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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