Phylum Annelida 1 Phylum Annelida • “little ring” • Segmented worms • 15,000 species – – – – Marine worms freshwater worms terrestrial worms Leeches • worldwide distribution • Soft body 2 Size of Annelids • <1mm many meters Megascolides australis up to 7.5 m! 3 Fig. 9.9 4 Fig. 9.9 5 Trochophore larva 6 Characteristics of Phylum Annelida • triploblastic – schizocoelomate 7 Fig. 9-13, p188 8 Characteristics of Phylum Annelida • Coelom partitioned by walls (septa) • Serial (repeating) segmentation= metamerism – Each segment= metamere/ somite 9 Development of Metameric, Coelomic Spaces 10 Characteristics of Phylum Annelida • External evidence of septa= circular grooves called annuli (rings) Septa annuli 11 Advantages of metamerism 1. greater flexibility of movement, compare to nematode 2. Components organ systems repeated w/i segments – (repeated excretory, nervous, circulatory structures) – Built-in redundancy- increases survival 12 Note: • Not all organ systems are metameric • ie, digestive system extends the length of the organism and is differentiated along its length 13 Characteristics of Phylum Annelida • Greater flexibility demands greater fine motor skills – Highly developed, centralized nervous system • brain • Ventral nerve cord • Ganglion in each metamere 14 Movement in Phylum Annelida • Fluid-filled coelom (except Subclass Hirudinea) = hydrostatic skeleton • Longitudinal and circular muscles 15 Characteristics of Phylum Annelida • Closed circulatory system (except some leeches) – Blood vessels and aortic arches (“hearts”) – Branch to every metamere 16 Excretory System of Annelids • Consists of paired metanephridia (in most) • Excretory tubes with ciliated funnels that remove waste from the coelomic fluid • open to the outside via excretory pores. 17 Phylum Annelida: Classes • Class Polychaeta • Class Clitellata – Sublass Oligochaeta – Subclass Hirudinea 18 Class Polychaeta • poly = many; chaeta = bristles • Mostly marine – Example: Neries video • Mostly dioecious 19 Class Polychaeta (cont’d) • Parapodia – fleshy segmented appendages for locomotion & breathing • have numerous setae at ends of parapodia 20 Fireworm (Hermodice carunculata) Class Polychaeta (cont’d) • Gas exchange across parapodia 21 Class Polychaeta (cont’d) • parapodia have numerous setae at ends – Tiny chitinous bristles • Chitin= tough, flexible polysaccharide; not soluble in water – Provide anchorage – Swimming 22 Fireworm (Hermodice carunculata) Class Polychaeta (cont’d) • well differentiated head (prostomium) with specialized organs (eyes, jaws) 23 Class Polychaeta (cont’d) • Many are euryhaline (able to tolerate a wide range of salinity conditions). • Live under rocks, coral crevices, abandoned shells. • Serve as the basis for many marine food chains. 24 Class Clitellata • Earthworms and leeches • Few/no setae • Possess clitellum 25 Class Clitellata (cont’d) • Clitellum – secretes mucus for cocoon, copulation 26 Class Clitellata (cont’d) • monoecious, cross-fertilization 27 Subclass Oligochaeta • oligo = few; chaeta = bristles • Terrestrial, freshwater, some marine – Example: earthworms, night crawlers 28 Subclass Oligochaeta (cont’d) • Prostomium lacks sensory structures • Parapodia are absent 29 bioweb.uwlax.edu/.../ earthworm_model_1a.htm Subclass Oligochaeta (cont’d) • Feeds on organic or vegetable matter in soil food – May be as many as 50,000/acre • Earthworms very beneficial in aerating the soil. • capable of recycling up to 18 tons of soil/acre annually 30 Do these questions now… 1. The coelomic cavity of annelids is usually divided by walls called ________ 2. What is metamerism? 3. What are the advantages of metamerism? 4. Is any part of the annelid not metameric? What part? 5. To what class do earthworms and leeches belong? 31 Subclass Oligochaeta (cont’d) • Gas exchange across moist skin to circulatory system 32 Subclass Hirudinea • Leeches • Mostly freshwater • possess clitellum – apparent only during reproduction • have annelid characteristics but generally lack setae • Monoecious, cross-fert. • Generally dorsoventrally flattened 33 Subclass Hirudinea (cont’d) • Predatory – Attach to host via 2 suckers 34 Subclass Hirudinea (cont’d) Locomotion – More complex muscle systemincludes oblique + dorsoventral muscles – “inchworm” movement via suckers 35 Subclass Hirudinea (cont’d) • Have a fixed number of metameres • Internal septa are lacking – coelom functions as a single, large chamber with connective tissue, muscle, and spaces 36 Subclass Hirudinea (cont’d) • Gas exchange across skin (in most) 37 • squeamish? 38 Medicinal leech • Attach via suckers, pierce skin with sharp proboscis. Leeches cure • Proboscis resembles 3 circular saw blades. • Salivary glands secrete local anesthetic and an anti-coagulant. • remove hematomas resulting from surgery 39