Mollusks Kingdom Animalia, Phylum Mollusca (means “soft”)

What is a Mollusk? ● Soft body with internal or external shell ● Ex: snails, slugs, clams, squid, and octopi ● Trochophore l arva

● Body plan: ● Foot – takes on many forms ● Mantle – covers the body & secretes shell ● Shell – (present in most) ● Visceral mass – internal organs

General Characteristics Bilaterally symmetrical Triploblastic

General Characteristics Con’t Open circulatory system – Exception is cephalopods have closed circularoty system Radula usually present (tongue) Protostomes

Groups of Mollusks Three major classes of mollusks Gastropoda Bivalvia Cephalopoda

Gastropods “ Stomach Foot” Snails, Slugs, Nudibranchs, Conchs, Whelks, etc. 35,000+ species

Freshwater, Marine, or Terrestrial Shell-less or single-shelled Move by secreting mucous with cilia or use muscular foot

Snail

Slug

Nudibranchs (sea slugs) Check out the nudibranch gallery at nationalgeographicnudibranch gallery at nationalgeographic

Gastropod Anatomy

Torsion “twisted” body – 180 degree rotation of visceral mass – Significance: allows the snail to retract it’s head into the shell first and it’s foot last.

Interesting Facts! Land snails can lift ten times their own weight up a vertical surface (like a wall). Largest Snail = Giant African Land Snail – Can weigh 2 pounds!

Defense from Predators Shells! But what about poor land slugs and nudibranchs? – Land slugs are usually nocturnal – Some nudibranchs prey on cnidarians and recycle their nematocysts – Some sea hares can squirt ink to hide themselves

Gastropod Feeding Most are predators or scavengers Radula: tongue-like organ that scrapes algae or other plant-like material

Radula

Some predatory gastropods have radula modified to pierce prey

Gastropod Respiration Gas exchange occurs in mantle cavity – gills or diffusion Siphon- inhalent tube – Where water enters body

Gastropod Circulation  Have open circulatory system  Blood not contained w/in vessels; instead it washes over the body tissues  Blood acts as a hydrostatic skeleton

Nervous System Nerves concentrated into large ganglia Most ganglia located in head region Simple or complex eyes Osphradia- chemoreceptors that help to detect prey

Excretion  Nephridium- kidneys  Ammonia = primary nitrogenous waste produced in aquatic species  Uric acid = primary nitrogenous waste produced in terrestrial species

Reproduction  Can be monoecious or dioecious  Usually external fertilization where sperm and eggs released into water  Some internal fertilization in snails

Snail Reproduction

Economic Importance Delicious-Escargot Intermediate host for different parasites Snails and slugs can be serious agricultural pests

Class Bivalvia

General Characteristics Includes clams, oysters, mussels, scallops Two shells – Hence “Bi-valvia”

30,000+ species Marine and Freshwater Mostly filter feeders

Interesting Facts! Largest bivalve -734 pounds and 4 long Ocean Quahog can live to be 220 years old!

Bivalve Respiration Incurrent and Excurrent Siphons – Water enters and exits here Gills greatly expanded and cilliated

Circulation Open Circulatory System – Blood not contained w/in vessels – Blood “washes” over body tissues by action of the beating heart

Bivalve Feeding and Digestion Filter feeders – Labial palps filter out food particles – Non-edible particles flushed out through the excurrent siphon

Nervous System Con’t Most sensory organs are located in the margin of the mantle – Have ganglia – Statocysts and Chemoreceptors

Reproduction Mostly Dioecious Gonads located in visceral mass External fertlization

Economic Importance Mmm Tasty! Pearl production – Multi-billion dollar industry

Class Cephalopod

Cephalopods ● octopi, squids, cuttlefish, and nautilus ● soft-bodied, head is attached to foot ● foot is divided into tentacles with sucking disks Use jet propulsion

Cephalopod Shell Nautilius only one with external shell Internal in squid (pen) and cuttlefish (cuttlebone) Absent in octopi

Movement Use siphon for jet propulsion – Squeeze mantle cavity forcefully Sometimes have external “wings” used to help steer

Feeding Active predators – Many hunt at night Food captured by tentacles and brought to mouth Jaws and radula used

Respiration & Circulation Closed circulatory system – 3 Hearts – Blood is contained w/in vessels Respiration through gills High metabolic rate

Nervous System Very large brain Advanced, large eyes Chemoreceptors Chromatophores-pigment cells Some of the smartest animals on the planet

Some display bioluminescence: use ATP to light up squid: brown or black ink

Octopus (creeps on tentacles)

Squid

Reproduction Dioecious Males have testes and packed sperm in spermatophores All larval development occurs in the egg

Economic Importance Yummy food source- calamari Bait

Octopus versus Shark