Phylum Annelida: Segmented WormsChapter 27~~~ IN 121

A. General Characteristics Phylum: Annelida1. Annelid: means“tiny rings” 2. Class: Oligochaeta3. Examples: bristleworms, earthworms, leeches.4. Bilateral animals w/ 2 body openings (mouth and anus). 5. Segmented Body6. Live soil or freshwater7. Nocturnal burrowing worm 8. Feeds on dirt filtering out organic matter9. Beneficial to the soil: aeration (opening up soil to allow air to

circulate better), fertilization10. Respiration: oxygen diffuses across moist skin11. Sexual Reproduction- hermaphrodites (Earthworms & Leeches)12. Closed circulatory system: blood contained within vessels, 13. Well Developed Nervous System

B. Earthworm Parts1. Crop: temporary storage sac after mouth2. Gizzard: sac w/muscular walls to grind soil3. Intestine: long intestine stretches length of body

to aid in digestion of soil4. Ganglion: brain-like organ5. Aortic Arches: Heart of worm; really 5 enlarged

blood vessels.

B. Earthworm Parts 6. Anus: wastes are removed7. setae: bristles used for movement located on ventral side 8. Clittelum: enlarged reproductive segment, secretes mucus which helps hold worms together during reproduction

Pathway of Digestion in an Earthworm

1. Prostonium (lip)2. Mouth3. Pharynx (the throat)4. Esophagus5. Crop6. Gizzard7. Intestine8. Anus

C. Leeches:1. Class: Hirudinea2. Parasitic segmented worm3. Most live in fresh water4. Have no bristles for movement, move

w/muscular contractions5. Suckers at each end of body6. Medical Uses

a. Anesthetic b. Increase circulationc. Secretions act as anticoagulants during

feedingsd. Reattachment of digitse. Reduce swellingf. Cosmetic surgery

Segmented Worm Quiz1. The term “annelid” means ___.a. Round worm b. flat worm2. Annelids have ___symmetry and ___ body openings.a. Radial, 1 c. bilateral, 1 b. radial, 2 d. bilateral, 23. True/False: Earthworms have 5 true hearts.4. To keep you from feeling it, the leech secretes an ___

when it bites into you to feed.b. Anesthetic b. toxin c. anticoagulant5. True/False: Leeches serve a useful purpose to man.

Comparing Flatworms, Roundworms, and Annelids

CHARACTERISTICShape

SegmentationBody cavityDigestion and excretion

Respiration

FLATWORMSFlattened

No

Acoelomate

Gastrovascular cavity with one opening only; flame cells remove metabolic wastes

Through skin; no respiratory organs

ROUNDWORMSCylindrical with tapering ends

No

Pseudocoelomate

Tube-within-a-tube digestive tract; opening at each end; metabolic wastes excreted through body wall

Through skin; no respiratory organs

ANNELIDSCylindrical with tapering ends

Yes

Coelomate

Tube-within-a-tube digestive tract; opening at each end; nephridia remove metabolic wastes

Through skin; aquatic annelids breathe through gills

Section 27-3

Compare/Contrast Table

Comparing Flatworms, Roundworms, and Annelids

CHARACTERISTICCirculation

Response

Movement

Reproduction

FLATWORMSNo heart, blood vessels,or blood

Simple brain; nerve cords run length of body; eyespot and other specialized cells that detect stimuli

Gliding, twisting,and turning

Sexual (hermaphrodites); asexual (fission)

ROUNDWORMSNo heart, blood vessels,or blood

Several ganglia in head region; nerve cords run length of body; several types of sense organs

Thrashing

Sexual (primary males and females)

ANNELIDSBlood circulated through blood vessels in closed circulatory system

Well-developed nervous system with brain and several nerve cords; many sense organs

Forward peristaltic movement

Sexual (some are hermaphrodites; some have separate sexes)

Section 27-3Compare/Contrast Table continued