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Explore the Diverse World of Annelids: An In-Depth Look into Anatomy, Taxonomy, and Reproduction

Discover the fascinating world of Annelida, a diverse phylum with species inhabiting terrestrial, marine, and freshwater environments. Learn about their segmented bodies, coelomate nature, and specialized systems such as respiratory, circulatory, and nervous. Delve into the taxonomy, anatomy, and reproduction of Polychaetes, Oligochaetes, and Hirudinea, including details on setae, clitellum, and unique adaptations like the posterior sucker in leeches. Uncover the secrets of these organisms and their crucial roles in various ecosystems.

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Explore the Diverse World of Annelids: An In-Depth Look into Anatomy, Taxonomy, and Reproduction

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  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.

  3. Phylum Annelida • Ancestral Traits • Coelomate • Lophotrochozoan • Protostome • Closed circulatory system • Cephalization • Derived Traits • Segmentation • Metamerism • Septa • Setae • Bristles • Myelinated neurons Spirobranchus giganteusChristmas tree worm ~ 40K species of annelids

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

  5. Systems (continue) • Excretory- a pair of nephridia per segment. • Respiratory -through skin, some through parapodia; tubeworms have gills. • Circulatory- closed system, use hemoglobin as oxygen carrier. • Nervous- dorsal brain; ventral, double, solid nerve cord, with gangliain each segment. • Endocrine- hormones secreted by nervous system. • Reproductive- • Dioecious in Polychaeta; no special organs, posterior end becomes gonads. • Monoecious in Oligochaeta and Hirudinea; Clitellum.

  6. Annelid Taxonomy • Phylum Annelida (an-nel-i-da) • Class Polychaeta (poly-key-ta) • Nereis-sand worm, Christmas Tree Worm • Class Clitellata • Subclass Oligochaeta (ol-e-go-key-ta) • Lumbricus-earthworm, Tubifex • Subclass Hirudinea (hi-ru-din-e-a) • Hirudo-leech • Earthworm dissection

  7. Annelid Taxomony • Class Polychaeta (many bristles) • most numerous species • marine Hermodice crunculata

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

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

  10. Annelid Phylogeny

  11. Annelid Body Plan Setae

  12. 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/CO3 materials Bispira bunnea sabellid worm

  13. Polychaete Anatomy

  14. Polychaete Anatomy (cross section)

  15. Polychaeta Amphitrite

  16. Polychaeta Lugworm (Arenicola sp)

  17. Polychaeta

  18. Polychaeta

  19. Clade Siboglinidae (Phylum Annelida?) Riftia pachyptila Ridgea sp

  20. Giant tube worms (Vestimentifera) trophosome Riftia pachyptila

  21. Polychaete Reproduction • Dioecious • Trochophore larvae • Some species develop specialized segments containing gametes • Epitokes • Segments are released and gametes burst out

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

  23. Class Oligochaeta

  24. 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 Phylum Annelida

  25. 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 Phylum Annelida

  26. Oligochaete Anatomy

  27. Oligochaete Anatomy

  28. Setae: a.k.a. Bristles

  29. Oligochaete Reproduction

  30. Oligochaete Development • For terrestrial oligochaetes, development is direct without any larval forms • Some aquatic oligochaetes retain a trochophore-like larval stage

  31. Common Terrestrial Oligocheates: Earthworms • Octagonal-tail worm (Dendrobaena octaedra) • Red marsh worm (Lumbricus rubellus) • Dew-worm or nightcrawler (Lumbricus terrestris) • Pink soil worm (Aporrectodea rosea) • Canadian worm (Aporrectodea tuberculata) • Pasture worm (Aporrectodea turgida) • Woodland white worm (Octolasion tyrtaeum) • Redworm (Eisenia fetida )

  32. Quick and Easy Earthworm Morphology Guide Morphology Number & location of GTs and TPs, location & shape of clitellum Ecology Location of burrows Aporrectodea turgida Lumbricus rubellus

  33. Earthworm Dissection Return to taxonomy Cross section

  34. Aquatic Oligocheates

  35. Subclass Hirudinea • Defining characteristics • Posterior sucker • Predominately freshwater, but do occur in all seas and moist soil • Leeches do not burrow or crawl, lack parapods and setae Phylum Annelida

  36. Subclass Hirudinea

  37. 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 Phylum Annelida

  38. Hirudo medicinalis

  39. 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 Phylum Annelida

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