PHYLUM MOLLUSCA not drab and mundane as found on the N.A. continent of the eight classes, only 3 are common “MALACOLOGY” The study of molluscs

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 Fig. 16.2

Body Plan Pericardial cavity Metanephridium Mantle cavity Gonad Ctenidium Radula Foot Stomach and digestive gland

Dorsal mantle covers the visceral mass.

Secretes the shell

Ctenidium (Respiration)

Complete digestive system

Paired ventral nerve cords

Radula

Copyright © The McGraw-Hill Companies, Inc Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Radular Structure Source: From A Life of Invertebrates, Copyright © 1979 W. D. Russell-Hunter.

Radula

http://www.wildsingapore.com/chekjawa/pixhtoz/i900b1.gif http://www.personal.dundee.ac.uk/~amjones/radula.jpg

Coelom - metanephridia Skip this diagram

CLASSES

Class Polyplacophora Chitons Fig. 16.1a

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

Class Polyplacophora Stomach Gonad Digestive gland Pericardial cavity Mouth Nephridium 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”

Torsion of body Fig. 16.13

Batton the Hatches! Snails have a trap door called the operculum They can close it to prevent water loss or to avoid being eaten!

Snail Terrestrail Mantle cavity functions as lung

Snail Pneumostome Tentacle (Eye stalks) Shell Anus Tentacle Foot Mouth Genital pore

Internal Structure of a Generalized Gastropod Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Internal Structure of a Generalized Gastropod

Helix – garden snail I’ll get there by midnight, I think…

Nudibranch No shell Dorsal projections Gills Nematocyst discharge

Abalone Several holes in top of shell Excrete waste Food for man

Interesting but don’t write this? Nudibranchs Gastropods that have lost their shell Breathe through their cerata (colorful branches on their dorsal side) Often produce toxic chemicals for protection Or steal undischarged nematocysts taken from their prey.

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 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 radula No eyes, a few species with eyes on mantle margin foot usually wedge-shaped Burrow Sand, wood, rocks

Fig. 16.28b

Fig. 16.26

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 Gooey duct

Bivalves Body is laterally compressed Two shells, hinged together No head, no radula 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 16.31a

Clam Dissection

The Blue Mussel Uses byssal threads to attach to the substrate Threads are secreted by the mussel’s foot Anchors mussel in place on rocks to make filter feeding easier Experimented with as a dental adhesive

Scallops

Shipworms

Class Cephalopoda Squids, 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

http://news. nationalgeographic. com/news/2006/12/061222-giant-squid http://news.nationalgeographic.com/news/2006/12/061222-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

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

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 Died out with dinosaurs 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) Fin Collar Eye

Squid Shell (Pen) Systemic heart Branchial heart Ctenidium Funnel 4

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

Who Wants a Snack? Catches prey with tentacles Suction disks on tentacles used to grasp and hold prey Bite from beak kills prey Poisonous venom in some cases

Squid

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Nautilus Up to 94 tentacles Shell with many chambers No suckers Lives in outermost chamber

Chambered Nautilus

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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

Oysters

Pearl formation Shell Developing pearl Epithelium Irritant lodged between shell and mantle Layers of nacre secreted around foreign material

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