Annelids – Defining Characteristics Segmented worms Coelomates Trochophore larvae protostome

Segmentation

Annelids – Feeding Filter feeders – use gills to capture food particles from water Others use pharynx to either suck in food or to extend out and get it. Some annelids have jaws on their pharnyx Christmas tree worm 

Nereis – (clam worm) -has jaws for eating and fighting

Respiration Aquatic annelids use gills Earthworm cuticle  Aquatic annelids use gills Terrestrial annelids exchange gases through their skin – their skin must remain moist for this purpose Cuticle on the earthworm helps prevent desiccation Feather-duster worm – gills exposed (red) - tentacles for gathering food

Internal Transport Closed circulatory system Dorsal surface has blood moving toward the head, ventral surface moves blood away from the head Each segment has a ring vessel connecting the ventral with the dorsal Large ring vessels at anterior end act as a “heart” to pump the blood If no heart is present, the bodies muscular contractions move the blood around

Excretion Solid wastes out the anus Metabolic (liquid) wastes are eliminated by nephridia (like the nephrons in our kidneys) 2 nephridia/segment

Response Brain on dorsal surface Nerves travel from the brain, around the gut and a main nerve cord travels down the ventral surface Brain = #11 Ganglia = #12 Ventral Nerve cord = #13

Sense organs Best developed in free living annelids Most of these have sensory tentacles, statocysts, chemoreceptors, and “eyes” Some form images, some are light-detectors Some have sensory organs that detect vibrations (like our tympanic membranes) Spaghetti worm underground With tentacles exposed

Self Defence Burrow into ground or swim away Setae (bristles) anchor worms in the soil Marine fan worms make tubes of CaCO3 to hide in Tube worms 

Self-Defence Marine fireworms have poisonous bristles (burns) Carnivorous annelids have jaws to bite their predators

Movement longitudinal muscles shorten the body Circular muscles contract to decrease the diameter of the worm Coordination of these sets of muscles allow the worms to wiggle, burrow and swim

Reproduction Some reproduce by budding Some have separate sexes and have external fertilization Palolo worms congregate at the surface and release sperm or eggs at the same time Feast for the predators (humans included!)

Earthworms are hermaphrodites and exchange sperm Sperm is stored in sacs until eggs are ready Mucus ring is secreted by the clitellum – sperm and eggs are deposited there and the ring slips off the worm, forming a cocoon for the fertilized eggs

Common Characteristics in all Annelids Unidirectional Digestive System Closed Circulatory System First sign of a ‘heart-like’ structure Nephridia used for excretion Primitive Brains present

Class Polychaeta – bristleworms Mainly marine worm Have padddle-like appendages with bristles Show cephalization

More Polychaetes

Polychaetes

Class Oligochaeta - Earthworms and Relatives Earthworms + Freshwater worms Aquatic – eg tubifex (red, thread-like worms sold for fish food) Oligo – means few (as in few bristles) Castings are excellent fertilizer

Class Hirudinea Commonly known as the LEECHES Fresh and saltwater species (~300) Few land species Muscular proboscis is forced into skin Others slice skin with their jaws

Leeches Hirudin – anti-coagulating chemical is used to keep host’s blood flowing Some also use an aesthetic so the host does not know they are there Used for medicinal purposes

Annelids aerate the soil by burrowing Return nutrients to the soil completing decomposition of material Many annelids are the basis of food chains

Internal Anatomy

Identifying practice: