Ch 13 Phylum Annelida 1 Phylum Annelida little

Ch 13 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 • <1 mm many meters Megascolides australis up to 7. 5 m! 3

Fig. 9. 9 4

Fig. 9. 9 5

Characteristics of Phylum Annelida • triploblastic – schizocoelomate 6

Fig. 9 -13, p 188 7

Characteristics of Phylum Annelida • Coelom partitioned by walls (septa) • Serial (repeating) segmentation= metamerism – Each segment= metamere/ somite 8

Development of Metameric, Coelomic Spaces 9

Characteristics of Phylum Annelida • External evidence of septa= circular grooves called annuli (rings) Septa annuli 10

Advantages of metamerism 1. greater flexibility of movement nematode Movie, compare to 2. Components organ systems repeated w/i segments – (repeated excretory, nervous, circulatory structures) – Built-in redundancy- increases survival 11

Note: • Not all organ systems are metameric • ie, digestive system extends the length of the organism and is differentiated along its length 12

Characteristics of Phylum Annelida • Greater flexibility demands greater fine motor skills – Highly developed, centralized nervous system • brain • Ventral nerve cord • Ganglion in each metamere 13

Movement in Phylum Annelida • Fluid-filled coelom (except Subclass Hirudinea) = hydrostatic skeleton • Longitudinal and circular muscles 14

Characteristics of Phylum Annelida • Closed circulatory system (except some leeches) – Blood vessels and aortic arches (“hearts”) – Branch to every metamere 15

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. 16

Phylum Annelida: Classes • Class Polychaeta • Class Clitellata – Sublass Oligochaeta – Subclass Hirudinea 17

Class Polychaeta • poly = many; chaeta = bristles • Mostly marine – Example: Neries) • Mostly dioecious 18

Class Polychaeta (cont’d) • Parapodia – fleshy segmented appendages for locomotion & breathing • have numerous setae at ends of parapodia 19 Fireworm (Hermodice carunculata)

Class Polychaeta (cont’d) • Gas exchange across parapodia 20

Class Polychaeta (cont’d) • parapodia have numerous setae at ends – Tiny chitinous bristles • Chitin= tough, flexible polysaccharide; not soluble in water – Provide anchorage – Swimming 21 Fireworm (Hermodice carunculata)

Class Polychaeta (cont’d) • well differentiated head (prostomium) with specialized organs (eyes, jaws) 22

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. 23

Class Clitellata • Earthworms and leeches • Few/no setae • Possess clitellum 24

Class Clitellata (cont’d) • Clitellum – secretes mucus for cocoon, copulation 25

Class Clitellata (cont’d) • monoecious, cross-fertilization 26

Subclass Oligochaeta • oligo = few; chaeta = bristles • Terrestrial, freshwater, some marine – Example: earthworms, night crawlers 27

Subclass Oligochaeta (cont’d) • Prostomium lacks sensory structures • Parapodia are absent 28 bioweb. uwlax. edu/. . . / earthworm_model_1 a. htm

Subclass Oligochaeta (cont’d) • Feeds on organic or vegetable matter in soil – 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 29

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? 30

Subclass Oligochaeta (cont’d) • Gas exchange across moist skin to circulatory system 31

Subclass Hirudinea • Leeches • Mostly freshwater • possess clitellum – apparent only during reproduction • have annelid characteristics but generally lack setae • Monoecious, cross-fert. • Generally dorsoventrally flattened 32

Subclass Hirudinea (cont’d) • Predatory – Attach to host via 2 suckers 33

Subclass Hirudinea (cont’d) Locomotion – More complex muscle systemincludes oblique + dorsoventral muscles – “inchworm” movement via suckers movie 34

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 35

Subclass Hirudinea (cont’d) • Gas exchange across skin (in most) 36

• squeamish? 37

Medicinal leech • Attach via suckers, pierce skin with sharp proboscis. • Proboscis resembles 3 circular saw blades. • Salivary glands secrete local anesthetic and an anti-coagulant. • remove hematomas resulting from surgery Ch 14 38