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  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 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  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 Clitellata Subclass 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 Clitellata Subclass 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 Clitellata Subclass Hirudinoidea (leech)  Secretions from salivary glands  Hirudin  prevents blood coagulation  Anesthetics  Prevent detection  Vasodilators  Maintain blood flow  Enzymes  Aid in penetration

Feeding: Class Clitellata Subclass 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