Invertebrates lab exam 2

5 characteristics of the generalized mollusc

1. A poorly developed head

2. The ventral body surface is flattened into a muscular foot

3. A visceral mass contains many of the internal organs

4. The dorsal body surface is covered by a shell

5. A mantle (pallium) secretes the shell

ctenidia

• comb-like gills found in the mantle cavity of most molluscs

radula

• a ribbon made of chitin and protein and covered in sharp chitinous teeth

• common characteristic in Mollusca

features of the buccal cavity in most molluscs

a toothed radula, salivary glands, and digestive glands

vascular system in molluscs

includes blood (which contains a respiratory pigment), a heart, blood vessels, and often a hemocoel

hemocoel

• a “blood cavity” in which sits the internal organs

• Blood is pumped into the hemocoel and bathes the organs so that gas exchange and other processes can occur

• can also act as an efficient hydrostatic skeleton

do molluscs have a coelom

• reduced to a small space surrounding the heart and gonads and has no role in locomotion

3 classes in phylum Mollusca

1. gastropoda

2. bivalvia

3. cephalopoda

3 informal groups in class gastropoda

1. prosobranchs

2. opisthobranchs

3. pulmonates

example of a genus in group prosobranch

Busycon sp. (Atlantic whelk)

example of a genus in group opisthobranch

Dendronotus sp. (sea slug)

2 examples of genus in pulmonates

• Helix pomata (land snail)

• Argiolimax sp. (land slug)

3 examples of genus in class Bivalvia

• Anodonta sp. (freshwater clam)

• Mytilus edulis (sea mussel)

• Teredo navalis (North Atlantic shipworm)

4 examples of genus in class Cephalopoda

• Nautilus sp.

• Octopus sp.

• Sepia sp. (cuttlefish)

• Loligo sp. (squid)

general traits of class Gastropoda

• habitat: marine, freshwater, and terrestrial

• feeding strategies: herbivory, carnivory, suspension-feeding,
  deposit-feeding, and ectoparasitism

• some display torsion and spiraling

torsion

• a 90-180o counterclockwise twisting of most of the gastropod body (visceral mass, mantle, and mantle cavity)

• occurs during larval development

• results in spiraling

spiraling

• due to torsion

• spiraling of the visceral mass, mantle, and overlying shell

consequence of torsion and spiraling

increasing asymmetry of the organs of the visceral mass with a reduction and loss of the organs on one side of the body (usually the right side)

traits of group Prosobranch

• most primitive gastropod group

• mostly aquatic but some freshwater and terrestrial

• exhibit torsion, resulting in the mantle cavity, gills, and anus being located anteriorly

• only a single pair of tentacles on the head

• operculum attached to the foot

operculum

• used to block the opening of the shell in prosobranchs

• a hard disc of protein occasionally strengthened with calcium carbonate

traits of Busycon sp.

• aka Atlantic whelk

• displays torsion resulting in spiraling of the visceral mass

• basic features: head, foot, visceral mass, and mantle

• single pair of tentacles on the head with a small eye at the base of each one

• operculum

• proboscis

proboscis

• long retractable snout with a mouth at the end

• used to capture and consume food

columella

• central axis of a prosobranch shell

• As the animal grows, its body coils around the columella

columellar muscle

• attached shelled mollusc to the inside of the shell

how do prosobranchs carry their shells

• Typically, the shell is carried such that it leans to the left

• As a result, the shell axis is oblique to the long axis of the body, which balances the animal’s centre of mass over the foot

dextral shells

• shells that are coiled clockwise (to the right)

• opens on the right

sinistral shells

• shells that are coiled counter clockwise (to the left)

• opens on the left

traits of group opisthobranchs

• detorsion or limited torsion during development

• reduction, internalization, or loss of the shell

• reduction or loss of the operculum

• reduction or loss of the mantle cavity

• reduction or loss of the gills

• head commonly has two pairs of tentacles (second pair called rhinophores)

• visceral mass is often incorporated into the head-foot complex

• bilateral symmetry

rhinophores

• second pair of tentacles in opisthobranchs

• chemosensory function

detorsion

• unwinding of the body after torsion occurs

• common in opisthobranchs

traits of dendronotus

• aka sea slug or nudibranchs

• respiratory structures called cerata

• lack a shell (have unique defensive mechanisms as a consequence)

• visceral mass incorporated into head-foot complex

• lack gills

what does nudibranch mean

naked gills

cerata

• respiratory structures in sea slugs (instead of gills)

• usually contain extensions of the digestive system

• dorsal projections

example of a defense mechanism in dendronotus

• presence of nematocysts in the cerata of some species

• unfired defensive organelles are remnants from cnidarian prey and can
  be used to defend against would be predators

traits of Pulmonates group

• detorsion

• reduction or loss of shell

• 2 pairs of tentacles on the head

• lack gills and instead have a lung that is a vascularized mantle cavity

Pulmonates habitat

• mostly freshwater or terrestrial

• if marine only live in intertidal zone or estuaries

how does gasexchange work in Pulmonates

• Water or air can be drawn into the mantle cavity by depressing the floor of the cavity, thereby increasing its volume and creating negative pressure

• That same water or air can then be expelled through a small opening called the pneumostome by raising the floor of the cavity to decrease the volume and increase the pressure

pneumostome

small opening in the mantle cavity of Pulmonates that allows the air or water to be expelled

traits of Argiolimax

• common land slug

• 2 pairs of tentacles

• eyes are located at the end of one pair of tentacles

• highly reduced internal shell

traits of Helix pomata

• edible land snail (aka escargot)

• very thin shell

• has a radula for feeding

why does Helix pomata have a thin shell

• shell can’t be too heavy or locomotion would be very difficult

• tradeoff- still have shell for protection but is thin and easily damages because snail needs to be able to move

why do aquatic gastropods have thicker shells

Aquatic gastropods can have thicker and heavier shells since the buoyant effect of the water compensates for the weight of the shell

radula

• a feeding structure consisting of a ribbon made of chitin and proteins covered in sharp chitinous teeth

• scrape food off a substrate by extending the anterior end out of the mouth and running it along the surface of the substrate

• if the anterior end of the radula wears down, new pieces of the ribbon and teeth are constantly being produced at the posterior end to replenish the radular surface

Class bivalvia habitat and lifestyle

• sessile, sedentary, or burrowing forms

• majority of species are marine, but a small percentage are found in freshwater

• suspension feeder

class Bivalvia physical traits

• shell composed of 2 valves

• the foot and visceral mass (which extends into the foot) are laterally compressed

• head is very reduced and represented by 2 labial palps on either side of the mother

• absence of radula

• hinge of 2 valves is the dorsal part of the organism

traits of an Anodonta shell (clam)

• valves attached at hinge by a ligament that opens shell when adductor muscles relax

• scars on inner surface are where adductor muscles were attached

• pallial line runs between scars and is parallel to the free edge of shell

• bulge by the hinge called the umbo

• Growth lines run parallel to the shell’s outer margin

adductor muscles

• powerful muscles that attach to to each valve at the scars

• when they contract the clam shell closes

• when they are relaxed the shell opens

pallial lines

• faint line that runs between the scars

• parallel to the free edge of the shell

• where the mantle attaches to the shell

umbo

• bulge on the hinge of the shell

• comprised of the earliest shell material deposited by the animal

physical traits of anodonta

• the foot and visceral mass are laterally compressed

• foot is shaped like a “hatchet” which is great for digging

• shell is heavy and laterally compressed and can be used as a wedge while digging

• gills are primary respiratory organs and used for filter-feeding

• gill cilia create a current of water through the mantle cavity and capture
  food particles

glochidium larvae

• clam larvae

• microscopic, non-swimming, shelled larvae

• develop for weeks as an external parasite on fish before dropping off and settling to the bottom to begin its life as a benthic individual

clam life cycle (glochidium larvae)

• product of sexual reproduction

• Sperm are released into the water by males and drift into the gills of females, fertilizing the eggs held in the area

• fertilized eggs develop into glochidium larvae in the females gills and then are released

• must latch to a passing fish or vertebrate host to survive

• many larvae are produced since many do not find a host

traits of Mytilus edulis

• Blue sea mussel

• live attached to hard surfaces near intertidal zones

• have byssal threads to stay attached to surface during strong waves

byssal threads

• specialized anchoring structures that ensure mussels are able to stay attached to the substrate in turbulent conditions

• secreted by a gland at the base of the foot

• once they contact seawater, they solidify

traits of Teredo navalis

• north atlantic shipworm

• reduced shell which is specially designed for cutting through wood

• often damage wooden structures found in marine environments

• filter seawater through their gills to capture food particles

• ingest small bits of wood that are broken free by the action of their shell

• have symbiotic bacteria in their guts which help them extract nutrients from the wood

physical traits of class cephalopoda

• body has an elongated dorsoventral axis, which has become the functional anterior-posterior axis

• head is well developed and associated with the foot which makes up the arms and tentacles (both have suckers)

• internalized and reduced shell (usually)

• closed circulatory system

difference between arms and tentacles

arms have suckers along most of their length whereas tentacles only have suckers at the end

closed circulatory system

• in which blood flows through a system of arteries, capillaries, and
  veins, before returning to the heart

• adequately meets the oxygen demands of the body

what adaptations do cephalopods have to allow them to swim fast

• internal and reduced shell

• closed circulatory system

traits of Nautilus

• only living cephalopod with an external shell

• shell is divided internally into compartments by septa

• the living organism lives in the largest outermost chamber

• siphuncle spirals through all chambers of the shell

• lack chromatophores because have shell for protection

• 80-90 arms

siphuncle

• calcified tube that spirals through all chambers of a Nautilus’ shell

• transfers liquid from one chamber to another

• Gases can also diffuse into or out of chambers using the liquid in the siphuncle

• allows the animal to control its buoyancy in the water column

chromatophores

• allow non-shelled cephalopods to change color for camouflage or mating

traits of octopus

• lost shell completely

• have many chromatophores in their skin and use the to blend into their surroundings

• have 8 arms (not tentacles because suckers extend the entire length)

traits of sepia

• aka cuttlefish

• adapted for swimming by being broad, flat, and elongated in the dorsoventral axis = streamlined = glides through water

• 8 arms and 2 longer tentacles

• tentacles can be extended to latch onto a substrate or to capture prey and reel it in to the area of the arms and mouth

• internal shell with compartments fluid and gases that can be adjusted to control buoyancy

traits of loligo

• aka squid

• 8-10 arms and 2 longer tentacles

• mouth with hard pointed jaws

• thick mantle = more muscle to help with fast swimming

• Some of the muscular tissue of the mantle is involved in circulating water to the gills for oxygenation

• has a funnel

• has a closed circulatory system

• has accessory hearts called branchial hearts

• internal shell called a pen

cephalopod eye traits

• highly developed because fast swimmers and predators

• move the entire lens towards or away from the retina to focus the light

• similar to human eyes = convergent evolution

how does Loligo swim

• use jet propulsion-like movement

• contraction of the muscles within the mantle changes the volume of the mantle cavity and draws water into the cavity

• The collar of the mantle then constricts to form a tight seal around
  the head

• The trapped water is then forcefully expelled through a structure called the funnel and this action propels the organism

• The funnel is flexible and can be oriented to help “steer” the organism

why is oxygenation important for Loligo

organism is very active and needs lots of oxygen to swim fast

Loligo circulatory system

• closed circulatory system creates a higher blood pressure (much like our own system)

• oxygenation of tissues and transport of nutrients are very efficient
  processes

• allows cephalopods to grow to large sizes and out-compete their prey items

branchial hearts

• accessory hearts in Loligo

• pump blood specifically to the gills in order to force extra blood through the respiratory structures and pick up extra oxygen needed for their active lifestyles

pen

• thin, internal, stiff, proteinaceous “shell” in Loligo species

• reduced weight and internal positioning still gives support to the body but it doesn’t hinder the speed of movement

• no role in buoyancy regulation
  

cephalopod hearing

• do not respond to sounds unless very low frequency

• adaptive change in the physiology of cephalopods in response to the hunting methods of toothed whales and dolphins which have hunted them for millions of years

• these predators stun their prey with high frequency sounds and so by being “deaf” to these attacks, cephalopods have a better chance of evading capture