Biology 320 Invertebrate Zoology Fall 2005

1. Biology 320Invertebrate ZoologyFall 2005 Chapter 13 – Phylum Annelida Part One

2. Phylum Annelida • Name means “ringed” • Mostly marine, but also freshwater and terrestrial representatives • Size varies greatly • Microscopic – 3 m (giant Australian earthworm) • 12,000 spp. • Segmented • Diverse modes of feeding

3. Body Regions • Three main regions (anterior to posterior) • Prostomium • Head with sensory organs • Peristomium with mouth • Trunk • Majority of body segments • Pygidium • Anus • Some sensory appendages • Have annulations (superficial segments), but also true segments • Internal compartmentalization • Growth zone is located just anterior to pygidium • Segments added posteriorly • Oldest segment is most anterior

4. Some organs / structures are found in every segment • Appendages • Coelomic cavities • Nephridia • Gonads • Other organs are parts of integrated systems • Digestive system • Nervous system • Hemal system • Musculature • Segments are separated transversely by septa • Bilateral coelomic cavities are also partitioned longitudinally by mesenteries

5. Generalized Body Wall • Cuticle • Protective layer that resists abrasion and helps prevent desiccation • Annelids are still restricted to moist environments • Epidermis • Glandular for production of mucus • Previously discussed functions of mucus apply here • Produce chaetae • Chitinous bristles that project from epidermis • Used for traction • Not to be confused with setae of arthropods, which are sensory hairs • Connective tissue • Musculature • Circular and longitudinal

6. Generalized Nervous System • CNS • Brain is located dorsally in prostomium • Two ventral longitudinal nerve cords with giant axons • Impulses travel up to 40X faster than neurons of average diameter • Facilitate the escape response • Segmental ganglia • Commissures give the nervous system a ladder-like appearance • Sensory structures • Typical unicellular receptors distributed on head, body, and appendages • Polychaetes posses eyes and nuchal organs (more later)

7. Coelomic Cavities • Two lateral coelomic cavities in each segment • Transverse septa • Two longitudinal mesenteries • One ventral and one dorsal to gut • Benefit is that musculature and hydrostat of individual segments can be precisely controlled • Coelomic cavities may be lined with mesothelium containing chlorogogen cells • Tissue appears yellow or brown in color • Has important metabolic functions • Synthesis and storage of glycogen and lipids • Detoxification • Hemoglobin synthesis • Protein catabolism and formation of nitrogenous wastes

8. Segmentation • Advantages: • Burrowing • Isolation of hydrostat and muscular contractions • Studies have compared fluid pressures in segmented worms vs. non-segmented worms that are burrowing • Pressure is transmitted throughout coelom in non-segmented • In order to prevent aneurisms, all muscles must contract in order to antagonize pressure

9. Generalized Hemal System • Dorsal and ventral blood vessel, which are connected by capillary beds • Blood is pumped by: • Vessels • Muscular contractions • Enlarged portions of anterior dorsal blood vessel which function as hearts • Blood may contain some hemoglobin, but typically larger concentrations are contained in amoeboid coelomocytes • WBC + RBC hybrid • Gas exchange occurs across body wall, appendages, and gills

10. Generalized Excretory System • Paired segmental nephridia • Funnels or terminal cells project into coelomic fluid • Highly coiled tubule • Large surface area for secretion and absorption • Nephridiopore opens to exterior of animal

11. Generalized Reproduction • Clonal • Fragmentation • Budding • Paratomy • Sexual • Gonochoric • External fertilization • Gametes exit through nephridiopores • Gonads are segmental, and housed in coelomic cavities • Trochophore larvae, with growth zone just anterior to the telotroch

12. Class Polychaeta • Polychaetes or bristleworms • Name means “many chaetae” • 8000 spp. • Marine, a few freshwater, and a few tropical terrestrial varieties • Diverse feeding ecology, locomotion, and chaetae structure • Also abundant (13,425 / m2 in Tampa Bay, FL) • 2 mm to 3 m (Eunice)

13. Body Form • Posses appendages called parapodia • Lateral outgrowths of body wall • Supported by chitinous rod • Each segment bears one pair • Posses a chaetal sac which secretes a bundle of chaetae • Chaetal structure is closely related to lifestyle and locomotion • Errant (motile) • Leg shaped – crawling • Paddle shaped – swimming • Shovel shaped – digging • Sedentary • Reduced – burrowing • Hook shaped – also for burrowing

15. Tubes • Only annelids that secrete and occupy tubes • Constructed from: • Fibrous proteins • Foreign materials • Calcified by animal to form a shell • Tubes may be attached to a surface or partially buried in sediment • Several functions: • Protection • Hide-out from which prey can be ambushed • Brooding chamber • Sometimes tubes wash up on beaches

16. Nervous System • Typical of annelids • Segmental pedal ganglia associated with parapodia • Sensory organs • Nuchal organs • Unique to polychaetes • Pair of eversible ciliated chemosensory pits on prostomium • Ocelli • Best developed in errant varieties, but useful for detecting shadows in sedentary worms • Statocysts • Useful to burrowers • Sensory appendages • Antennae – prostomium • Palps – prostomium • Cirri – peristomium, parapodia, and pygidium

17. Digestive System • Typical of annelids • May have a protrusible pharynx • With jaws for grasping prey • May be used for burrowing • Esophageal ceca secrete digestive enzymes • Many strategies for waste removal, based on lifestyle • Errant – leave wastes behind while moving • Sedentary – interesting adaptations and behaviors to help avoid waste contamination • Some live upside down in burrows • Some invert themselves just while defecating (sensory appendages on pygidium are useful here) • May create unidirectional water flow through the burrow tube

18. Nutrition • Once again, related to lifestyle • Errant • Carnivores often have protrusible pharynx with jaws • Herbivores or scavengers • Burrowers • Deposit feeders • Tube dwellers • Deposit feeders • Sedentary (attached) • Suspension feed using feather crown with large SA • Parasites • Endoparasites of polychaetes and sea stars • Ectoparasites that suck the blood of eels

19. Gas Exchange • Body wall • Gills • Exposed, delicate outgrowths of body surface • Modified portions of parapodia • Feeding crowns in sedentary polychaetes, such as feather-duster worms, double as gills

20. Circulatory System • Smaller varieties lack a hemal system, but possessed by larger animals • Typical annelid system plus lateral parapodial vessels • Variety of oxygen binding pigments can be found, especially in larger animals • All function differently and have different oxygen affinities • Intertidal polychaetes must cope with periods of emersion or stagnation of water • Some undergo torpor – suppress metabolism • Rely on stored oxygen from neuroglobin or myoglobin

21. Excretion • Typically have segmental nephridia • Occasionally localized in one or a few segments • Feather duster worms have one pair of anterior nephridia that empty via one medial nephridiopore, located on the head • Tubes are coiled to increase SA for secretion / absorption • Osmoregulate in low salinity (brackish) water by increasing rate of filtration • Removes excess water • A few species have even colonized freshwater

22. Reproduction • Clonal • All forms of clonal reproduction • Excellent regenerators • Chaetopterus can grow an entire worm from one segment • Sexual • Most only reproduce sexually • Most gonochoric • Gonads are segmental in “abdomen” • Gametes released into coelom • Ripe gametes are shed via nephridiopores or rupture body wall

23. Epitoky • Reproductive phenomenon characteristic of many polychaetes • Worms exhibit two life phases • Atoke – benthic non-reproductive individual, which transforms into an… • Epitoke – pelagic reproductive individual • Epitokes arise from atokes via metamorphosis or budding • Undergo several modifications and essentially become swimming sacs of gametes • Enlargement of eyes, parapodia, and chaetae • Become sexually mature, and gametes ripen

24. Epitokes reach sexual maturity at the same time and swarm • Swim to the surface and release gametes • Many different cues: • Female pheromone release • Light cycles • Lunar cycles • Very predictable patters in some • Some convert back into atokes after spawning; some reproduce once and die • All regulated by hormones

25. Oviposition • Many shed eggs into sea • Some attach gelatinous masses of eggs to substrata • Chimney of tube • Some brood eggs • Retain eggs in tube or burrow • Sac attached to ventral surface of parent

26. Development • Trochophore larvae in most • Growth zone just anterior to telotroch • May pass through trochophore phase in egg before hatching • Some direct development • Life spans • Some live one or two years, and reproduce once (called annuals) • Some live and breed for more than one year (perennial) • Short life spans that progress through several generations in just one year (multiannual)

27. Diversity • Lugworms • Construct L-shaped burrows • Deposit feeders • Arenicola • Bamboo worms • Construct tubes of sand that resemble drinking straws • Deposit feeders • Live upside down in tubes and ingest substrate from below • Clymenella

28. Paddle worms • Paddle-like portions of parapodia are used as gills • Errant – carnivores that hunt prey by crawling around • Eteone tracks prey by following mucus trails • Ragworms • Errant – crawl, burrow, and swim • Eversible, muscular pharynx with jaws • Lots of cephalic sensory structures • Some reach 1.8 m • Nereis

29. Bloodworms • Live in shallow sedimentary burrows • Ambush predators • Capture prey with extremely long eversible pharynx • Have poison glands • Glycera • Scaleworms • Two rows of overlapping scales (resemble fish scales) on dorsal surface • Scales are actually cirri • Aphrodite (sea mouse) • Covered with extremely long chaetae that resembles felt or hair

30. Fireworms • Brightly colored • Resemble caterpillars • Feed on corals and barnacles • Calcified chaetae break off when touched • Causes a painful, burning sensation • Amphinome • Shaggy tube worms • Chimneys of tubes are ornamented with foreign materials collected by the worm • Camouflage for tube • Ambush predators • Diopatra

31. Parchment-tube worm • Chaetopterus • Lives in U-shaped burrow • Filter feeder • Seines plankton with mucus net it creates • Net is rolled into a ball and swallowed • Mucus is bioluminescent to ward of potential predators • Spaghetti worms • Occupy burrows • Parapodia are reduced to grab sides of burrow • Cluster of extensible tentacles • Extend over sediment like active spaghetti • Can be 1 m or more in length • Mucus on tentacles traps particles • Amphitrite

32. Feather-duster worms • Secrete calcareous tubes or construct from foreign materials • Crown of tentacles (known as radioles) • One radiole (most dorsal) is modified and acts as an operculum when crown is withdrawn • Suspension feeders • Beard worms • Also called pogonophorans • 80 spp. • Live deep in ocean; typically near hydrothermal vents • Up to 1.5 m in length • Prostomium bears beard of tentacles • Also live in tubes • No mouth or anus • Symbiotic chemoautotrophic (sulfur oxidizing) bacteria live in modified gut (trophosome)