Mollusks and Segmented Worms Ch 27 Turboblast Version!!!

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

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

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

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=related Octopuses are very intelligent!

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

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

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

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

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

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

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)

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

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

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

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

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

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

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

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/swimming and gas exchange Has distinct head with well-developed sense organs and eyes

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

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