A handout for annelida phylum

1. Phylum AnnelidaPhylum Annelida
The Segmented WormsThe Segmented Worms
• Annelids are to be
found in marine,
freshwater, and
terrestrial habitats
• The body is vermiform,
bilaterally symmetrical,
and segmented
• The body is triploblastic
with a well developed
coelom

2. Classes of Annelida
• Class Polychaeta (fanworms, clam worms)
• Class Oligochaeta (earthworms)
• Class Hirudinea (Leeches)
• Classes not covered
– Class Branchiobdellida
– Class Acanthobdellida

3. General Characteristics
• Each segment is separated from contiguous ones by a
transverse septum
• The body is covered with a flexible non-chitinous cuticle
• Respiratory gas exchange through skin, gills, or
parapodia
• Most forms have chaeta, hard, bristle-like chitinous
structures
• Excretory system typically consists of a pair of
metanephridia per segment

4. Class - Polychaeta
Feather Duster worms, Clam worms, Christmas Tree worms
• Mostly marine and free-living
• Many chaeta, on fleshy lateral outgrowths of the
body wall known as parapodia
• Well developed head bearing appendages
• Sexes separate, with a free-swimming
trochophore larva
• No clitellum

5. Figure 17.03d

6. Class Oligochaeta
Earthworms and Freshwater Worms
• Are terrestrial with a few freshwater species
• Have few chaeta
• No parapodia
• No distinct head appendages
• Clitellum present
• Hermaphrodites, with copulation required
• Eggs are deposited in a cocoon and development is
direct

8. Earthworm Dissection

9. Figure 17.12c

11. Figure 17.15

13. Class Hirudinea
• Ectoparasites, not all - many feed on organic debris
• Usually dorso-ventrally flattened with fixed number
of body segments (34)
• No chaeta or parapodia
• Clitellum present only during reproduction
• Reproduction similar to earth worms/direct
development
• Two suckers – anterior and posterior

14. Figure 17.20• Coelom
reduced by
invasion of
connective
tissue