Systematic Adaptations of Phylum - PowerPoint Presentation

Slide1

Systematic Adaptations of Phylum Mollusca

The

Chitons

, Gastropods, Bivalves and CephalopodsSlide2

The molluscs are a diverse group of soft bodied invertebrates

Some varieties of

molluscs produce an external shell (“test” or “valve”)made of calcium carbonateAll molluscs have a fold of skin associated with the dorsal body wall called the Mantle which encloses the Mantle Cavity. The mantle cavity houses the gills, if present.

General CharacteristicsSlide3

Triploblastic (well developed mesoderm)Organ System

level of body organization

True body cavity (eucoelomate) – the coelom is completely bound by mesodermal tissue and lined with peritoneum.Complete gastrulation

– one way digestive tract with a mouth and an anus

Protostomes – the first opening of the gastrula forms the mouthBilateral symmetry

Body Form & DevelopmentSlide4

Molluscs have a unique body plan with 2 general body regions – the Head-Foot

and the

Visceral MassThe Head-Foot, as the name implies, contains the primary sense organs characteristic of cephalization, the mouth and feeding apparatus, and locomotor organsThe Visceral Mass contains the “guts” – the organs associated with digestion, respiration, reproduction, and circulation

Body PlanSlide5

Mollusc

Body PlanSlide6

Varying degrees of cephalization

occur in the

molluscs. Some (particularly the cephalopods, which include squid and octopus) have very well developed eyes.Cephalization

- PhotoreceptionSlide7

Mollusc

Eyes – Scallop and SnailSlide8

Many

molluscs

(notably the gastropods and cephalopods) have tentacles associated with the Head-Foot regionThe tentacles are used for “touch” and “taste”Cephalization

– Chemoreception and tactile

pressoreceptionSlide9

https://www.youtube.com/watch?feature=player_detailpage&v=yE0QqxwyL_8

Octopus Senses and BehaviorSlide10

Most

molluscs

(all gastropods, chitons and cephalopods) have a specialized rasplike feeding organ called a Radula. The radula is a muscular tongue covered with teeth for scraping off food

Feeding apparatusSlide11

Radula

Teeth from a SlugSlide12

Video of a snail eatingNote the antennae, eyes, and mouthNote the texture and movement of the radula

http

://www.youtube.com/watch?v=cEMK3VN8pW8http://www.youtube.com/watch?v=mLVDwlrSq5U

Snail feeding behaviorSlide13

The foot portion of the head-foot region is used for locomotion and varies greatly within the phylumGastropods (“stomach foot”) and

Chitons

have a broad, laterally flattened ventral footPelecypods (“hatchet foot”) have a muscular foot elongated along the dorso-ventral midlineCephalopods (“head foot”) have modified the foot to form a siphon to eject water for propulsion

The Head-Foot & LocomotionSlide14

Snails

https://www.youtube.com/watch?v=pRmChG3Jf_Q

https://www.youtube.com/watch?v=utxH9MH4tOISea Slugshttps://www.youtube.com/watch?NR=1&v=EwpexfYnlDEhttps://www.youtube.com/watch?v=9VL_p2A7DPg

Gastropod LocomotionSlide15

Octopus

https://www.youtube.com/watch?v=rOvhs5icTfg

https://www.youtube.com/watch?v=t-LTWFnGmeg&feature=player_detailpageSquidhttps://www.youtube.com/watch?v=Nf2iRRWH5OIhttps://www.youtube.com/watch?v=EeaMOOnmHAAhttps://www.youtube.com/watch?v=5o-OMa53F1s

Cephalopod LocomotionSlide16

The Visceral Mass contains what we normally think of as the “internal organs”Aquatic forms have Gills for respiration

Gills are enclosed in the Mantle Cavity, and covered by the Mantle. All

molluscs have a mantle and mantle cavitySome terrestrial forms have diminished gills, and perform gas exchange across the moist membranes of the mantle cavityVisceral Mass - RespirationSlide17

Mantle and Mantle Cavity

Chiton

and MusselSlide18

Mantle and Mantle Cavity

Octopus and SquidSlide19

Many molluscs

secrete protein and calcium carbonate from the mantle to create a shell

The shell typically has 3 layers:The periostacum is the outer layer, made of protein secreted by the edge of the mantleThe prismatic layer is the middle layer, made of densely packed prisms of calcium carbonate in a protein matrixThe nacreous layer

is secreted continuously by the surface of the mantle. This layer is what we call

Mother of PearlThe

Mollusc

ShellSlide20

The mechanism of blood circulation variesBivalves have an Open Circulatory System

. Blood pumped by the heart circulates through blood vessels in the gills, but empties into the

coelom where the visceral organs are bathed by blood Cephalopods have a Closed Circulatory System. Blood is circulated through blood vessels, including capillaries, into all body regionsCirculationSlide21

Metabolic wastes and excess water are removed by the kidneys (

metanephridia

)The kidneys open on the inside to the coelom, communicating with the blood, and discharge wastes into the mantle cavityThe ducts of the excretory system are shared by the Reproductive system, providing passageways for sperm and egg to the mantle cavityExcretion & OsmoregulationSlide22

Reproduction:

Trochophore

LarvaeThe larval form of a

mollusc

is called a TrochophoreSee diagrams and descriptions p. 330 in your textbookSlide23

Mollusc Diversity

Mollusca

is one of the most diverse and widespread phyla in the animal kingdom, second only to the arthropodsWe will focus on only a few of the major classes of molluscsPolyplacophora (Chitons)Gastropods (snails and slugs)

Pelecypods

(Bivalves – Clams, Oysters, Mussels & Scallops)Cephalopods (Squid, Nautilus and Octopus)Slide24

Chitons are similar to gastropods in general body form, but lack the degree of cephalization that is characteristic of slugs and snails

Chitons

are flattened in shape, with multiple prominent gills between the mantle and the footAs the name polyplacophora suggests, the shell consists of many platesPolyplacophora - ChitonsSlide25

Polyplacophora

-

ChitonsSlide26

Foot is flattened and tight to the belly (thus “gastro” “pod” – belly foot)Definite cephalization with both eyes and tentacles (for tactile sense and chemoreception)

Slugs – no shell. Snails – single shell

Asymmetrical deposition of calcium carbonate by the mantle causes the shell of snails to coil (see page 335 in text)Gastropoda – Slugs and SnailsSlide27

Gastropods – Snails and SlugsSlide28

See page 334 in the textbookDuring embryonic development, the mantle cavity of gastropods undergoes

torsion

– the mantle twists so that the posterior of the mantle is relocated over the anterior of the head-footTorsion allows the snail to more readily retract the head into the shell for protectionTorsion also positions the excretory openings over the gills. This problem is resolved by bringing water into the mantle cavity from the left and expelling waste water from the rightTorsion in gastropodsSlide29

Due to shell coiling, most snails have the right gill diminished or absent. The whorls of the coiled shell compress the right side of the mantle cavity and visceral mass

Terrestrial forms of both snails and slugs are lacking gills entirely, using the moist skin of the mantle cavity for gas exchange. These forms are called

PulmonatesNudibranchs are slugs with exposed gills (nudi = naked, branch = gill)Gill variations in gastropodsSlide30

Pelecy = hatchet. The pelecypods

are

molluscs with a hatched shaped footPelecypods are bivalves (2 shells). The shell has 2 distinct parts, attached by a hinge ligamentClams, oysters, and mussels are all pelecypodsAll are filter feeders and lack a radulaAll have little or no cephalization (although some have eyes at the rim of the mantle)

Pelecypoda

– The BivalvesSlide31

Pelecypods

- BivalvesSlide32

Many bivalves use their hatchet shaped foot to burrow into the soilThe mantle is organized to form an incurrent siphon and an

excurrent

siphon – which may extend significantly out of the shellWater circulates through the mantle cavity, and ciliary action of the gill surface channels particles of food trapped in the gill mucus to the mouthSee textbook pages 340-342Filter Feeding in the BivalvesSlide33

Bivalve shells have a distinct Umbo, the oldest part – representing the position of the embryonic shell

The two valves of the shell are connected by a protein

hinge ligament. The elasticity of the hinge ligament causes the shell to openA pair of adductor muscles (one anterior and one posterior) contract to close the shellSand particles trapped between the shell and the mantle may be covered with secretions of calcium carbonate, forming a pearl

Bivalve shellsSlide34

Bivalve shells Slide35

Cephalopods – Squid, and OctopusSlide36

True Facts?

True Facts about the Land Snail

https://www.youtube.com/watch?v=VTV23B5gBsQTrue Facts about the Cuttlefishhttps://www.youtube.com/watch?v=GDwOi7HpHtQTrue Facts about the Octopushttps://

www.youtube.com/watch?v=st8-EY71K84Slide37

Cephalopods – Nautilus and Ammonites

https://

www.fossilera.com/fossils-for-sale/ammonite-pendants