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
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
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
Octopuses 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

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”)

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

11. Diversity in Mollusks
Cephalopoda (Head-footed mollusks)—octopus, squid, cuttlefish, chambered nautilus
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

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/swimming and 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

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