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Mollusks and Annelids Bio II Rupp.

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Presentation on theme: "Mollusks and Annelids Bio II Rupp."— Presentation transcript:

1 Mollusks and Annelids Bio II Rupp

2 Phylum Mollusca Characteristics
Mollusk—from the Latin meaning “soft” Many have hard shells for protection Approx. 112,000 species Range from sedentary feeders to fast moving predators Coelomates Muscles can move without affecting gut Circulatory system is not interfered with Trochophore—larval stage Free-swimming Mouth and anus Cilia for movement and food gathering Annelids and mollusks both have, which shows common ancestry

3 Trochophore Mollusk and annelid larval stage

4 Mollusk Body Plan Two main regions Head-foot Visceral mass
Contains sensory organs in head Foot contains muscle for locomotion Visceral mass Contains heart, digestive organs, excretion organs, and reproduction organs


6 Mollusk Body Plan con’t.
Coelom around heart Mantle covering the visceral mass—aka—epidermal layer Mantle secretes CaCO3 Shells protect, but decrease surface area Gills evolved Gills are protected by mantle cavity Bilateral symmetry—apparent in nervous system Ganglia are connected by nerve cords Light Touch Chemicals

7 Mollusk Body Plan con’t.
Radula Main feeding adaptation Tongue-like strip covered in backwards facing teeth Adapted to mollusk lifestyle Terrestrial snails eat grass Aquatic snails eat algae or drill shells Cone shell has a harpoon-like radula

8 Mollusk Body Plan con’t.
There are 8 classes, we will focus on 3 Gastropoda Bivalvia Cephalopoda

9 Table 37-1 Feature Gastropoda Bivalvia Cephalopoda External shell
One in most species, none in slugs and nudibranchs Two None except chambered nautilus Head Yes No Radula Locomotion Most crawl Most are sessile Rapid swimming

10 Class Gastropoda Gastro means “stomach” and poda means “foot”
90,000 species Snails, abalones, conchs—one shell Slugs and nudibranchs—no shell

11 Class Gastropoda con’t.
Torsion—the twisting process that relocates the mantle cavity Occurs in larval development Places mantle cavity near the head Allows head to be retracted Coiling of the shell is unrelated

12 Class Gastropoda con’t.
Movement occurs by wave-like contractions of the foot Open circulatory system Hemolymph Hemocoel—blood cavity

13 Snails Terrestrial, marine, and freshwater
Eyes on the end of tentacles— they can retreat into head Gill-breathers Land snails have modified gills for gas exchange Need to stay moist Dormancy—mucous plug— prevents desiccation

14 Slugs Respire through modified mantle cavity
Live in moist shady places to prevent desiccation

15 Nudibranchs Marine No shell Name means “naked gill”
Respiration occurs across the entire body Numerous extensions create greater surface area

16 Pteropods Name means “wing foot” Use the foot to swim instead of crawl

17 Class Bivalvia Name means “two shells” Clams, oysters, scallops
Adductor muscles for closing their shells Contraction closes Relaxation opens

18 Class Bivalvia con’t. Each valve or shell has three layers
Thin outer layer to protect against acidity of sea water Thick middle layer of CaCO3 Inner layer has “mother of pearl” coating to create a smooth surface for the soft body

19 Class Bivalvia con’t. Typically sessile Use their foot as an anchor
Fill it with hemolymph to create a hatchet shape Contract foot and pull themselves into the sand

20 Class Bivalvia con’t. Filter feeders No radula No distinct head
Nervous system has three ganglia pairs Mouth Digestive system Foot All are connected Respond to chemicals and touch Some have eyes along mantle—calico scallop

21 Clams Live buried in mud or sand
Mantle cavity is sealed except for the siphons Cilia generate current to pull water in Water exits through excurrent siphon Gills capture organic matter in mucous Gills are also used for gas exchange with hemolymph Typically separate sexes Marine clams use external fertilization Freshwater clams use internal fertilization Sperm in incurrent siphon Larvae exit the excurrent siphon Eventually settle on bottom and mature



24 Oysters Make permanent attachment to hard surface early in life
Commercially grown for food and pearls

25 Scallops Motile Use shells in a clapping motion to swim

26 Teredo or Shipworm Not a filter feeder
Bores into driftwood or boat timbers and ingests the particles Wood is broken down by symbiotic bacteria

27 Class Cephalopoda Name means “head foot”
Octopuses, cuttlefish, squids, chambered nautliluses Foot is concentrated in the head, hence the name Free-swimming

28 Class Cephalopoda con’t.
Predatory lifestyle Circle of tentacles extending from the head Jaws resembling a parrot’s beak Advanced nervous system Largest brain of any invertebrate Divided into lobes Millions of cells Capable of learning and problem solving

29 Class Cephalopoda con’t.
Well developed senses Eyes can form images Tentacles have chemical sensing ability Closed circulatory system Separate sexes Males have specialized tentacles for sperm transfer Females lay and guard eggs No trochophore stage

30 Squids Ten tentacles Two longest tentacles for prey capture, other eight force food into mouth Pump water through excurrent siphon for propulsion Most grow to 1 ft long Giant squid grows to 60 ft

31 Octopuses Eight tentacles Don’t chase prey like squid— crawl and grab
Seldom exceed 3 ft in diameter Pacific octopus can grow to 8 ft in diameter

32 Chambered Nautilus Shell
Series of gas-filled chambers separated by partitions Confined to outermost chamber Gas in the chambers allows buoyancy

33 Cuttlefish

34 Phylum Annelida Characteristics
Name means “little rings” 15,000 species Bilaterally symmetrical Most distinctive feature is the rings True coelom Divided into compartments by partitions Evolutionary advantage— allows different parts to expand and contract independently Duplication of organ systems in each segment—injury insurance Setae and parapodia—allow for division into three classes Oligochaeta Polychaeta Hirudinea

35 Class Oligochaeta Name means “few bristles” Live in soil or freshwater
No parapodia Have a few setae on each segment Most familiar class member is the earthworm

36 Class Polychaeta 2/3’s of annelids Name means “many bristles”
Setae are found on parapodia Antennae and specialized mouth parts Only annelids with trochophore stage Most are marine Some are free-swimming predators and use strong jaws for feeding Others feed on sediment


38 Class Hirudinea 300 species
Live in calm bodies of freshwater or moist vegetation on land No setae or parapodia Each end has a sucker Can crawl using suckers Can swim with undulating motion Carnivorous Invertebrate prey Blood suckers Secrete anesthetic and anticoagulant Can ingest 10x their weight


40 Earthworm Structure and Movement
More than 100 segments Circular and longitudinal muscles Movement Anchor posterior setae Contract circular muscles to extend Anchor anterior setae Contract longitudinal muscles to pull forward

41 Earthworm Feeding and Digestion
Ingest soil while burrowing— use muscular pharynx Soil moves into the crop— temporary storage area Soil is moved from crop to gizzard—a muscular gut that grinds the soil to release the nutrients Nutrients are absorbed by the intestine—typhlosole folds Undigested materials exit through anus Maintains soils fertility by decomposition and aeration

42 Earthworm Circulation
Closed system Blood travels to the posterior through a ventral blood vessel Blood returns to the anterior heart through a dorsal blood vessel Aortic arches link the vessels— these arches act as hearts to contract and move the blood

43 Earthworm Respiration and Excretion
Gases are exchanged by diffusion through skin and cuticle—no specialized organs Diffusion only occurs if skin is moist—mucous and cuticle aid in this effort Cell wastes are eliminated through nephridia Each segment, except, the first three, and last one, have nephridia Coelomic fluid passes through, water is reabsorbed, wastes eliminated

44 Earthworm Nervous System
Chain of ganglia connected by a ventral nerve cord Most segments contain a ganglion Nerves branch from ganglia Several anterior ganglia are fused to form a brain Light Touch Chemicals Moisture Temperature Vibration

45 Earthworm Reproduction
Hermaphrodites that do not self-fertilize Mating Press ventral surfaces together Anterior ends are pointed in opposite directions Held together by mucous and setae at the clitellum Sperm is injected and moves to seminal receptacle Each worm then secretes a tube of mucous and chitin where sperm and eggs meet outside the body 2-3 week development prior to hatching


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