Week 6 Flashcards
Phylum Mollusca characteristics
"soft" lophotrochozoa protostomes coelomates 90,000 species marine, freshwater, and terrestrial herbivorous grazers, predatory carnivores, filter feeders, parasites
first group of larger animals to transition to land
Phylum Mollusca
what is possible the second largest group after anthropods
Mollusca
what do molluscs have on pseudocoelomates
true coelom advanced locomotion circulatory system (open or closed) with heart and vessels respiratory organs (lungs or gills) complex sensory structures (highly developed eyes in cephalopods)
what does the coelom surround in molluscs
the heart
are molluscs eyes analogous or homologous with human eyes
they are analogous
mollusc definition
coelomate protostomes possessing a shell-secreting mantle, also possessing a radula, digestive gland, metanephridia, gills, and an open or closed circulatory system with a heart
metanephridia
simple kidney, similar to protonephridia,
what does the metanephridia help with
excretion
where are protonephridia generally found in
things without a coelom or vascular system,
where are metanephridia found in
things with a coelom and vascular system
Molluscan diversity
Class Caudofoveata & Class Solenogastres- small group of worm like animals, mainly deep sea
Class Polyplacophora & Class Monoplacophora- “many plates” (chitons) or “one plate”
Class Scaphopoda- “shovel foot”, tusk/tooth shells
Class Gastropoda- snails and slugs, largest mollusc group
Class Bivalvia- clams, mussels, mostly filter feeders, some freshwater forms
Class Cephalopoda- squids, octopuses
Class Caudofoveata & Class Solenogastres
lack shells but have a calcareous scales or spicules in skin
Class Polyplacophora & Class Monoplacophora
chitons with 7-8 plates, monoplacophora have one cap-like shell
rocky intertidal surfaces
don’t move much, chitons curl up into ball when dislodged
serial repetition of soft parts (gills) seen in monoplacophorans
Class Scaphopoda
tube shells open at both ends, burrow larger head into sand, leave smaller end open to water
how much does class Gastropoda make up of all living mollucs
80%
some molluscs that are important food sources
escargot, abalone
Class Cephalopoda
foot modified into arms
active predators
well developed nervous and sense organs, closed circulatory system
Phylum Mollusca overall complexity
head-foot
visceral mass
mantle
shell
head-foot
most have a distinct head with a mouth (containing radula) and sensory organs
foot is chief locomotor organ, modified in different ways in different groups
visceral mass
contains organs, digestion, circulation (heart connects to gills), excretion (metanephridia), reproduction
mantle
mantle cavity is space between protective mantle (which secretes shell) and the body, houses gills or lungs
what is essentially molluscs body
head-foot and visceral mass
can be extended to include mantle
phylum mollusca
complexity and feed
uses teeth on radula to rasp off bits of food from hard surfaces
supported by odontophore
odontophore
cartilaginous rod
supports radula
attachment for muscles
radula
protruding, rasping, tongue-like organ
radula teeth made of chitin, constantly replaced (produced posteriorly, used at apex, lost anteriorly)
how is feeding modified in some molluscs
bivalves- filter feeders
cephalopods- beak and jaws for seizing prey
phylum mollusca
visceral mass- digestive system
digestive system more complex and generally highly specialized to correspond with feeding habits
radula brings food into mouth, digestive gland secretes enzymes for digestion in stomach
phylum mollusca
visceral mass- circulatory system
no distinction between blood and interstitial fluid- hemolymph
open system more common in slow moving animals, more active animals (like cephalopods) generally need a closed system because it is more efficient
heart pumps blood out to body, muscles move blood back to gills.
pericardium
fluid-filled sac, encloses the coelom (and the heart)
how does circulation occur
heart pumps blood to body, muscles move blood back to gills
what does hemocyanin do
acts as O2 carrier, has two copper atoms that reversibly bind a single oxygen molecule, binds O2 at gills where it is abundant and releases it in tissues where there is a deficit
what color blood does molluscs have
blue
phylum molluscs
visceral mass- excretory system
metanephridia are similar to protonephridia but inside of the tube is ciliated to move fluid
organisms with vascular system and coelom have filtration and excretion happening in two different sites
phylum mollucs
response to stimuli and movement
muscular foot
muscular foot
usually ventral
attachment or locomotion
sometime secrete mucous for adhesion or to help glide on cilia
modifications to muscular foot
attachment disc of limpets
hatchet foot of bivalves
siphon and arms of cephalopods
mantle
sheath of tissue on each side of body
forms lobes at outer edge
what does the mantle secrete
shell (if there is one)
what does the mantle cavity house
gills/lungs
what does the exposed mantle surface function in
gaseous exchange
what systems empty into mantle cavity and out to environment
excretory and reproductive
what does the mantle in aquatic forms usually contain
chemoreceptors
what does cilia in mantle cavity do
form water currents to carry waste and reproductive products out and bring in oxygen and, in filter feeding forms, food
layers of shell
periostracum
prismatic layer
nacre
periostracum
organic layer or “skin” made of protein, protects underlying layers
prismatic layer
protein and calcium carbonate, secreted at mantle edge
nacre
mother of pearl, in thin translucent sheets, secreted by epithelium so older parts of shell have thicker layers
how is a pearl formed
when something is lodged between mantle and nacre, mantle secretes layers of nacre around it as a defensive mechanism
phylum mollusca reproduction
usually reproduce sexually ( some parthenogentic- development without fertilization)
most are dioecious
some simultaneous hermaphrodites- gonads= ovotestis
shed eggs/sperm into mantle cavity and then out into environment for fertilization
free swimming trochophore stage is characteristic in aquatic species, often followed by a veliger stage
veliger stage
has beginnings of foot, shell, and mantle
is veliger stage seen in cephalopods
no, they hatch miniature adults
class gastropoda critters
snails, slugs, conchs, nudibranchs
class bivalvia critters
clams, mussels, oysters, scallops
class cephalopoda critters
squids, octopuses, nautiluses, cuttlefishes
gastropoda
largest and most diverse mollusc group
body elongated dorso-ventrally and then coiled inside shell; also turn whole shell around so that anus is over head (torsion)
how does gastropoda move
usually through waves of muscular contraction in foot, may be mediated by cilia and/or mucus; tend to be pretty sluggish
what do pulmonate land gastropods have
mantle cavity developed into simple lung
gastropod quirks
torsion
coiling
strategies to avoid fouling
where is veliger larva mouth and anus
mouth anterior, anus posterior
torsion
start with straight mouth to anus tract in veliger, then muscles start to contract and shell (and viscera inside) are pulled 0 degrees
mantle cavity starts to form near anus, and continue rotating (shell mostly stays put) until anus and mantle cavity are in front
occurs during development
what does putting butt over head do
increases possibility of wastes washing back over gills and mouth (fouling)
why does torsion happen
moves respiratory organ to anterior, might increase efficiency
mantle cavity has chemosensitive organs, so makes sense to move it in front to better sample water/air in the direction it is headed
may make it easier to withdraw head inside shell
did coiling or torsion evolve first
coiling
coiling
ancestral planospiral shell is not very compact and has high center of gravity
evolved into more compact form with successive whorls lying outside preceding one
this is unbalanced so it shifted over, excess weight on right side led to loss of kidney and gill on right side
what made the adaptations to avoid fouling happen
loss of gill
adaptations to avoid fouling in gastropods
water flows one way into left side and out of right side
circulation through mantle cavity has been modified to move gill to anus and then out of mantle cavity
how do cone snails eat
with modified hollow barbed radula tooth to stab and inject venom into prey before engulfing it
what does conotoxin do
immobilize prey and then harpoon is retracted and prey is eaten
can conotoxin be dangerous to humans
yes
how is conotoxin useful in medical research
venom in precise and fast acting, allowing quick results with few side effects
also contains pain reducing compound
snail love darts
dart success not related to copulation success or size of ensuing sperm donation
BUT dart success increases amount of sperm stored by recipient
AND dart success increases relative paternity when competing with an unsuccessful dart shooter
where does interanal fertilization required to occur in gastropods
to live on land
requires more complicated reproductive system
class bivalvia
body generally reflects adaptations for sedentary suspension feeding
two shells with a hinge, laterally compressed body
mantle cavity and gills greatly enlarged- gills function in gas exchange and in food acquisition (pull water through for feeding)
foot modified to be burrowing organ and also sometimes drives water across gills by pumping
generally lack head and radula (tend to lack cephalization in general)
bivalve feeding
water moves through incurrent siphon and then along external aspect of gills, then through gills to interior aspect and out through excurrent siphon
food particles get stuck to mucus on surface of gills and then are moved via cilia towards mouth, where labial palps use mucus to form a bolus (ball of food and mucus) that is ingested
bivalve locomotion
burrowing
burrowing
extend foot
expand foot to “anchor” via lateral pressure
contract foot to move body in direction of foot, siphons extend in order to maintain fluid flow through mantle cavity, usually accompanied by opening and closing of shell to loosen sand
human impact on bivalves
toxins in water poison them then they poison us
invasive species such as zebra mussels are in issue in many water ways
problems caused by zebra mussels
damage and clog water treatment plants
out compete native species
largest of all invertebrate animals
Architeuthis, giant squid can get up to 40 feet long
class cephalopoda
dorso-ventrally elongated
head becomes merged with foot
foot modified to form arms, tentacles, and funnel/siphon used for jet propulsion by taking water into mantle cavity and forcefully expelling
often a reduction or loss of shell
adaptations for predation
highly intelligent well developed eyes strong swimmers closed circulatory system arms, tentacles, and beak for capturing prey
eye evolution in molluscs
simple eye spots, allow for light detection but that’s it
pigmented cup, allows for light detection as well as determining direction
“pinhole” eye allows for better directional sensitivity and limited image formation, but low-light
primitive lens, allow for slightly better focus and brighter, but no ciliary muscle so can’t alter point of focus
lensed eye allows for focused images and can alter lens or move forward/backward to alter point of focus
do cephalopods have blind spots
no but have less blood flow to retina
chromatophores
pigment cells in the skin
can expand and contract to change color
what allows cephalopods to change texture
papillae
cephalopod sex
dioecious
internal fertilization
males use a hectocotylus, or hectocotylized arm
hectocotylized arm
modified arm with pocked for transferring spermatophores
can a hectocotylus be detachable
may be detachable
useful to deposit sperm and leave before being eaten
