Annelida

1. PHYLUM ANNELIDA
(SEGMENTED WORMS)
•ANNELIDA MEANS “LITTLE RINGS” OR “SEGMENTS”
•BILATERALLY SYMMETRICAL COELOMATES
–Coelomes divided into partitions by septa
•INHABIT MARINE, FRESH WATER, & MOIST
ENVIRONMENTS
•HAS COMPLEX DIGESTIVE SYSTEM
•HAS CLOSED CIRCULATORY SYSTEM
•EPIDERMIS IS PRIMARY GAS EXCHANGE ORGAN
•ARE HERMAPHRODITIC
•REPRODUCE SEXUALLY BY CROSS FERTILIZATION
•REPRODUCE ASEXUALLY THROUGH
REGENERATION

2. PHYLUM ANNELIDA
 Body of annelids have segmentation.
Segmentation is a characteristic that
features regularly repeating body
segments.
 Annelids are sometimes called “Bristle
worms”, because of the tiny bristles that
they bear (except leeches) called setae.
 3 Classes

3. CLASS OLIGOCHAETA
• Include earthworms
• Extracts nutrients from soils
• Extremely beneficial to farming as they
enrich and aerate soils

4. EARTHWORM ANATOMY
 Setae project through small pores in the cuticle to
provide anchoring points to allow the earthworm to
move.
 Food is brought in by a muscular pharynx.
 The digestive tract is unsegmented and runs
continuously the length of the body.
 The intestine has a u-shaped fold.

5. DIGESTIVE SYSTEM
Phylum Annelida 5

6. EARTHWORM DIGESTIVE SYSTEM

7. EARTHWORM ANATOMY
 Earthworms also have a crop and a gizzard, which
stores and mechanically digests food.
 Annelids have closed circulatory systems.
 Earthworms have five (aortic arches) hearts.
 The excretory system consists of a pair of nephridia
(similar to our kidneys) in each body segment (except
the first three and last one).

8. EARTHWORM
CIRCULATORY/EXCRETORY SYSTEM

9. EARTHWORM ANATOMY
 The nervous system in earthworms and all
annelids have a pair of cerebral ganglia,
which acts as the brain.
 Earthworms are hermaphrodites and
exchange sperm with each other during
copulation.
 When earthworms mate, they come out of
their burrows at night and touch surfaces.

10. EARTHWORM NERVOUS SYSTEM

11. EARTHWORM REPRODUCTION
 Mating earthworms are held together by
mucus secreted by a reproductive organ called
a clitellum and they are also held together by
setae.
 Sperm are discharged and travel to an opening
called the seminal receptacle.
 After sperm exchange, the worms separate.
 Each worm then secretes a protective covering
over the clitellum that forms a cocoon.

12. EARTHWORM REPRODUCTION
 The cocoon slides forward along the body
 As it slides forward, it passes over the oviducts.
 Eggs from the oviduct and sperm from the
seminal receptacles transfer into the cocoon.
 After fertilization the cocoon slides off the
worm.
 The embryos develop in the cocoon and
eventually emerge as juvenile worms.

13. EARTHWORM REPRODUCTION

14. THE EARTHWORM
Giant Earthworm – Amazon Basin

15. CLASS POLYCHAETA
• Very similar to oligochaeta
• Most are marine
• Have paddle or ridge-like extensions
on segments called parapodia
• Aid in gas exchange and locomotion

16. LUGWORM

17. CLASS HIRUDINEA (LEECHES)
• Most inhabit fresh
water, or moist
terrestrial
environments
• Feed on small
invertebrates or
are parasitic
• Have significant
medicinal value in
treating bruising,
and as a source of
Pharmaceuticals

18. THE LEECH

19. ADAPTIVE RADIATION IN
HIRUDINA
• The parasitic adaptations of the leeches
are: presence of sucking pharynx and a
post-anal sucker, provision for the
secretion of mucus layer over the body by
the skin glands to prevent dehydration,
secretion of an anticoagulant hirudin to
facilitate feeding on blood, and provision
of food storage in the spacious crop. One
full meal by a leech may last it for about
four months.
• Leeches and oligochaetes have a common
ancestry. Leeches are mostly fresh water
animals.
• However, some have become adapted to
terrestrial life (Haemadipsa). Some have