Annelida Life cycle and body segmentation

Phylum Annelida

1. Phylum Annelida

2. Phylum Annelida
Terrestrial, marine,
freshwater.
Repeating segments.
Triploblastic.
True coelomates – complete
gut.
Closed circulatory system.
Well developed nervous
system.
Respiratory organs.
Protostome development.
Metamerism (unspecialized)
segmentation.
One or more pairs of setae.

4. Phylum Annelida
•Ancestral Traits
–Coelomate
–Lophotrochozoan- non-molting
protostomes
–Protostome
–Closed circulatory system
–Cephalization
•Derived Traits
–Segmentation
•Metamerism
•Septa
–Setae
•Bristles
–Myelinated neurons
~ 40K species of annelids
Spirobranchus giganteus
Christmas tree worm

5. Systems
•IntegumentIntegument- epidermis is one cell layer with mucous gland
that secrete a moist cuticle.
•SkeletalSkeletal -hydrostatic (using coelom)
•MuscleMuscle- longitudinal and circular muscles Each segments
muscles are independent of the other segments.
•DigestiveDigestive- complete, complex, with absorption and
digestive glands and excretory cells.

6. Systems (continue)
•ExcretoryExcretory- a pair of nephridia per segment.
•RespiratoryRespiratory -through skin, some through parapodia; tubeworms
have gills.
•CirculatoryCirculatory- closed system, use hemoglobin as oxygen carrier.
•NervousNervous- dorsal brain; ventral, double, solid nerve cord, with
ganglia in each segment.
•EndocrineEndocrine- hormones secreted by nervous system.
•ReproductiveReproductive-
–Dioecious in Polychaeta; no special organs, posterior end becomes gonads.
–Monoecious in Oligochaeta and Hirudinea; Clitellium.

7. Annelid Taxonomy
•Phylum Annelida (an-nel-i-da)
–Class Polychaeta (poly-key-ta)
•Nereis, Aphrodita, Chaetopterus, Arenicola, Amphitrite
–Class Clitellata
–Subclass Oligochaeta (ol-e-go-key-ta)
•Lumbricus, Tubifex
–Subclass Hirudinea (hi-ru-din-e-a)
•Hirudo, leech
•Earthworm dissection

8. Annelid Taxomony
•Class Polychaeta (many bristles)
–most numerous # species
–marine
Hermodice Hermodice
crunculatacrunculata

9. Annelid Taxomony
•Class Polychaeta
•Class Clitellata
–Subclass Oligochaeta (few bristles)
•Freshwater, marine & terrestrial
Lumbricus terrestris

10. Annelid Taxomony
•Class Polychaeta
•Class Clitellata
–Subclass Oligochaeta
–Subclass Hirudinea
•Fixed # segments (34)
•Setae absent
Hirudo
medicinalis

11. Annelid Phylogeny

12. Annelid Body Plan
Setae

13. Class Polychaeta
•Highly specialized head
regions
–Antennae
–Sensory palps
–Feeding appendages
•Paired extensions of body
(parapodia)
•Often tube-dwelling
–Burrow into substrate and secrete mucus/
CO
3 materials
Bispira bunnea
sabellid worm
Spirobrancheus giganteus

14. Polychaete Anatomy
http://www.telegraph.co.uk/news/picturegalleries/picturesoftheday/
9093134/Pictures-of-the-day-20-February-2012.html

15. Parapodia with setae

16. Polychaete Anatomy (cross section)

17. Polychaeta
Amphitrite

18. Polychaeta
Lugworm (Arenicola sp)

19. Polychaeta

20. Polychaeta
Parchement worm

21. Clade-Siboglinidae

Ridgea sp
Riftia pachyptila

22. Giant tube worms (Vestimentifera)
Riftia pachyptila
trophosome
http://www.bbc.co.uk/nature/life/Polychaete/by/rank/all

23. Polychaete Reproduction
•Most are dioecious-few monoecious
•Some asexually but sexually more common
•Trochophore larvae
•Some species develop specialized
segments containing gametes
–Epitokes
–Segments are released and
gametes burst out

24. Polychaete Asexual Reproduction
•Epitokes are essentially
buds
•Clues to ancestral origin of
segmentation
–Segmentation may have
been derived from
incomplete budding
processes

25. Typosyllis nipponica
Samoan palolo worm 
Palola viridis

26. Class Oligochaeta

27. Phylum Annelida27
Class Oligochaeta
•Defining characteristics
–Pronounced cylindrical
glandular region of the body
= clitellum
•Second largest class in the
phylum Annelida
•Most spp. are earthworms,
very few are marine

28. Phylum Annelida28
Polychaetes and Oligochaetes
•Oligochaetes differ from
polychaetes in several
ways:
–No parapods, fewer setae (if
at all)
–Hermaphroditic with sex
cells produced in a separate
section
–No larval stages
Giant Gippsland earthworm

29. Oligochaete Anatomy

30. Oligochaete Anatomy

31. Setae: a.k.a. Bristles

32. Oligochaete Reproduction

33. Oligochaete Development
•For terrestrial oligochaetes, development is direct without any
larval forms
•Some aquatic oligochaetes retain a trochophore-like larval stage
http://www.naturewatch.ca/english/wormwatch/resources/anatomy.html
Site for earthworm anatomy:

34. Quick and Easy Earthworm Morphology Guide
Aporrectodea turgida
Lumbricus rubellus
-Earthworms can be classified by size,
burrowing habits, and color
-Number, location and pattern of
genital tumescences (GT) and
tubercular pubertatis (TP)
-Location & shape of clitellum

35. Common Terrestrial Oligochaetes: Earthworms
Eisenia foetida
Redworm
Octagonal Tail WormOctagonal Tail Worm
Dendrobaena octaedra
http://www.earthlife.net/inverts/oligochaeta.html
This link shows diversity of Oligochaetes!

36. Earthworm
Dissection
Return to taxonomy
Cross section

37. Aquatic Oligocheates

38. Phylum Annelida38
Subclass Hirudinea
•Defining characteristics
–Posterior sucker
•Predominately freshwater,
but do occur in all seas and
moist soil
•Leeches do not burrow,
lack parapods and setae
•Clitellum only visible
during breeding

39. Horse leech-actually feeds
on small worms
Haemopis sanguisuga
Great Amazon Leech
Haementaria ghiliani

40. Subclass Hirudinea

41. Phylum Annelida41
Leech Anatomy
•Anterior sucker is small
and contains the mouth
–Anterior sucker creates
a wound with saw like
jaws
•Leeches drink other
animals’ blood, usually
vertebrates
–Can be carnivores, or
scavengers; leeches are
not set in their feeding
habits

42. Hirudo medicinalis
More leech info:
http://www.earthlife.net/inverts/hirundinae.html

43. Phylum Annelida44
Leech Reproduction
•Leeches are
simultaneous
hermaphrodites that lack
a free-living larvae stage
•Fertilization is internal
through copulation
•Development occurs in a
cocoon similar to the
Oligochaetes