1 ch 13 phylum annelida. 2 phylum annelida “little ring” segmented worms 15,000 species...
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Phylum AnnelidaPhylum Annelida
• “little ring”
• Segmented worms
• 15,000 species– Marine worms
– freshwater worms
– terrestrial worms
– Leeches
• worldwide distribution
• Soft body
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Characteristics of Phylum Characteristics of Phylum AnnelidaAnnelida
• triploblastic– schizocoelomat
e
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Characteristics of Phylum Characteristics of Phylum AnnelidaAnnelida
• Coelom partitioned by walls (septa)
• Serial (repeating) segmentation= metamerism– Each segment= metamere/ somite
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Characteristics of Phylum Characteristics of Phylum AnnelidaAnnelida
SeptaSeptaannuli
• External evidence of septa= circular grooves called annuli (rings)
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Advantages of metamerism1. greater flexibility of movement Movie,
compare to nematode
2. Components organ systems repeated w/i segments
– (repeated excretory, nervous, circulatory structures)
– Built-in redundancy- increases survival
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Note:
• Not all organ systems are metameric
• ie, digestive system extends the length of the organism and is differentiated along its length
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Characteristics of Phylum Characteristics of Phylum AnnelidaAnnelida
• Greater flexibility demands greater fine motor skills– Highly
developed, centralized nervous system
•brain
•Ventral nerve cord
•Ganglion in each metamere
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Movement in Phylum Movement in Phylum AnnelidaAnnelida
• Fluid-filled coelom (except Subclass Hirudinea)= hydrostatic skeleton
• Longitudinal and circular muscles
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Characteristics of Phylum Characteristics of Phylum AnnelidaAnnelida
• Closed circulatory system (except some leeches)– Blood vessels and aortic arches (“hearts”)
– Branch to every metamere
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Excretory System of Excretory System of AnnelidsAnnelids
• 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.
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Phylum Annelida: Phylum Annelida: ClassesClasses
• Class Polychaeta
• Class Clitellata– Sublass Oligochaeta
– Subclass Hirudinea
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• poly = many; chaeta = bristles
• Mostly marine– Example: Neries)
• Mostly dioecious
Class PolychaetaClass Polychaeta
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• Parapodia– fleshy
segmented appendages for locomotion & breathing
• have numerous setae at ends of parapodia
Class Polychaeta (cont’d)Class Polychaeta (cont’d)
Fireworm (Hermodice carunculata)
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• parapodia have numerous setae at ends – Tiny chitinous
bristles
• Chitin= tough, flexible polysaccharide; not soluble in water
– Provide anchorage
– Swimming
Class Polychaeta (cont’d)Class Polychaeta (cont’d)
Fireworm (Hermodice carunculata)
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Class Polychaeta (cont’d)Class Polychaeta (cont’d)
• well differentiated head (prostomium) with specialized organs (eyes, jaws)
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Class Polychaeta (cont’d)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.
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Class Clitellata (cont’d)Class Clitellata (cont’d)
• Clitellum– secretes mucus for cocoon, copulation
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Subclass OligochaetaSubclass Oligochaeta
• oligo = few; chaeta = bristles
• Terrestrial, freshwater, some marine– Example: earthworms, night crawlers
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Subclass Oligochaeta Subclass Oligochaeta (cont’d)(cont’d)
• Prostomium lacks sensory structures
• Parapodia are absent
bioweb.uwlax.edu/.../ earthworm_model_1a.htm
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Subclass Oligochaeta Subclass Oligochaeta (cont’d)(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
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Do these questions Do these questions now…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?
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Subclass Oligochaeta Subclass Oligochaeta (cont’d)(cont’d)
• Gas exchange across moist skin to circulatory system
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Subclass HirudineaSubclass Hirudinea
• Leeches
• Mostly freshwater
• possess clitellum – apparent only during reproduction
• have annelid characteristics but generally lack setae
• Monoecious, cross-fert.
• Generally dorsoventrally flattened
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Subclass Hirudinea Subclass Hirudinea (cont’d)(cont’d)
Locomotion– More complex
muscle system- includes oblique + dorsoventral muscles
– “inchworm” movement via suckers movie
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Subclass Hirudinea Subclass Hirudinea (cont’d)(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
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Subclass Hirudinea Subclass Hirudinea (cont’d)(cont’d)
• Gas exchange across skin (in most)