cord Most body segments have a single ganglion Have an anterior cerebral ganglia (brain!) Can respond to light, touch, chemicals, moisture, temp, vibrations

Nervous System

Reproduction Hermaphroditic individual worm cannot fertilize own eggs

Reproduction The “Position” head to tail, ventral surface to ventral surface The “Transfer” clitellum secretes mucus each earthworm injects sperm into the mucus mucus moves into pouch-like seminal receptacle of each worm The “Delivery” several days later the worm secretes a tube of mucus and chitin (thick carbohydrate) from clitellum as the worm moves the tube “picks” up eggs and carries it to sperm to be fertilized The “Result” tube closes up to form protective case and 2-3 weeks “baby” worms hatch

Review