Download Outline 14: Annelida 1

Invertebrate Zoology
Lecture 14: Phylum Annelida, Part 1
I.
Phylum Annelida, Part 1
A.
Diversity/Classification
B.
Phylogeny
C.
Bauplan Basics
D.
Feeding
I.
Diversity/Classification
A.
Class Polychaeta
1.
Well-developed head (w/ sensory structures and mouthparts)
2.
Parapodia
3.
Setae (usually on parapodia)
4.
Temporary gonads
5.
Primarily found in marine environments
B.
Class Clitellata
1.
Features
a)
Clitellum: pronounced glandular region with reproductive function
b)
Permanent gonads
2.
Subclass Oligochaeta: earthworms
a)
Minimally-developed head (compared with Polychaeta)
b)
No parapodia
c)
Few setae
d)
Permanent gonads
e)
Primarily in moist, terrestrial environments
3.
Subclass Hirudinoidea: leeches
a)
Posterior sucker
b)
Head: Anterior sucker, head not well-developed
c)
No parapodia
d)
Usually lack setae
e)
Permanent gonads
f)
Primarily in aquatic and moist, terrestrial environments
Phylogeny
A.
Hypothesis 1: Based on body plan and development
1.
Note eucoelom (=coelom) surrounded by muscles and lined with peritoneum
B.
Hypothesis 2: Based on molecular evidence and other aspects
Bauplan Basics
A.
“Classic” protostome features
1.
Spiral cleavage of the egg
2.
Determinate cell fate
3.
Mesoderm develops from the 4D cell.
4.
Eucoelom develops via schizocoely
a)
Solid mass of mesoderm breaks apart to create the eucoelom
b)
Eucoelom completely lined with mesoderm
c)
Organs surrounded by peritoneum & suspended by mesenteries.
d)
What is the key functional difference between the eucoelom and the
pseudocoelom?
B.
Body segmentation
1.
Often with repetition of parts
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II.
III.
IV.
a)
Example 1: multiple parapodia of Polychaeta
b)
Example 2: Many segments with paired metanephridia in Oligochaeta
2.
Prostomium: anterior-most segment
a)
Prostomium + peristomium  head
3.
Pygidium: posterior-most segment
C.
Cuticle: secreted by epidermis
1.
Made of scleroprotein & mucopolysaccharides
2.
No chitin
D.
Septa: divide coelom
1.
Polychaeta: Septa sometimes perforated  fluid movement between
segments
2.
Oligochaeta: Generally complete septa
3.
Hirudinoidea: No septa
a)
Coelom reduced to interconnected channels, space filled in by
muscles and connective tissue
Feeding/Digestion: Class Polychaeta
A.
Raptorial predators
1.
Example 1: Family Nereidae
a)
Prey location
b)
Eversible pharynx with jaws!
2.
Example 2: Family Glyceridae
a)
Prey location similar to Family Nereidae
b)
Eversible pharynx
c)
Poison glands at base of hollow jaws inject toxins
d)
Notice harmless “head” (=prostomium)
B.
Deposit feeders
1.
Example: Family Terrebellidae
a)
Builds/lives within burrow
b)
Extends mucus-covered tentacles for feeding via cilia
c)
Moves of food via ciliary in a temporary groove
d)
Moves larger particles via muscular action
e)
Retracts tentacles via muscles if disturbed
C.
Suspension feeders
1.
Example 1: Family Sabellidae: feather duster worms
a)
Cilia-mucus covered tentacles
b)
Cilia create the current
c)
Particles caught in the mucus of the pinnules; cilia move the particles
along the pinnules toward the radiole, and into food groove
d)
Food groove sorts particles
e)
Large particles rejected
f)
Medium particles used for tube building
g)
Small particles ingested
2.
Example 2: Family Chaetopteridae: Tube-dwelling mucus bag feeder
a)
Secretes a thin mucous bag from specialized parapodia of segment 12.
The posterior end of the bag is anchored at the ciliated cup.
b)
Fan-like parapodia (segments 14-16) circulate water through the tube,
and the particles get stuck in the mucus bag
c)
When the bag is full of particles, the “ciliated cup”, where the net is
anchored, rolls up the net and it resulting ball is passed along the
ciliated groove to the mouth.
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D.
E.
F.
Digestive system
1.
Foregut: food capture/intake
a)
Lined with cuticle
b)
Includes mouth, pharynx/proboscis, esophagus
2.
Midgut: digestion/ absorption
a)
Stomach (in some)
b)
Intestine
3.
Hindgut
a)
Rectum
b)
Anus (at pygidium)
Class Clitellata, Subclass Oligochaeta (earthworms) (NOTE: Other modes of
feeding exist in this Subclass…)
1.
Oligochaeta feeding:
a)
Feed by taking in soil and extracting organic nutrients from it

Agricultural role: Mixing, aeration and drainage of soil.

40 tons/acre of earth moved per year by earthworms

Pesticides and plowing reduces their populations
b)
Mouth & muscular pharynx: suck in dirt/organic material: note
pharyngeal muscles
2.
Oligochaeta digestive system
a)
Mouth & muscular pharynx: suck in dirt/organic material: note
pharyngeal muscles
b)
Foregut, midgut and hindgut as in Polychaeta
c)
Esophagus has specialized regions & structures

calciferous glands: remove calcium from tissues, acid-base
balance

Crop: storage

Gizzard: grinds food
d)
Typhosole (intestine): increases digestive surface of worm
e)
Chloragogenous tissue: site of intermediate metabolism, storage of
glycogen and lipids, role in excretion
f)
Lots of undigested material is defecated
Class Clitellata, Subclass Hirudinoidea (leeches)
1.
Various modes of feeding: scavenging and predation as well as blood
sucking
2.
Focus on the blood suckers
a)
hang on by posterior and anterior suckers
b)
some with jaws to bite prey, others insert their eversible pharynx
c)
able to suck blood by expanding their digestive tract and creating a
vacuum
d)
Special substances from salivary glands aid in the process

Hirudin: prevents blood coagulation

Anesthetics: keeps host from detecting the leech

Vasodilators: open up blood vessels to maintain flow

In some jawless forms: enzymes to aid in penetration
e)
blood storage in lateral pouches (“crop ceca”)
f)
blood is broken down by symbiotic bacteria, and then by the leech
digestive system
g)
the symbiotic bacteria are inhibitory to other bacteria
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