1. Lecture 15: Phylum Annelida, Part 2
Invertebrate Zoology
Lecture 15: Phylum Annelida, Part 2

2. Lecture outline Phylum Annelida, Part 2 Circulation/gas exchange
Osmoregulation/excretion
Nervous system/Sensory structures
Class Polychaeta
Class Clitellata next time…

3. Circulation/gas exchange: Overview
Why do members of Phylum Annelida need a circulatory system?

4. Circulation/gas exchange: Class Polychaeta
Closed circulatory system
Key gas exchange sites
Parapodia
Additional structures (some)
Anterior gills (Terebellidae)
Tentacular crown (Sabellidae)
Body surface
If no other structures

5. Circulation/gas exchange: Class Polychaeta
Two major vessels
Dorsal: blood  anteriorly
Ventral: blood  posteriorly
Extensive capillary beds in
Parapodia
Other gas exchange structures
Anterior and posterior
Intestine
Blood moves between main vessels via
Capillary beds
Segmental vessels (=ring vessel)

6. Circulation/gas exchange: Class Polychaeta

7. Circulation/gas exchange: Class Polychaeta
No hearts
Movement of blood via vessel contraction & body wall contraction
Respiratory pigments
Primarily dissolved within plasma
Primarily hemoglobin
Two forms of hemoglobin for polychaetes in potentially low-oxygen environments
How do these two forms differ? Adaptive value?

8. Circulation/gas exchange: Class Polychaeta
Terrebellidae circulatory system

9. Circulation/gas exchange: Class Clitellata, Subclass Oligochaeta
Closed circulatory system
Organization similar to Polychaeta
Key differences include
Subneural vessel (so 3 main vessels)
More highly-developed pumping structures
Large, muscular dorsal vessel
2-5 pairs of enlarged circumesophageal vessels
One-way valves prevent backflow
Key respiratory surface is the epidermis
Must stay moist. Why? How?

10. Circulation/gas exchange: Class Clitellata, Subclass Oligochaeta

11. Circulation/gas exchange: Class Clitellata, Subclass Hirudinoidea
Combination of the “ancestral annelid” circulatory system & reduced coelomic spaces.
Sometimes reduced coelomic passages only
Blood movement via vessel & body wall contraction

12. Osmoregulation/Excretion Class Polychaeta
Protonephridia or metanephridia (many)
Often associated with coelomoducts
What is it?
Function?
Nephridia and coelomoduct linked in different ways
Osmoregulatory & excretory
Fluid entry  selective reabsorption along tube

13. Osmoregulation/Excretion: Class Clitellata, Subclass Oligochaeta
Metanephridia
Fluid entry
Via coelom
Nephrostome
Via circulatory system
Capillaries
Specialization of regions
Such as..?

14. Osmoregulation/Excretion: Class Clitellata, Subclass Hirudinoidea
Metanephridia
Nephrostome connected to a capsule with amoeboid cells
Function?
Intracellular duct system
Temporary
Formed by coalescing intracellular vacuoles.

15. Nervous System: Class Polychaeta
Dorsal brain within prostomium
What happens if brain is removed?
Anterior sensory structures connect with brain
Often a variety of tentacles, etc…
Circumenteric connectives to ventral nerve cord

16. Nervous System: Class Polychaeta
Paired, fused ventral nerve cords
One ganglion per segment
Lateral nerves  pedal ganglia
Giant axons
Why giant? Function?

17. Nervous System: sensory organs Class Polychaeta
A variety of tactile and chemoreceptors
Anterior nuchal organs
Ciliated pits
Chemosensory
Dorsal cirri of parapodia
Tactile, chemosensory
Also for gas exchange
Photos:

18. Nervous System: sensory organs Class Polychaeta
Photoreceptors
Simple pigment cup (Chaetopteridae)
Pigment cup with lens (Nereidae)
Complex eye with cornea, lens and retina