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Phylum Mollusca 2nd Largest animal phylum on Earth

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Presentation on theme: "Phylum Mollusca 2nd Largest animal phylum on Earth"— Presentation transcript:

1 Phylum Mollusca 2nd Largest animal phylum on Earth
~150,000 known species Phylum Mollusca snails, slugs, clams, squids, and octopi Latin mollus: “soft” CLIP

2 Some have lost the shell completely.
Almost all habitats Soft-bodied animals, usually with a hard external shell (Calcium containing). Some have lost the shell completely. CLIP

3 Most mollusks are marine, though some inhabit fresh water, and some snails and slugs live on land.
Mollusks are soft-bodied animals, but most are protected by a hard shell of calcium carbonate. Slugs, squids, and octopuses have reduced or lost their shells completely during their evolution.

4 Protostome coelomates -3 main body parts: Foot, Mantle, Visceral Mass
the coelom is reduced and limited to region around heart

5 foot (typically for locomotion), a visceral mass with most of the internal organs, and a mantle.
The mantle, which secretes the shell, drapes over the visceral mass and creates a water-filled chamber, the mantle cavity, with the gills, anus, and excretory pores. Many mollusks feed by using a straplike rasping organ, a radula, to scrape up food.

6 Water intake and output
Body Plan: Foot: -Flat: crawling -Spade-shaped: burrowing -Tentacles: capturing prey Mantle: thin layer of tissue that covers the body. Visceral mass - contains internal organs: Water intake and output

7 Feeding: Can be herbivores, carnivores, filter feeders, detritivores, or parasites.

8 Respiration: Aquatic-Gills through diffusion Blue hemocyanin, not hemoglobin, is respiratory pigment Has copper instead of iron Land- mantal cavity lined with blood vessals- diffusion Must be kept moist

9 Circulation: Open circulatory system with blood-filled spaces called hemocoels a heart pumps hemolymph through vessels into a hemocoel

10 Excretion: nephridia Movement: Mucus Jet propulsion rapid clapping of valves releases water in spurts

11 Reproduction: Sexual- -external fertilization (Snails) - internal fertilization (tentacled) - hermaphrodites


13 Four main classes: 1-Polyplacophore Chitons are marine animals with oval shapes and shells divided into eight dorsal plates. Chitons use their muscular foot to grip the rocky substrate tightly and to creep slowly over the rock surface. Chitons are grazers that use their radulas to scrape and ingest algae.

14 2 -Bivalva: clams, scallops, mussels
Have 2 shells held together by adductor muscles that close the shell tightly to protect the animal. Feed by filtering small particles from the water sedentary, attached to hard surface foot used for digging in sand

15 Mantle cavity contains gills -feeding and gas exchange. Filter feeders
Cilia convey the particles to the mouth. Water flows into mantle cavity via the incurrent siphon, passes over the gills, and exits via the excurrent siphon. Sexes are separate; the gonad is located around coils of intestine

16 Most bivalves live rather sedentary lives.
Sessile mussels secrete strong threads that tether them to rocks, docks, boats, and the shells of other animals. Clams can pull themselves into the sand or mud, using the muscular foot as an anchor. Scallops can swim in short bursts to avoid predators by flapping their shells and jetting water out their mantle cavity.

17 3-Gastropoda: “univalves”: snails and slugs -Greek gaster: “stomach”
-Single shell in snails -Can close “door” if threatened Move by muscular contractions of the single foot Slugs have either a reduced shell or no shell at all Use a radula for feeding

18 3-Gastropoda: Most are marine, but there are also many freshwater or terrestrial species. In place of the gills found in most aquatic gastropods, the lining of the mantle cavity of terrestrial snails functions as a lung. respiratory pores Aquatic gastropod gills are in the mantle cavity

19 Land snails are hermaphroditic.
a. In pre-mating behavior, they meet and shoot calcareous darts into each other's body wall.  b. Each inserts a penis into the other's vagina; this provides sperm for future fertilization. c. Eggs are deposited in soil and development proceeds without formation of a larvae.

20 Hermaphroditism assures that any two animals can mate-very useful in slow-moving animals

21 Some species are predators.
Radula is modified to bore holes in the shells of other organisms or to tear apart tough animal tissues. The tropical marine cone snails, teeth on the radula form separate poison darts, which penetrate and stun their prey, including fishes.

22 4- Cephalopoda: “head-foot mollusks”: cuttlefish, squids and octopuses
Giant squid can reach 4400 lbs.!! -Very active and can be fast swimmers -reduced shell or no shell -tentacles are modified foot -move by “jet propulsion” -Can have large eye

23 Cephalopods use rapid movements to dart toward their prey which they capture with several long tentacles. Squids and octopuses use beaklike jaws to bite their prey and then inject poison to immobilize the victim. A mantle covers the visceral mass, but the shell is reduced and internal in squids, missing in many octopuses, and exists externally only in nautiluses.

24 Squids and octopuses possess ink sacs; they squirt a cloud of ink to escape predators.

25 A squid has three hearts, one pumps blood to internal organs; two pump blood to gills

26 Octopuses and squids move by "jet propulsion", sucking water into a muscular sac in the mantle cavity surrounding their bodies and quickly expelling it out a narrow excurrect siphon. Cephalopods have an active, predaceous lifestyle Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

27 Squid- Pen


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