PHYLUM MOLLUSCA• “MALACOLOGY”

• The study of molluscs

• not drab and mundane as found on the N.A. continent

• of the eight classes, only 3 are common

Read 147-156

• 50,000 -100,000 living species

• 35,000 extinct species

• Largest = 1000 lbs.

• 80% less than 5 cm

Classes of Mollusca• Class Bivalvia (Clams, oysters)• Class Gastropoda (snails, slugs)• Class Cephalopoda (Squid, octopus)• Class Polyplacophora (Chitons)

• Additional classes not covered– Class Scaphopoda – Class Caudofoveata– Class Solengastres– Class Monoplacophora

Unifying characteristics“INDICATORS OF COMMON ANCESTRY”

• 1. Visceral mass (internal organs) heart, digestion excretion, reproduction

• 2. Mantle- tissue surrounding the visceral cavity, secretes shell (which may be present or absent)

• 3. Muscular foot - organ for propulsion• 4. Head- mouth, sense organs, cerebral

ganglia• 5. Trochophore- juvenile larvae form

• 6. Radula

– Ribbon of small teeth that are used to feed

– Made of chitin

• 7. Siphon

• 8. Gas exchange through gills

• Habitat

– Fresh and salt water and a few terrestrial

Trochophore Larva• All the members of

this phylum start their life as a free living “trochophore”

Generalized Mollusk Anatomy

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Source: From A Life of Invertebrates, Copyright © 1979 W. D. Russell-Hunter.

Radular Structure

Radula

http://www.personal.dundee.ac.uk/~amjones/radula.jpg

http://www.wildsingapore.com/chekjawa/pixhtoz/i900b1.gif

CLASSES

Class PolyplacophoraChitons

Class PolyplacophoraClass Polyplacophora• Eight dorsal plates

• Reduced head

• Radula reinforced with iron

– Scrape algae from rocks

• Multiple gills, along sides of body between foot and mantle edge

Class Polyplacophora

Mantle cavityMantle cavityMantle cavityMantle cavityMouthMouthMouthMouth

CtenidiumCtenidiumCtenidiumCtenidium

FootFootFootFoot

AnusAnusAnusAnus

Chitons

Class GastropodaSnails, Slugs, Conchs, LimpetsClass Gastropoda

Snails, Slugs, Conchs, Limpets

Class Gastropoda• “STOMACH FOOT”• One shell (if present)• single muscular foot • - operculum- trap

door to close for protection

• - radula- scraping tongue

• - can be parasites

-some can have symbiotic relationship with algae "zooxanthellae”

Snail

• Terrestrial

• Mantle cavity functions as lung

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Internal Structure of a Generalized Gastropod

Nudibranch

• No shell• Dorsal projections

– Gills– Nematocyst discharge

AbaloneAbalone

• Several holes in top of shell– Excrete waste

• Food for man

Slug

• No shell• Garden pests

Limpet

• Herbivores• Cling to rocks or other surfaces

Conch

• Large shell• Marine• Many are predators

0060.jpg

0063.jpg

Class BivalviaClams, Oysters, Shipworms

Class BivalviaClams, Oysters, Shipworms

Class Bivalvia• Two shells• shell has two lateral

valves with dorsal hinge• Most are filter feeders• No head or radula• Body enclosed in mantle• Head greatly reduced

• No eyes, a few species with eyes on mantle margin

• foot usually wedge-shaped

• Burrow – Sand, wood, rocks

Giant Clam & Burrowing Clam

Siphon

It’s Like a Straw

• Siphon – tube that sticks out of shell

• Incurrent siphon takes in water carrying food and oxygen

• Excurrent siphon carries water containing wastes and CO2 out

Bivalves• Gills used to obtain oxygen and to filter out small food particles from the water

• Adductor muscles keep shells closed

• As bivalve grows, it adds a layer to its shell

Figure 16.31a

Scallops

Shipworms

Class CephalopodaSquids, Octopuses, Nautiluses

Class CephalopodaSquids, Octopuses, Nautiluses

Giant Squid

“A live giant squid (Architeuthis) measuring roughly 25 feet long attacks a baited fishing line off the Ogasawara Islands. Japanese scientists recently released the first-ever images of a live giant squid in the wild. Many giant squid have washed up on beaches or have been found dead or dying in fishing nets. This specimen was found in New Zealand in 1996.”

http://news.nationalgeographic.com/news/2005/09/0927_050927_giant_squid.html

• - Intelligent and have a complex eye (as in humans) can form images by moving the lens in and out (How do we focus?)

• - chromatophore- pigment sacks with the 3 primary colors. Nerves cause them to expand and contract. (spots to dots)

• - octopus crawls and squids swim in schools (jet propulsion)

• Marine

Class Cephalopoda

• Shell in squid and octopus absent or vestigial

• Ink sac• Foot modified into

arms and tentacles• All predators

•high extinction 10,000 fossils down to 400 species today

Ammonoids

• Extinct• Devonian to

Cretaceous– 400 to 65 MYA

• Died out with dinosaurs

Squid“you will learn this when we do the dissection”

Squid“you will learn this when we do the dissection”

DorsalDorsalVentralVentral

Posterior surfacePosterior surface

RightRight

LeftLeft

SquidSquid

FinFinFinFin

ArmArmArmArm

Funnel (siphon)Funnel (siphon)Funnel (siphon)Funnel (siphon)

EyeEyeEyeEye

TentacleTentacleTentacleTentacle

CollarCollarCollarCollar

SquidSquidShell (Pen)Shell (Pen)Shell (Pen)Shell (Pen)

CtenidiumCtenidiumCtenidiumCtenidium

FunnelFunnelFunnelFunnel

SystemicSystemicheartheartSystemicSystemicheartheart

Branchial heartBranchial heartBranchial heartBranchial heart

Squid MaleSquid MaleTestisTestisTestisTestis

Hectocotylous armHectocotylous armHectocotylous armHectocotylous arm

PenisPenisPenisPenis

Squid FemaleSquid Female

Ovary with eggsOvary with eggsOvary with eggsOvary with eggs

Nidamental glandsNidamental glandsNidamental glandsNidamental glands

Oviducal glandOviducal glandOviducal glandOviducal gland

Oviducal openingOviducal openingOviducal openingOviducal opening

Octopus

• Eight arms with suckers

• Most intelligent invertebrate

Cuttlefish

Nautilus (don’t write just look)

• Up to 94 tentacles– No suckers

• Shell with many chambers– Lives in outermost

chamber

Chambered Nautilus

But They Don’t Have Shells! How do they protect themselves?

• Fast swimmers (jet propulsion)– Force water out the mantle cavity through the siphon.

The siphon can move and point the animal in any direction

• Camouflage: Chromatophores • Ink Cloud • Intelligence• Vision

Economics

• Pearls• Burrowing shipworms • Snails & slugs

– Garden pests– Food– Intermediate hosts for

parasites

Zebra Mussel

• Environmental Pest• Ballast water of ships

from Europe in 1986• Attack be secreting

adhesive byssal threads– Each other– Other mussels– Man made objects

• Pipes, plumbing

Zebra Mussel

• Live in high densities• Feed on

phytoplankton• Reproduce rapidly

Zebra Mussel

• Attach to native mussels

• Killed all native mussels in Lake Erie

Distribution of Zebra Mussel