Invertebrate Zoology
Lecture 14: Phylum Annelida, Part 1
Lecture outline Phylum Annelida
Diversity/ClassificationPhylogenyBauplan BasicsFeeding
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 Minimally-developed
head (compared with Polychaeta)
No parapodia Few setae Permanent gonads Primarily in moist,
terrestrial environments
Diversity/Classification Class Clitellata
Subclass Hirudinoidea: leeches 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 1Based on body plan & development
Hypothesis 1:
Annelida cross-section:Note eucoelom (=coelom) surrounded by
muscles and lined with peritoneum
Phylogeny: Hypothesis 2Based on molecular data, etc…
Bauplan basics “Classic” protostome features
Spiral cleavage of the egg Determinate cell fate Mesoderm develops from the 4D cell. Eucoelom develops via schizocoely
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 Example 1: multiple parapodia of Polychaeta Example 2: Many segments with paired
metanephridia in Oligochaeta
Bauplan basics Body segmentation
Prostomium: anterior-most segment Prostomium + peristomium head
Pygidium: posterior-most segment
Bauplan basics Cuticle: secreted by epidermis
Made of scleroprotein & mucopolysaccharides
No chitin
Septa: divide coelom Polychaeta: Septa sometimes perforated
fluid movement between segments Oligochaeta: Generally complete septa Hirudinoidea: No septa
Coelom reduced to interconnected channels, space filled in by muscles and connective tissue
Feeding: Class Polychaeta Raptorial predators
Example 1: Family Nereidae Prey location Eversible pharynx with jaws!
Feeding: Class Polychaeta 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 Raptorial predators
Example 2: Family Glyceridae
Feeding: Class Polychaeta Deposit feeders
Example: Family Terrebellidae 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 Deposit feeders
Example: Family Terrebellidae
Feeding: Class Polychaeta Suspension feeders
Example 1: Family Sabellidae: feather duster worms
Feeding: Class Polychaeta Suspension feeders
Example: Family Sabellidae 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 Suspension feeders
Example 2: Family Chaetopteridae Tube-dwelling mucus bag feeder
Feeding: Chaetopterus
Feeding: Class Polychaeta Suspension feeders
Example 2: Family Chaetopteridae 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 Foregut: food
capture/intake Lined with cuticle Includes mouth,
pharynx/proboscis, esophagus
Midgut: digestion/ absorption
Stomach (in some) Intestine
Hindgut Rectum
Anus (at pygidium)Family Glyceridae
Feeding: Class ClitellataSubclass Oligochaeta (earthworm)
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.) Mouth & muscular
pharynx Expand to suck in
soil note pharyngeal
muscles Digestive system
Foregut, midgut and hindgut as in Polychaeta
Feeding: Oligochaeta (cont.)
Esophagus has specialized regions & structures
Calciferous glands Ca++ regulation
Crop Food storage
Gizzard Grinds food
Feeding: Oligochaeta (cont.)
Midgut Typhosole
Increased surface area Chloragogenous
tissue: Intermediate
metabolism Storage of glycogen
and lipids Role in excretion
Lots of undigested material is defecated
Feeding: Class ClitellataSubclass Hirudinoidea (leech)
Focus: blood sucking leeches
Attach by posterior and anterior suckers
Many with jaws, others insert pharynx
Suck by expanding digestive tract
Feeding: Class ClitellataSubclass Hirudinoidea (leech)
Secretions from salivary glands
Hirudin prevents blood
coagulation Anesthetics
Prevent detection Vasodilators
Maintain blood flow Enzymes
Aid in penetration
Feeding: Class ClitellataSubclass Hirudinoidea (leech)
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