PHYLUM MOLLUSCA MALACOLOGY not drab and mundane as

PHYLUM MOLLUSCA • “MALACOLOGY” • not drab and mundane as found on • The study of the N. A. continent molluscs • 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

Radula

http: //www. wildsingapore. com/chekja wa/pixhtoz/i 900 b 1. gif http: //www. personal. dundee. ac. uk/~a mjones/radula. jpg

CLASSES

Class Polyplacophora Chitons

Class 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 Mouth Mantle cavity Ctenidium Foot Anus

Chitons

Class 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

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Nudibranch • No shell • Dorsal projections – Gills – Nematocyst discharge

Abalone • 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

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Class Bivalvia Clams, Oysters, Shipworms

Class Bivalvia • No eyes, a few • Two shells species with eyes on • shell has two lateral mantle margin valves with dorsal hinge • foot usually wedge • Most are filter feeders shaped • No head or radula • Body enclosed in mantle • Burrow – Sand, wood, rocks • Head greatly reduced

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 CO 2 out

• 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 Bivalves

Figure 16. 31 a

Scallops

Shipworms

Class Cephalopoda Squids, Octopuses, Nautiluses

Giant Squid “A live giant squid (Architeuthis) http: //news. nationalgeographic. com/news/2005/09/0927_050927_ giant_squid. html 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. ”

• - 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 contract. (spots to dots) • - octopus crawls and squids swim in schools (jet propulsion) • Marine

Class Cephalopoda • high extinction 10, 000 fossils down to 400 species today • Shell in squid and octopus absent or vestigial • Ink sac • Foot modified into arms and tentacles • All predators

Ammonoids • Extinct • Devonian to Cretaceous – 400 to 65 MYA • Died out with dinosaurs

Squid “you will learn this when we do the dissection” Posterior surface Right Ventral Dorsal Left

Squid Tentacle Arm Funnel (siphon) Collar Eye Fin

Squid Shell (Pen) Systemic heart Branchial heart Ctenidium Funnel

Squid Male Testis Penis Hectocotylous arm

Squid Female Ovary with eggs Oviducal gland Nidamental glands Oviducal 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