phylum mollusca “malacology” the study of molluscs not drab and mundane as found on the n.a....
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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
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
http://www.personal.dundee.ac.uk/~amjones/radula.jpg
http://www.wildsingapore.com/chekjawa/pixhtoz/i900b1.gif
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
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”
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Internal Structure of a Generalized Gastropod
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
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
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
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
Nautilus (don’t write just look)
• Up to 94 tentacles– No suckers
• Shell with many chambers– Lives in outermost
chamber
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
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