November 3-4, 2014

Phylum Mollusca

Conch

Squid

Nudibranch

Chiton

Clams, Oysters

Octopus

General Characteristics

Soft-bodied invertebratesUnsegmented body, typically bilateral symmetry Internal or external calcium carbonate shell

(usually)Second largest animal phylum

~ 200,000 species Show Cephalization

Sensory organs towards one end of body “head” formation

Habitat/Lifestyle Sessile-mobile Benthic-pelagic Predators-Herbivores-deposit feeders-filter feeders

Typical Body Plan of Mollusks

Three main parts: Foot Mantle Shell

Foot: On ventral side muscular; used for crawling,

burrowing, or capturing prey Can be flat (snails) spade-shaped (clams) or modified into tentacles

(squid and octopus)

Abalone

Body Plan of Mollusks

Body covered with protective mantle: Thin layer of tissue that

covers most of the mollusk’s body

May or may not produce a shell

Shell: made by glands in mantle

that secrete calcium carbonate

Feeding with Radula

Diverse: herbivores, carnivores, filter feeders, detritivores.

Some use Radula for feeding Radula: flexible, tongue-shaped structure covered

with tiny teeth

Herbivores use radula to scrape or cut algae; carnivores use radula to drill through shells or flesh.

Radula

Filter Feeding

Clams, oysters, and scallops filter feed using feathery gills

Mucus produced by gills traps plankton as water comes in through siphons

Mollusc Reproduction & Development

Sexual reproduction, external In tentacled species, fertilization is internal and female

lays fertilized eggs Most have separate sexes that cross-fertilize eggs Some hermaphrodites-both sexesLarval stages Trochophore larva

Free swimming, ciliated, shell formation begins Veliger larva

Free swimming

Zygote

Trochophore

Veliger

Spat

Juvenile

Adult

Respiration

Aquatic species use gills inside mantle to exchange gases

Incurrent and excurrent siphon brings water in

Siphon: Tube-like structure

through which water enters and leaves

Circulation

Can be open or closed circulatory system Open system: blood is pumped by simple

heart into sinuses (large saclike space) then to gills, then back to heart; slower system; found in snails and clams

Closed system: blood is pumped by heart through blood vessels; faster system; found in faster-moving mollusks

6 Classes in Phylum Mollusca

1)Monoplacophora-simple hat shaped shells

2)Polyplacophora----chitons, 8 overlapping shells

3)Scaphopoda-tusk shells

-------------------------------------------------------------------------

4) Gastropoda-snails, slugs, nudibranchs, and conchs, limpets, abalone

4) Bilvalvia - clams, oysters, scallops, and mussels

5) Cephalopoda squid, octopus, and nautilus

Class Gastropoda

“Stomach footed” molluscs

Have a single shell (snails) or no shell (slugs)

Class Gastropoda

NUDIBRANCHS Marine slug Lacks shell

Class Gastropoda

NUDIBRANCHS Feed on sponges Cnidaria,

algae Exposed feathery gills Can be toxic

Retain undigested nematocysts from Cnidaria=Kleptoplasty

Class Bivalvia, Bi-valve = two shells

two-part, hinged shellEx: clams, oysters, scallopsmussels Most sessile, benthicMost are filter feedersNo head or radulaBurrow

Sand, wood, rocks A few can use muscular foot that extends from shell for

movement

Scallops clap valves together to move

Class Bivalvia

Shell secreted by mantle

Oldest, raised part of shell called umbo

Have an incurrent & excurrent siphon that circulate water over the gills to remove food & oxygen

Have heart & open circulatory system

Class Cephalopoda

Octopus, squid, cuttlefish, & chambered nautilus Move by using mantle cavity as jet propulsion

Sucks water into mantle cavity, pushes water out of muscular siphon that can change size (speed) and direction.  

Most intelligent mollusk Well developed head –centralized brainLarge eyes, visual predatorsLack outer shell, very flexibleActive, free swimming predatorsFoot divided into tentacles with suckers   

Class Cephalopoda

Chromatophores: can change color, used for camoflauge and social signaling. 1st group with social signaling-reguires

more complex brain to interpret signals

Use their radula & beak to feed Closed circulatory system Highly developed nervous system

with vertebrate-like eyes Sexual reproduction

Separate sexes with internal fertilization

Class Cephalopoda

SQUID Largest invertebrate is the Giant Squid Large, complex brain 8 tentacles 2 arms- longer pair to catch prey Use jet propulsion Chromatophores Have internal shell called pen

Class Cephalopoda

Can squirt an inky substance into water to temporarily blind predators

Class Cephalopoda

OCTOPUS Eight tentacles Similar to squid Sit & wait predators = ambush Female dies after tending to eggs. Beak like jaws, radula

Importance of Mollusks

Filter water, healthy watersKeep algae growth doneFood for top predators and

economically important species.

Used  by humans for food Pearls from oysters Shells used for jewelry