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