1

Ch 13Ch 13Phylum AnnelidaPhylum Annelida

2

Phylum AnnelidaPhylum Annelida

• “little ring”

• Segmented worms

• 15,000 species– Marine worms

– freshwater worms

– terrestrial worms

– Leeches

• worldwide distribution

• Soft body

3

Size of AnnelidsSize of Annelids

• <1mm many meters

Megascolides australis up to 7.5 m!

4Fig. 9.9

5Fig. 9.9

6

Characteristics of Phylum Characteristics of Phylum AnnelidaAnnelida

• triploblastic– schizocoelomat

e

7Fig. 9-13, p188

8

Characteristics of Phylum Characteristics of Phylum AnnelidaAnnelida

• Coelom partitioned by walls (septa)

• Serial (repeating) segmentation= metamerism– Each segment= metamere/ somite

9

Development of Metameric, Coelomic Spaces

10

Characteristics of Phylum Characteristics of Phylum AnnelidaAnnelida

SeptaSeptaannuli

• External evidence of septa= circular grooves called annuli (rings)

11

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

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 Characteristics of Phylum AnnelidaAnnelida

• Greater flexibility demands greater fine motor skills– Highly

developed, centralized nervous system

•brain

•Ventral nerve cord

•Ganglion in each metamere

14

Movement in Phylum Movement in Phylum AnnelidaAnnelida

• Fluid-filled coelom (except Subclass Hirudinea)= hydrostatic skeleton

• Longitudinal and circular muscles

15

Characteristics of Phylum Characteristics of Phylum AnnelidaAnnelida

• Closed circulatory system (except some leeches)– Blood vessels and aortic arches (“hearts”)

– Branch to every metamere

16

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.

17

Phylum Annelida: Phylum Annelida: ClassesClasses

• Class Polychaeta

• Class Clitellata– Sublass Oligochaeta

– Subclass Hirudinea

18

• poly = many; chaeta = bristles

• Mostly marine– Example: Neries)

• Mostly dioecious

Class PolychaetaClass Polychaeta

19

• 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)

20

Class Polychaeta (cont’d)Class Polychaeta (cont’d)

• Gas exchange across parapodia

21

• 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)

22

Class Polychaeta (cont’d)Class Polychaeta (cont’d)

• well differentiated head (prostomium) with specialized organs (eyes, jaws)

23

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.

24

Class ClitellataClass Clitellata

• Earthworms and leeches

• Few/no setae

• Possess clitellum

25

Class Clitellata (cont’d)Class Clitellata (cont’d)

• Clitellum– secretes mucus for cocoon, copulation

26

Class Clitellata (cont’d)Class Clitellata (cont’d)

• monoecious, cross-fertilization

27

Subclass OligochaetaSubclass Oligochaeta

• oligo = few; chaeta = bristles

• Terrestrial, freshwater, some marine– Example: earthworms, night crawlers

28

Subclass Oligochaeta Subclass Oligochaeta (cont’d)(cont’d)

• Prostomium lacks sensory structures

• Parapodia are absent

bioweb.uwlax.edu/.../ earthworm_model_1a.htm

29

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

30

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?

31

Subclass Oligochaeta Subclass Oligochaeta (cont’d)(cont’d)

• Gas exchange across moist skin to circulatory system

32

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

33

Subclass Hirudinea Subclass Hirudinea (cont’d)(cont’d)

• Predatory– Attach to host via 2

suckers

34

Subclass Hirudinea Subclass Hirudinea (cont’d)(cont’d)

Locomotion– More complex

muscle system- includes oblique + dorsoventral muscles

– “inchworm” movement via suckers movie

35

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

36

Subclass Hirudinea Subclass Hirudinea (cont’d)(cont’d)

• Gas exchange across skin (in most)

37

• squeamish?

38

Medicinal leechMedicinal 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