Chapter 27: Mollusks

I. Taxonomy Kingdom: Animalia – Phylum: Mollusca (soft)

II. Characteristics Very diverse phylum (less than 1cm to 20m long!) 2 nd largest phylum with 100,000+ species Soft bodied Internal or external shell Most have TROCHOPHORE: free swimming larvae stage Complex; interrelated organ systems with true coelom Bilateral symmetry Complete digestive tracts

II. Characteristics Body Plan (4 Parts) – A. Foot → could be flat, spade-like or tentacle – B. Mantle → cloak like tissue covering body – C. Shell → IF present, made by glands in mantle (calcium carbonate) – D. Visceral Mass→ internal organs

III. Body Systems A. Digestive – Herbivores, carnivores, filter feeders, detritivores, parasites – Snails/ slugs use RADULA (tongue shaped structures with “teeth” for scraping, drilling, etc) – Octopi- sharp jaws; some have poisons – Clams, oysters, scallops- filter feeders use SIPHON (water enters and leaves) *plankton stick to mucous on gills*

III. Body Systems(cont) B. Respiratory AquaticTerrestrial -Gills- Large mantle cavity lined with BV’s - lining must stay moist

III. Body Systems(cont) C. Circulatory – Open Circ. System Simple heart, Blood vessels- blood in vessels Sinuses (sac), gills, heart slow moving mollusks – Ex) clam, slug, snail

III. Body Systems(cont) Circulatory – Closed Circ. System blood in vessels faster transport Ex) squid, cuttlefish

III. Body Systems(cont) D. Excretory – Nephridia: filter blood; remove waste

III. Body Systems(cont) E. Nervous – - Varies from simple (clams) to complex (octopi) Ex) Octopi – Very intelligent; trainable – Remember information for long periods of time – Can open jars to get food!!

III. Body Systems(cont) F. Movement – Ex) Snails: secrete mucous at base of foot – Ex) Octopi: jet propulsion (water into mantle; out siphon)

III. Body Systems(cont) G. Reproductive – Sexual Many have external fertilization--- larvae Some internal (in female)

IV. Groups of Mollusks A. Kindom: Animalia Phylum: Mollusca Class: Gastropoda – Ex) pond snails, land slugs - shell-less or single shelled - use muscular foot on ventral side to move - many protective features: shells, poison, ink, recycle nematocysts from cnidarians

IV. Groups of Mollusks(cont.) B. Class: Bivalvia (bi-valves) – Ex) clams, oysters, mussels, scallops - two shells held together by muscles - most stay in one place for long period of time (sessile)

IV. Groups of Mollusks(cont.) C. Class: Cephalopoda – Ex) octopi, squid, cuttlefish, nautiluses - soft bodied - head attached to single foot – foot divided into tentacles - tentacles have sucking discs that grab/hold prey - most have small internal shells (cuttlefish – cuttle bone for birds), or no shells at all – complex sense organs: sight and touch – only cephalopod with external shell is nautilus

V. Ecology  Zebra mussels- problem  Many mollusks ‘clean up’ surroundings by filtering algae  Can be used to monitor water quality

Cuttlefish with 2 tentacles and 8 arms

Nautilus