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Mollusks Belong to phylum Mollusca which means “soft” in Latin.

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Presentation on theme: "Mollusks Belong to phylum Mollusca which means “soft” in Latin."— Presentation transcript:

1 Mollusks Belong to phylum Mollusca which means “soft” in Latin.
2. They are soft-bodied animals that usually have an internal or external shell. 3. Includes snails, slugs, clams, squid and octopi. 4. They all share similar developmental stages. -many aquatic mollusks have a larval stage called a trochophore. -annelids also have trochopore larvae indicating the two groups are closely related.

2 Body Plan The body plan of mollusks has four parts: a. Foot- for movement b. Mantle- thin layer of tissue that covers the body. c. Shell- made by glands in the mantle. d. Visceral mass- consists of internal organs. Feeding Mollusks can be herbivores, carnivores, filter feeders, detritivores, or parasites. 2. Snails and slugs feed using a flexible, tongue- shaped structure called a radula. -has hundreds of tiny teeth to scrape algae or drill a hole through shells of animals to eat the prey’s soft tissue.

3 3. Octopi and certain sea slugs use sharp jaws to eat
their prey. -some octopi produce poisons. 4. Shellfish use feathery gills for filter feeding. -food enters with water through a tube called the incurrent siphon. -small food items become trapped in the sticky mucus of the gill. -water exits the shellfish out the excurrent siphon. Respiration Aquatic mollusks breathe using gills inside their mantle cavity. 2. Land snails and slugs must keep their mantle cavity moist so gases can diffuse with the blood stream.

4 Circulation Oxygen and nutrients are carried by a circulatory system. a. can be an open circ. system- blood leaves vessels and empties into a sinus (large saclike space). -work well for slow moving mollusks with low oxygen demand. b. closed circ. system- blood remains in vessels. -more efficient delivery system for faster-moving mollusks like squid and octopi. Excretion 1. Tube-shaped nephridia remove ammonia from the blood and release it outside the body.

5 Response Complexity of the nervous system varies greatly among mollusks. 2. Clams and other two-shelled mollusks just have small ganglia near the mouth, a few nerve cords, and simple sense organs (chem. receptors,eyespots) 3. Octopi and relatives are active, intelligent predators. -they have the most highly dev. nerv. system of all invertebrates. -have highly dev. brains capable of remembering. Movement Snails and slugs secrete mucus and glide across it. Clams burrow with a hatchet-shaped foot.

6 3. Fast moving squid and octopi use jet propulsion.
-water is drawn in mantle cavity and then forced out through a siphon. Reproduction Some mollusks are hermaphrodites. Many snails and two-shelled mollusks release enormous numbers of eggs and sperm into the water. (external fertilization) 3. In tentacled mollusks and some snails fertilization is internal.

7 Groups of Mollusks **Mollusks are divided into several classes according to characteristics of the foot and the shell. Class Gastropoda Snails, slugs, sea hares, limpets, nudibranchs are commonly called gastropods. 2. They are shell-less or single shelled mollusks that move by a muscular foot on the ventral side. 3. Snails can completely withdraw into the shell for protection and seal it with a hard plate. -also prevents evaporation during drought. 4. Sea hares can squirt ink to confuse predators.


9 5. Some nudibranchs have chemicals that make them
taste bad or are poisonous. -their bright colors serve as warnings. Class Bivalvia Bivalves have two shells that are held together by powerful muscles. 2. Includes clams, oysters, mussels, scallops. 3. Can burrow into sand and mud or secrete sticky fibers to attach to rocks. 4. Scallops can move around by clapping their shells together. 5. Filter-feeding bivalves use mucus and cilia on their gills to trap food particles in the water. 6. Irritants can be coated with “mother-of-pearl .”

10 Internal clam anatomy

11 Class Cephalopoda Cephalopods include octopi, squid, cuttlefish, and nautiluses. 2. The head is attached to a foot that divides into many tentacles. 3. Most have small internal shells or no shells at all. 4. The nautilus has an external shell and up to 90 tentacles. -gases can be secreted into the shell to control it’s buoyancy. 5. They have highly developed brains and sense organs.


13 Ecology of Mollusks Mollusks are an important food source for many
organisms including humans. 2. Bivalves form many symbiotic relationships with bacteria and algae. 3. Since bivalves are filter-feeders they can act as environmental monitors by checking their tissues for dangerous pollutants and microorganisms. 4. Snails are being studied as to why they never develop cancer to gain insight into how to fight cancer in humans.

14 Annelids Members of Phylum Annelida are more related to
mollusks than they are to flatworms or roundworms. -have a similar larval stage with mollusks. 2. The name Annelida is Latin for “little ring,” refering to the ringlike appearance of body segments. 3. Their bodies are divided into segments that are separated by internals walls called septa. 4. In many annelids bristles called setae are attached to each segment. 5. They have a true coelom lined with mesoderm. 6. Food passes from mouth to anus (tube-within-a tube)

15 Feeding and Digestion Annelids range from filter feeders to predatory carnivores. 2. Many feed using a pharynx which is a muscular structure which draws in food. 3. In earthworms food then moves to a storage organ called the crop. 4. Food then passes to a solid organ that grinds the food called the gizzard. 5. Food is then passed to and absorbed by the intestine.

16 Circulation 1. Annelids have a closed circ. system.-blood is contained in a network of blood vessels. 2. In earthworms blood circulates through two major blood vessels that run from head to tail. -the dorsal (top) blood vessel moves blood toward the head of the worm. -blood in the ventral (bottom) blood vessel runs from head to tail. 3. Each body segment has a pair of smaller blood vessels called ring vessels that connect the dorsal and ventral vessels. -these supply blood to the internal organs. -five pairs of ring vessels near the anterior end function as hearts by pumping blood.

17 Respiration Aquatic annelids breathe through gills. Land dwelling annelids undergo gas exchange through their skin and bloodstream by diffusion. -suffocate if skin dries out and will drown if submerged under water for too long. Excretion Digestive waste passes out the anus. Cellular waste containing nitrogen is eliminated by small tubes called nephridia. Response Most annelids have a well developed nervous sys. 2. An anterior brain is connected to several nerve cords. 3. Marine annelids can have many sense organs.

18 Movement Annelids have two major groups of muscles that function as part of a hydrostatic skeleton. a. Longitudinal muscles run front to rear and can contract to make the worm shorter and fatter. b. Circular muscles wrap around each segment and can contract to make the worm thinner and longer. 2. Marine annelids have parapodia- paddelike appendages for swimming and crawling. Reproduction Most reproduce sexually. 2. Some use internal external fertilization and have separate sexes.

19 3. Some like earthworms and leeches are
hermphrodites. 4. Two worms attach to each other and exchange sperm and store it in special sacs. -when eggs are ready for fertilization the clitellum secretes a mucus ring into which eggs and sperm are released. -ring slips off worms body and forms a cocoon. -young worms hatch a few weeks later.

20 Groups of Annelids Class Oligochaeta
Oligochaetes include earthworms and their relatives. Their class name means “few hairs” because they typically have only a few setae. 3. Most live in soil or fresh water. 4. Earthworms leave squiggles of mud above ground called castings. -this is the undigested material that has passed through the body and out the anus. 5. Earthworms help enrich and aerate the soil. 6. Earthworms scientific name is Lumbricus terrestris.


22 Class Hirudinea Contains the leeches. Typically external parasites that suck blood of host. Some are carnivores that feed on worms, snails, insects larvae. 4. The posterior sucker is used for attaching to objects and the anterior sucker sucks the blood. 5. Some leeches extend a muscular structure called a proboscis into the host. 6. Others slice into the host with razor sharp jaws. 7. Leeches release a substance that anesthetizes the wound. 8. Leeches are still used for medicinal purposes.

23 Fear factor leech scene
“What are you doing?” “Feeding my pets!”

24 Class Polychaeta Class name means “many hairs.” Marine annelids that have paired, paddlelike appendages tipped with setae. -form brushlike, feathery structures which give this class it’s name. -these setae or bristles can be used for defense, breaking off when touched causing irritation and burning. 3. Examples are sandworms, bloodworm, fireworms.


26 Ecology of Annelids Annelids are important parts of food chains.
Earthworm burrows provide passageways for plant roots and water.

27 Echinoderms Examples: sea stars, sea urchins, sand dollars,
sea cucumbers, sea lilies, feather stars, brittle stars. 2. Belong to phylum Echinodermata which means “spiny skin.” -their skin is stretched over an endoskeleton of hardened plates of calcium carbonate. 3. They live only in the sea. 4. Typically have no anterior or posterior end and lack cephalization. 5. Bodies are two-sided: -oral surface- mouth side -aboral surface- opposite side.

28 6. Most adult echinoderms exhibit five-part radial
symmetry. -the larvae have bilateral symmetry. 7. Echinoderms are more closely related to vertebrates than any other animal phyla. -echinoderms and vertebrates are deuterostomes- the blastopore develops into an anus. -all other animal phyla are protostomes- the blastopore develops into the mouth. -a blastopore is the opening of the blastula—a hollow ball of cells that forms from the zygote. 8. Echinoderms have a unique water-vascular system: -system of internal tubes filled with fluid that carry out respiration, circulation, and movement.

29 -it opens to the outside through a sievelike structure
called the madreporite. -this leads to a ring canal that forms a circle around the mouth of sea stars. -five radial canals extend along each arm from the ring canal. -attached to each radial canal are hundreds of suction-cuplike structures called tube feet. Feeding Sea urchins scrape algae from rocks. Sea lilies use tube feet to capture floating plankton. Sea cucumbers are detritus feeders. Sea stars are carnivores on mollusks:

30 water vascular system

31 -pry open mollusk shell, invert stomach into shell,
release enzymes and digest the mollusk in its own shell. Respiration and Circulation Oxygen, food, and wastes are carried by the water-vascular system. 2. The thin-walled tissue of the tube feet provide the main surface for respiration. Excretion Solid wastes are expelled through the anus. Nitrogen cellular wastes are passed into the water through the thin-walled tube feet.

32 Response Since they have no head, they have no brain. They have a nerve ring that surrounds the mouth. Radial nerves connect the ring with body sections. Have sensory cells that detect light, gravity, etc. Movement Most move using tube feet and thin layers of muscle attached to their endoskeletons. Reproduction Reproduce by external fertilization. Most species have separate sexes.

33 Groups of Echinoderms Sea Urchins and Sand Dollars
They both have large, solid plates that form a box around their internal organs. 2. Most eat large amounts of algae. 3. Sea urchins can have long, sharp spines.

34 Brittle Stars 1. Have slender, flexible arms and can move rapidly. 2. Can easily shed one or more arms when attacked. 3. They are detritivores and filter feeders.

35 Sea Cucumbers Look like warty, moving pickles. Most are detritus feeders sucking up organic matter along the ocean floor.

36 Sea Stars Can regenerate lost arms. Can regenerate into a new animal if the piece contains a portion of the central body part.

37 Sea Lilies and Feather Stars
Filter feeders with long, feathery arms. Oldest class of echinoderms.

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