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 , ,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

mjones/radula.jpg wa/pixhtoz/i900b1.gif

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 Mantle cavity MouthMouth CtenidiumCtenidium FootFoot AnusAnus

Class Polyplacophora MouthMouth DigestiveglandDigestivegland StomachStomachGonadGonad Pericardial cavity NephridiumNephridium AnusAnus

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

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

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

0060.jpg

0063.jpg

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 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 CO 2 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 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.” 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” Dorsal Ventral Posterior surface Right Left

Squid FinFin ArmArm Funnel (siphon) EyeEye TentacleTentacle CollarCollar

Squid Shell (Pen) CtenidiumCtenidium FunnelFunnel SystemicheartSystemicheart Branchial heart

Squid Male TestisTestis Hectocotylous arm PenisPenis

Squid Female Ovary with eggs Nidamental glands Oviducal gland 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

Pearl formation Developing pearl EpitheliumEpithelium ShellShell 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