Mollusks and Segmented Worms

1. Mollusks and Segmented Worms Ch 27 Turboblast Version!!!

2. Mollusks • Phylum: Mollusca (includes slugs, snails, squids, octopus, clams, oysters, cuttlefish) • Slow-moving or jet-propelled • Most mollusks are aquatic, most live in ocean • Some live in fresh water, moist terrestrial habitats • Some sessile (oysters), some swim freely • Some have shells (hard covering), others are adapted to live without hard covering • ALL are bilaterally symmetrical; coelomates, digestive tract with mouth and anus, muscular foot, mantle • Mantle—membrane that surrounds internal organs • In shelled mollusks, mantle secretes the shell

3. How Mollusks feed • Use rasping structure called radula http://www.youtube.com/watch?v=Ipzi9nn5Tfg • Radula—located in the mouth; tonguelike organ with rows of teeth; used to drill, cut, grate, or scrape food • Bivalves lack radulas, they are filter feeders

4. How Mollusks Make Babies • Sexual reproduction, mostly have separate sexes • In most species, release eggs and sperm into water simultaneously, external fertilization • Gastropods on land and few bivalves—hermaphroditic (each individual makes male & female gametes) with internal fertilization http://youtu.be/h0YH4YnS1bo • Developmental stages are similar for all mollusks

5. Nervous Control in Mollusks • Simple nervous systems that coordinate movement and behavior • Some more advanced mollusks have brains (cephalopods demonstrate left/right hemispheres) • Paired eyes ranging in complexity from simple cups to complex eyes • Octopuses’ eyes have irises, pupils and retinas similar to human eyes • http://www.youtube.com/watch?v=GQwJXvlTWDw&feature=relatedOctopuses are very intelligent!

6. Circulation in Mollusks • Well-developed circulation systems with chambered heart (2 or 3 chambers) • Open circulatory system—blood moves through vessels and into open spaces around the body organs • Exposes body organs directly to blood with oxygen and nutrients and removes metabolic wastes • Closed circulatory system—blood moves through the body enclosed entirely in a series of blood vessels; efficient means of gas exchange

7. Respiration in Mollusks • Gills—specialized parts of the mantle consisting of filamentous projections containing rich blood supply for gas transport • Increase surface area through which gases can diffuse • In land snails and slugs, mantle cavity has evolved into primitive lung • Many mollusks have a siphon which expels water and wastes • http://youtu.be/EpUDW1hoBmo

8. How Do Mollusks Excrete (remove metabolic wastes)? • Mollusks use nephridia (similar to kidneys) • Nephridia are organs that remove metabolic wastes, mollusks have one or two which collect wastes from coelom which is located around the heart only • Wastes are discharged into mantle cavity, and expelled from the body by pumping gills

9. Diversity in Mollusca • Phylum Mollusca is divided into 3 classes • Gastropoda (one-shelled mollusks)—stomach-footed mollusks, foot is positioned under the rest of the body • Most have shells (thick or thin), some have none (slugs) • Shelled gastropods: snails, abalones, conches, periwinkles, whelks, limpets, cowries, cones • Occupy freshwater, saltwater, or moist terrestrial habitats • If without shell (slug), body protected by mucus layer • Sea slugs are covered in nematocysts (colorful sea slugs called “nudibranchs”) http://rainsoftottawa.files.wordpress.com/2012/05/nudibranchs2.jpg

10. Diversity of Mollusca • Bivalva (two-shelled or bivalved mollusks)—clams, oysters, scallops • Mostly marine, few in freshwater habitats • No distinct head or radula, use large muscular foot for burrowing into mud or sand • Two shells connected by ligament at hinge • Filter feeders, gill cilia that beat to draw water current through siphon • http://www.youtube.com/watch?v=tFmMS_a7Q9I

11. Diversity in Mollusks • Cephalopoda (Head-footed mollusks)—octopus, squid, cuttlefish, chambered nautilus http://www.youtube.com/watch?v=L8qwRCs_7x0 • Chambered nautilus only one with shell, cuttlefish have reduced internal shell • Most complex structures in cephalopod class • Foot has evolved into tentacles with suckers, hooks, other adhesive structures • Swim/walk over ocean floor in pursuit of prey or in escape, capture prey with tentacles • Radula is beak-like jaw, food is torn and pulled into mouth by radula • Siphons to expel water, can expel forcefully in any direction, helps movement by jet propulsion • FAST! Up to 20 meters per second • Can also use dark ink to evade predators which clouds water • http://www.youtube.com/watch?v=SCgtYWUybIE&feature=fvst • http://www.youtube.com/watch?v=__XA6B41SQQ&feature=related

12. Annelids (Segmented Worms) • Phylum Annelidae (earthworms, leeches, bristleworms) • Bilaterally Symmetrical, coelomates, mouth + anus • Some have larval stages similar larval stages of mollusks (suggesting a common ancestor) • Basic body plan = tube within a tube • Most have tiny bristles called setae (SEE-tee) on each segment (assist in movement by anchoring body to surface that provides leverage) • Found in moist environments (not in polar regions, deserts)

13. Segmentation! • Segmentation provides diversified functions • Bodies divided into ringed segments, segmentation continues internally as each segment is separated from others by partition • Segmentation is important adaptation for movement because each segment has its own muscles that can lengthen and contract individually • Allows for specialization of body tissues and modifications for functions such as sensing and reproduction

14. Nervous System • Simple nervous system, organs and anterior segments modified to sense environment • Some sensory organs sense light • Eyes and retinas are evolved in certain species • Brain in anterior segment in some species • Nerve cords connect brain to nerve centers called ganglia

15. Circulation/Respiration • Closed circulatory system (blood in vessels) • Must live in water or wet areas for gas exchange directly across moist skin

16. Digestion/Excretion • Complete internal digestive tract that runs length of the body • Food/soil taken into mouth and passes across the gizzard • Gizzard—muscular sac and hard particles that helps grind food before it passes into intestine • Undigested material and solid wastes exit through the anus • Two nephridia in almost every segment that collect waste and transport through coelom and out the body

17. Worm Babies • Earthworms and leeches are hermaphrodites • During mating, two worms exchange sperm • Each worm forms capsule for eggs and sperm, eggs are fertilized in capsule, capsule slips off worm and left behind in soil • In 2-3 weeks, young worms emerge from capsule • Bristleworms have separate sexes, reproduce sexually (release eggs, sperm into seawater) • Hatched larvae become part of plankton, once segmentation begins, bristleworms settle to bottom

18. Diversity in Annelids • 3 classes: Oligochaeta (earthworms); Polychaeta (bristleworms, etc.); Hirudinea (leeches) • Chaeta = Bristles

19. Diversity in Annelids • Earthworms—most well-known and easily seen annelids • Only a few setae on each segment, no distinct head • Eat their way through soil, which creates spaces for air and water to pass through soil • Soil passes through digestive system and undigested materials pass out as castings (waste) • Castings of earthworms help fertilize soil

20. Diversity in Annelids • Polychaeta includes bristleworms, fanworms, lug worms, plumed worms, sea mice • Primarily marine animals • Most body segments have many setae (bristles) and a pair of appendages called parapodia used for crawling/swimmingand gas exchange • Has distinct head with well-developed sense organs and eyes

21. Diversity in Annelids • Leeches—segmented worms with flattened bodies, usually no setae • Most live in freshwater streams or rivers • Many species are parasites that suck blood or other body fluids from hosts’ bodies • Attach to host via front and rear suckers • Bites aren’t painful because chemicals in saliva act as anesthetic and anticoagulants • Ingests 2x-5x its body weight per meal, then drops off host • http://www.youtube.com/watch?v=vpv9P1KOVMQ

22. Origins of Mollusks and Segmented Worms • Fossil record shows mollusks were plentiful and diverse as early as 500 mya • Gastropod, bivalve, cephalopod fossils found in Precambrian deposits • Chambered nautilus appears to have changed very little • Annelids likely evolved in the sea, possibly from ancient flatworm larvae • Fossil record of segmented worms is limited because of their soft bodies • Tubes made from polychaetes are most common fossils from Annelidae, dating back to 540 mya