Transcript PowerPoint 14: Annelida 1

Invertebrate Zoology
Lecture 14: Phylum Annelida, Part 1
Lecture outline
 Phylum Annelida
Diversity/Classification
Phylogeny
Bauplan Basics
Feeding
Diversity/Classification

Class Polychaeta
 Well-developed head
(w/ sensory structures
and mouthparts)
 Parapodia
 Setae (usually on
parapodia)
 Temporary gonads
 Primarily found in
marine environments
Diversity/Classification

Class Clitellata
 Clitellum: pronounced
glandular region with
reproductive function
 Permanent gonads
Diversity/Classification

Class Clitellata
 Subclass Oligochaeta:
earthworms
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Minimally-developed
head (compared with
Polychaeta)
No parapodia
Few setae
Permanent gonads
Primarily in moist,
terrestrial environments
Diversity/Classification

Class Clitellata
 Subclass Hirudinoidea:
leeches
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Posterior sucker
Head: Anterior sucker,
head not well-developed
No parapodia
Usually lack setae
Permanent gonads
Primarily in aquatic and
moist, terrestrial
environments
Phylogeny: Hypothesis 1
Based on body plan & development
 Hypothesis 1:
Annelida cross-section:
Note eucoelom (=coelom) surrounded by
muscles and lined with peritoneum
Phylogeny: Hypothesis 2
Based on molecular data, etc…
Bauplan basics

“Classic” protostome features
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Spiral cleavage of the egg
Determinate cell fate
Mesoderm develops from the 4D cell.
Eucoelom develops via schizocoely
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Solid mass of mesoderm breaks apart to create
the eucoelom
Eucoelom completely lined with mesoderm
Organs surrounded by peritoneum & suspended
by mesenteries.
What is the key functional difference between
the eucoelom and the pseudocoelom?
Annelida cross-section:
Note eucoelom (=coelom) surrounded by
muscles and lined with peritoneum
Bauplan basics

Body segmentation
 Often with repetition of parts
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Example 1: multiple parapodia of Polychaeta
Example 2: Many segments with paired
metanephridia in Oligochaeta
Bauplan basics
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Body segmentation
 Prostomium: anterior-most segment
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Prostomium + peristomium  head
 Pygidium: posterior-most segment
Bauplan basics
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Cuticle: secreted by epidermis
 Made of scleroprotein &
mucopolysaccharides
 No chitin
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Septa: divide coelom
 Polychaeta: Septa sometimes perforated 
fluid movement between segments
 Oligochaeta: Generally complete septa
 Hirudinoidea: No septa
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Coelom reduced to interconnected channels,
space filled in by muscles and connective tissue
Feeding: Class Polychaeta
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Raptorial predators
 Example 1: Family Nereidae
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Prey location
Eversible pharynx with jaws!
Feeding: Class Polychaeta
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Raptorial predators
 Example 2: Family
Glyceridae
 Prey location similar
to Family Nereidae
 Eversible pharynx
 Poison glands at
base of hollow jaws
inject toxins
 Notice harmless
“head”
(=prostomium)
Feeding: Class Polychaeta
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Raptorial predators
 Example 2: Family Glyceridae
Feeding: Class Polychaeta
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Deposit feeders
 Example: Family
Terrebellidae
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Builds/lives within burrow
Extends mucus-covered
tentacles for feeding via
cilia
Moves of food via ciliary
in a temporary groove
Moves larger particles via
muscular action
Retracts tentacles via
muscles if disturbed
Feeding: Class Polychaeta
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Deposit feeders
 Example: Family Terrebellidae
Feeding: Class Polychaeta
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Suspension feeders
 Example 1: Family Sabellidae: feather
duster worms
Feeding: Class Polychaeta
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Suspension feeders
 Example: Family Sabellidae
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Cilia-mucus covered tentacles
Cilia create the current
Particles caught in the mucus of the
pinnules; cilia move the particles along
the pinnules toward the radiole, and into
food groove
Food groove sorts particles
Large particles rejected
Medium particles used for tube building
Small particles ingested
Feeding: Class Polychaeta
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Suspension feeders
 Example 2: Family Chaetopteridae
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Tube-dwelling mucus bag feeder
Feeding: Chaetopterus
Feeding: Class Polychaeta
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Suspension feeders
 Example 2: Family Chaetopteridae
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Secretes a thin mucous bag from specialized
parapodia of segment 12. The posterior end
of the bag is anchored at the ciliated cup.
Fan-like parapodia (segments 14-16)
circulate water through the tube, and the
particles get stuck in the mucus bag
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.
Feeding: Class Polychaeta
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Foregut: food
capture/intake
 Lined with cuticle
 Includes mouth,
pharynx/proboscis,
esophagus
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Midgut: digestion/
absorption
 Stomach (in some)
 Intestine
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Hindgut
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Rectum
Anus (at pygidium)
Family Glyceridae
Feeding: Class Clitellata
Subclass Oligochaeta (earthworm)
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Extract organic nutrients from soil
 Mixing, aeration and drainage
 40 tons/acre of earth moved per year
 Pesticides & plowing under reduce
earthworm populations
Feeding:
Oligochaeta (cont.)
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Mouth & muscular
pharynx
 Expand to suck in
soil
 note pharyngeal
muscles
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Digestive system
 Foregut, midgut
and hindgut as in
Polychaeta
Feeding:
Oligochaeta (cont.)
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Esophagus has
specialized regions
& structures
 Calciferous
glands
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Ca++ regulation
 Crop
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Food storage
 Gizzard
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Grinds food
Feeding:
Oligochaeta (cont.)
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Midgut
Typhosole
 Increased surface area
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Chloragogenous
tissue:
 Intermediate
metabolism
 Storage of glycogen
and lipids
 Role in excretion

Lots of undigested
material is defecated
Feeding: Class Clitellata
Subclass Hirudinoidea (leech)
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Focus: blood
sucking leeches
 Attach by posterior
and anterior suckers
 Many with jaws,
others insert pharynx
 Suck by expanding
digestive tract
Feeding: Class Clitellata
Subclass Hirudinoidea (leech)
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Secretions from
salivary glands
 Hirudin
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prevents blood
coagulation
 Anesthetics
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Prevent detection
 Vasodilators
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Maintain blood flow
 Enzymes
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Aid in penetration
Feeding: Class Clitellata
Subclass Hirudinoidea (leech)
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Digestive system
 Blood storage in lateral
pouches (“crop ceca”)
 Blood is broken down
by symbiotic bacteria,
and then by the leech
digestive system
 The symbiotic bacteria
are inhibitory to other
bacteria