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Phylum Annelida (segmented worms) I. Main Characteristics • Bilateral Symmetry • Segmented: Body is divided into segments Other Traits - Annelida means “little rings” - body segments separated by septum = internal wall Main Characteristics true coelom (body cavity) Characteristics Cont. • Protostomes –Blastopore develops into mouth • Triploblastic –3 embryonic layers –Ectoderm, Mesoderm, Endoderm II. Characteristics Cont’d Setae-short hair-like bristles that function in locomotion have well-developed nervous system (brain) Ganglia and ventral nerve cord -have closed circulatory system Characteristics Cont. • Excretory System –Nephridia •Filters and collects nitrogenous waste and empties them from the body - sexual reproduction in annelids - some are hermaphrodites 3 Main Annelida Classes 1.Class Polychaeta 2.Class Oligochaeta 3.Class Hirudinea Annelids Include: earthworms marine worms leeches This is a scale worm (Polychaetes). They live 1000 meters below the water’s surface and can turn their mouths inside out. III. Annelid Classes • Class Polychaeta (marine worms) Interesting facts! • Polychaetes are the largest class of annelid worms –5300 species! • Most are between 5 to 10 cm long Class Polychaeta Marine worms -includes: sandworms, bloodworms, fireworms -have paddle-like appendages with setae IV. Class Polychaeta bottom-dwellers Parapodia-lateral extensions of the body Cuticle- protective non-living layer V. Segments • 1st SegmentProstomium –Contains eyes, antennae, etc. • 2nd SegmentPeristomium –Surrounds mouth and bears sensory tentacles VI. Polychaete Feeding • Most carnivorous –Gut is straight tube –Extract nutrition from sediment –Gut has a crop & gizzard • Some can get food by diffusion VII. Other Polychaete Systems Respiration by diffusion Chemoreceptors (help seek out food) Statocysts (detect gravity; if the worm is upside down or not) Nephridia for excretion VIII. Polychaete Reproduction • Mostly separate sexes • Both Asexual and Sexual Reproduction • Asexual reproduction –Budding and Fission • Sexual Reproduction –Most fertilization is external • Can have alternation of generations Nereis Featherduster Fireworm • Class Oligochaeta (Earthworms) Class Oligochaeta – Earthworm -Few setae -Live in soil or fresh water -Castings - enrich soil, (worm poop) Interesting facts! Earthworms may survive being frozen if the freeze is not too rapid Have been kept alive for 6 years, but in the wild probably live two years at the most. IX. Class Oligochaeta • 3000 Species • Mostly freshwater or terrestrial • Clitellum –Used for mucous secretion during copulation and cocoon for mating • Setae: short bristlelike hairs on the outside of the worm’s body. –Function in anchoring and movement Section 27-3 Earthworm Anatomy Anus Setae Body segments Gizzard Crop Dorsal blood vessel Clitellum Mouth Brain Ganglion Circular muscle Longitudinal muscle Nephridia Ganglia Ring vessels Reproductive organs Ventral blood vessel X. Oligochaete Feeding • Complete digestive tract • Path of Food –Mouth pharynx esophagus crop gizzard stomach intestine Oligochaete Feeding • Eat practically everything they come across (anything that will fit into their pharynx) • Sucks a mixture of detrius and soil into its mouth – digests what it can and the rest exits the body through the anus (castings) XI. Other Oligochaete Systems Respiration through moist skin Circulatory System • A “closed system” –2 main blood vessels • Dorsal Longitudinal Vessel • Ventral blood vessel • 5 aortic arches with 10 hearts Nervous System • Primitive with cerebral ganglion (brains) • Nerve cords - run the length of the body. Excretory System • Nephridia- primitive kidneys –Filter and get rid of nitrogenous wastes –Excrete ammonia and urea through nephridiopores Excretory System XII. Oligochaete Reproduction • Hermaphrodites –Sperm transfer between two individuals • Two worms line up anterior to posterior ends • Copulation lasts between 2-3 hours Reproduction Cont. • Cocoon formed –Fertilization occurs here –Clitellum • Some freshwater species asexual Oligochaete Reproduction Class Hirudinea (Leeches) Class Hirudinea -Leeches -external parasites with suckers on each end -medicinal uses (circulation, anti-clotting) Leeches being bred for medical uses. What would you do to cure a swollen foot? XII. Class Hirudinea • Mostly external parasites • No parapodia • Secondary annuli on segments • Circular, longitudinal, and oblique muscle layers XIV. Hirudinean Feeding Two main sources of food: -small invertebrates (snails, etc) -body fluids (blood) Mouth in the anterior sucker Produce “hirudin”- anticoagulent (stops blood from clotting) XV. Other Hirudinean Systems • Gas exchange by diffusion • Sensory Receptors: –Photoreceptors –Can sense temp. XVI. Hirudinean Reproduction • • • • All monoecious All sexually reproducing Clitellum seen during breeding season No larval stages Recap: Taxonomy Kingdom Animalia Phylum Annelida Class Oligochaeta (earthworms) Class Hirudinea (leeches) Class Polychaeta (marine worms) *All are segmented, and have a coelom