Phylum MolluscaClass Aplacophora - Small + wormlike, primitive (no shell) Class Monoplacophora - Deep sea, cap-like shell; segmented? Class Polyplacophora - Chitons

Class Gastropoda - Snails + slugs

Class Bivalvia - Clams, mussels, oysters

Class Cephalopoda - Octopus, squid, cuttlefish, nautilus

Class Scaphopoda - Tusk shells

~20,000 species

Shell of 2 valves, left + right; hinged by ligament on dorsal side- held together by adductor muscles

Byssal threads (protein) anchor some to hard substrata

Reduced head, no radula; most are filter-feeders

No eyes on head, but can have numerous eyes on body

1 large pair of ctenidia used in filter feeding + gas exchange

Large mantle cavity, often with mantle edges fused into large siphons for water intake

Class Bivalvia

~20,000 speciesClass Bivalvia – clams, mussels

Ctenidia = gills, used also in filter feeding

Shell

foot

Shell with 2 valves, held together by powerful adductor muscles (the meat of a scallop)

Labial palp, scrapes food off gills and into mouth

Class Bivalvia – clams, mussels

Shell

Anterior adductor muscle

foot

Shell with 2 valves, held together by powerful adductor muscles (the meat of a scallop)

Foot used for digging into bottom

Posterior adductor muscle

Muscle scars can be identified inside a bivalve shell

serrations

pedal retractor

hinge ligament

umbo

pallial line

posterioradductor muscle

anterioradductor muscle

Bivalve shell: Muscle scars

Muscles & ligaments control the opening and closing of the bivalve shell

When muscles relax, inner ligament pushes out shell opens

When muscles contract, inner ligament is compressed shell closes tightly

a relaxed clam opens its shell; staying shut takes energy

Self-test : know the major anatomical features of a bivalve

Bivalves filter-feed with their gills

Use their ctenidia (gills) for both filter feeding & respiration

- clams burrow into mud/sand; use siphon to draw in water, pass it over their gills for both oxygen and food

Cilia (tiny hairs) beat to generate water currents

(like sponge choanocytes)

Trap tiny particles, which are then carried to the mouth

to mouth

Food particles are swept into food groove at base of W - scraped off, sorted by labial palps - passed to mouth - unsuitable particles rejected as pseudofeces

food groove

Byssus

- foot is held firmly against a hard surface (rock, other shells)- gland secretes a liquid protein that drips down foot groove- protein hardens into tough thread, sticks out of gland- foot releases from surface, then re-planted and repeat process

Foot is a thin, grooved appendage used to pour the fast-hardening liquid prottein that forms byssal threads

mantle

posterioradductor muscle

foot

ctenidium

palp

Byssal glandByssal threads

Anatomy of the Mussel Mytilus

anterior adductor muscle is greatly reduced

ctenidia are thin flaps that fill most of the shell

Anatomy of the Mussel Mytilus

Mussels: Dominant Spatial Competitors

Mussels cover rocks in the intertidal zone out-compete other organisms for space, unless their #’s are limited by predators

use fast-hardening protein to form byssal threads that glue them to rock surface

Space Invaders

The ability of bivalves to occupy space, reproduce in huge numbers, and efficiently filter feed has made them particularly disruptive invasive species in many ecosystems

- devastatingly harmful, both ecologically and economically

Dreissena (zebra mussel)

– spread from Europe to Great Lakes, down Mississippi to 20 states

– economic loss of >$5 billion so far

Space Invaders

The ability of bivalves to occupy space, reproduce in huge numbers, and efficiently filter feed has made them particularly disruptive invasive species in many ecosystems

- devastatingly harmful, both ecologically and economically

Dreissena – spread from Europe to Great Lakes to 20 states (zebra mussel) – economic cost: >$5 billion to date

Potamocorbula – alien clams filter San Fran Bay so thoroughly, eliminated the spring phytoplankton bloom

Musculista – Asian Date mussel, advancing across the globe

The giant clam genus Tridacna includes the largest bivalves

- may be 4 feet long, >400 pounds, 100 years old

Inhabit nutrient-poor tropics: not much to filter feed on

Mantle tissue is filled with zooxanthellae symbionts, same as hard corals

- release fixed carbon to fuel clam growth

- now endangered from over-fishing

Unionids: Endangered freshwater musselsFreshwater mussels evolved “vampire larvae” called glochidia that clamp onto fish gills and drain nutrients from their host

- larvae don’t get washed downstream, have plentiful food source

Females show amazing adaptations to lure their host fish close enough to spray larvae into the fish’s gills

- most Unionids have one fish species that acts as a host

- many Unionids are now endangered as a result of human activity that disrupts freshwater ecosystems

glochidia

Freshwater mussels (Unionids)

femalemussel

edge of mussel’s mantle

Freshwater mussels mimic small fish, insects with parts of their body to lure larger, predatory fish spray vampire-larvae into big fish’s gills, where the larvae drink its blood!

actual prey fish

Glochidia larvae (220 m)

...Glochidia are released into the fish’s face, where they clamp on to the thin gill tissue

Other species produce clumps of eggs called ovisacs that mimic insect larvae

- these mimic blackfly larvae clinging to rocks

When a fish bites the ovisac, it ruptures, releasing glochidia into the fish’s gills

Phylum MolluscaClass Aplacophora - Small + wormlike, primitive (no shell) Class Monoplacophora - Deep sea, cap-like shell; segmented? Class Polyplacophora - Chitons

Class Gastropoda - Snails + slugs

Class Bivalvia - Clams, mussels, oysters

Class Cephalopoda - Octopus, squid, cuttlefish, nautilus

Class Scaphopoda - Tusk shells

SubClass Nautiloidea (chambered shell)

Class Cephalopoda

Subclass Coleoidea

Order Octopoda - octopuses

Order Sepioida - cuttlefish

Order Teuthoida - squids

complete loss of shell

shell reduced to internal remnant

Most intelligent invertebrates, complex eyes

- Only molluscs with closed circulatory system: hunt by zooming backwards by high-speed jet propulsion

- flex mantle muscles, forcing water out of siphon

- Defense without a shell: inking, color + texture change

- Foot divided into prehensile tentacles with flexible suckers

Nautilus, squid, octopus

Class Cephalopoda ~900 species

nautilus squid octopus

(external shell) (thin, internal shell) (no shell)

Nautilus lives at >600 meters deep; comes to surface at night to hunt, catching prey with its tentacles

- pumps gas into sealed chambers through tube called the siphuncle, to adjust buoyancy (floaty-ness)

siphuncle

Chambered Nautilus

- elongated body with lateral (side) fins- 8 short arms + 2 long tentacles

Order Teuthoida (squids)

Order Teuthoida (squids)

fin

ventralarms

contractilearms

siphonsuckers

club oftentacle

Order Teuthoida (squids)

Fast-moving mid-water predators

shoot out 2 extra-long tentacles to snag fish, using their suckers

internalshell

Squid

giant squid = world’s biggest invertebrate

Giant squid,Architeuthis

Euprymna scolopes

Bioluminescence results from light- producing bacterial symbionts

- Vibrio bacteria live in a shuttered organ the squid can selectively open to emit desired amount of light

- bacteria glow whenever they are at a threshold density in the light organ

Glow-in-the-dark squid

Euprymna scolopes

Bioluminescence results from light- producing bacterial symbionts

Mid-water squid use light for counter- shading to hide from predators below

nocturnal squid cast a shadow when there is moonlight, which predators see and attack from beneath

Glow-in-the-dark squid

by opening shutters on light organ, squid releases same amount of light from ventral side as is hitting its dorsal surface

no shadow visible to predators beneath them; essentially, become invisible

Euprymna scolopes

Glow-in-the-dark squidQuorum sensing is how bacteria tell when there’s enough of them present to start glowing (or doing other things)

- each cell releases a chemical signal

- when enough signal builds up, all cells turn on genes required for bioluminescence

- studies on this process led to breakthrough understanding of how bacteria cooperate during human infections: they wait until quorum sensing indicates sufficient #’s to turn on pathogenicity genes and mount an attack

- led to a whole new line of research, looking for antibiotics that disrupts bacterial communication

Loligo, the reef squid

Order Sepioda (cuttlefish)

Eye

Tentacle

ArmsFin

most precise ability to mimic background color of any animal

chromatophores - colored pigment sacs expand or contract to change color

iridocytes - light reflectors in skin

Order Sepioda (cuttlefish)

- body short & round- no fins- no internal shell- 8 similar arms- mostly benthic

advanced brain with many distinct lobes

ability to learn, even by observing other octopuses perform a task

~200 spp.Order Octopoda

- 8 arms- no shell- best vision- smartest invertebrate

~200 spp.Octopus

Cross-section of arm

ctenidium siphon

buccalmass

Octopus’ Compound Eye

pigment cells

sensory cells

Cornea

Epidermis

Iris

Retina

most advanced compound eye of any invertebrate

image-forming, much like our camera eyes