Phylum Mollusca Flashcards
the shell of molluscs is made of:
calcium carbonate
defining characteristics of molluscs (3)
- dorsal epithelium forms mantle
- radula (except bivalves)
- ventral body wall muscles develop into foot
chitons (class)
Class Polyplacophora
chitons have how many osphradia?
two
defining characteristics of chitons (5)
- minimal cephalization
- dorso-ventral flattening
- 8 shell plates
- thickened mantle - ‘girdle’
- radula with magnetite-capped teeth
significance of the 8 shell plates
bodies can conform to uneven topography
how does the mantle of chitons assist with substrate adhesion?
press with the periphery of mantle and raise interior of mantle cavity to create negative pressure for suction
what is the function of magnetite caps on teeth
hardening of radular teeth
where are the two osphradia of chitons located
either side of the anus
differences between coelomic compartments in annelids vs. molluscs
molluscan compartments are much smaller
dorsal blood vessel is more muscular- forms ‘heart’
ultrafiltration into the perciardium
connection between gonads and pericardium lost in molluscs
radula of molluscs are inside of the:
buccal mass
teeth of radula are secreted by the:
radular sac
____ are the only molluscs lacking radula
bivalves
chiton reproduction
dioecious
broadcast spawn gametes
external fertilization
larva of chitons is similar to
trochophore larva (ciliated and non-feeding)
chitons have which type of ctenidia
bipectinate
blood flow is ____to the direction of water flow in chitons
opposite - countercurrent exchange
monoplachophora is sister to all other____
conchiferans
monoplachophorans have __ pairs of metanephridia and __ pairs of gonads
2; 2
which is the largest class of molluscs?
gastropoda
2 major defining characteristics of gastropods
- torsion
2. operculum
2 major body regions of gastropods
cephalopodium and visceropallium
the shell of gastropods evolved as:
a protective retreat for the head and foot
what is the columella in gastropods
the central column of calcium carbonate that the shell coils around
the ancestor of all gastropods was likely ___-like
monoplacophoran
the contraction of which muscles draws the head and foot into the gastropod shell
columellar muscles - extend from the foot to the central axis
function of the operculum in gastropods
drawn in last (following the head and foot) and seals the operculum of the shell
according to the torsion hypothesis, what happens between the monoplacophoran state and intermediate state?
reduction of:
- shell aperture
- # of shell muscles
- # of ctenidia
- posterior mantle cavity
according to the torsion hypothesis, what happens between the intermediate state and gastropod state?
180 degree rotation of the visceropallium relative to the cephalopodium
evidence for torsion (2)
- anatomy of living gastropods - crossover of visceropallial nerve cords
- development of basal gastropods - rotation during development
adaptive value of torsion in larval stages
survival adaptation - carried into the adult stage
adaptive value of torsion in adult stages
ctenidia and osphradia become located at the front, in the direction of locomotion
what is the fouling problem in gastropods
the anus discharges over the head - inefficient turbulence and circulation of water in the mantle cavity might have fecal material
solutions to the fouling problem (2)
- shell perforations : one way water flow lessens contamination (vetigastropoda)
- shift of the anus to the right side (caenogastropoda)
all vetigastropods have shell perforations and __ ctenidia
two
caenogastropods lose the ____ ctenidia as the anus shifted to the right side
right
what is the primitive feeding strategy of gastropods
herbivorous grazing using radula
feeding strategies of caenogastropods (2)
- herbivorous grazers
2. predators - use proboscis
what makes predatory gastropods unique?
- expanded body wall around the mouth
- body wall opens into proboscis sac
- elongation of anterior esophagus
what makes shell drills unique?
- accessory boring organ at the tip of the proboscis
- likely secrete toxins
- mucus and sand used to produce egg case
elaboration of mid-esophageal gland in moon snail
elaborated into venom gland that excretes conotoxins
what is unique about the proboscis of moon snails?
no radular ribbon of teeth - hollow harpoon at the end of the proboscis instead
what are conotoxins?
small peptides that target neural antigens
defense strategies of marine heterobranchs (4)
- chemical defense - toxic secondary metabolites taken from prey or secreted by themselves
- escape/defensive behaviour - flexions takes them to prevailing current to carry them
- sequestration of cnidocytes - store nematocysts from cnidarians in cnidosacs
- autotomy - cell cutting of cerata along autotomy plane
adaptations of terrestrial heterobranchs (3)
- mantle cavity forms internalized ‘lung’ with pneumostome to exterior
- conversion of ammonia to uric acid to preserve water
- aestivation - metabolic slow-down, tolerate dessication and rapidly rehydrate
reproduction strategy in vetigastropods
broadcast spawning - external fertilization
reproduction strategy in caenogastropods and heterobranchs
internal fertilization and encapsulated eggs
gastropod larval type
veliger larvae
major characteristics of class bivalvia (5)
- laterally compressed
- 2 lateral shell valves hinged dorsally
- spacious lateral mantle cavities - each with ctenidium
- minimal cephalization
- no radula
what is the foot used for in bivalves
burrowing
adductor muscles in bivalves are used to:
close the shell
how do bivalves burrow
contraction of circular muscles projects the foot into the substrate, the foot then expands to form terminal anchor
what is the periostracum of bivalves?
layer of protein secreted by between middle and outer lobes - covers the calcium carbonate shell
where do the pallial muscles of bivalves insert?
run from the inner lobe to the point where the mantle touches the shell
what are the pallial muscles used for?
pull the periphery of the mantle fold into the shell so it can be closed tightly without tissue caught inside
3 lobes of bivalves and their function
- inner lobe - muscular
- middle lobe - sensory
- outer lobe - secretes periostracum
what is the function of hinge teeth
interlock to prevent shell valves from laterally slipping
how do protobranchs feed
deposit feeding using palp tentacles
the ctenidia of protobranchs are used for:
gas exchange only
most bivalves have ______ ctenidia
lamellibranch
3 types of cilia on demibranch of lamellibranch ctenidia
- lateral cilia - create water current/draw water in
- laterofrontal cilia - intercept flow of particles
- frontal cilia - carry particles to frontal apex ‘elbow’ of gill filaments
septibranchs feeding strategy
predators
- use suction via inhalant siphon to suck prey into mantle cavity
- highly modified gill with perforations elevates and increases volume of mantle cavity to create negative pressure
which bivalve has byssal threads and what are they used for
mussels - byssal threads are secreted by byssal glands for attachment to rocky substrates
how does attachment work in mussels
byssal gland secretes liquid that runs down a groove in the foot and creates puddle on the substrate
- the foot is then removed and byssal strands remain to keep the mussel attached
what allows shipworms to damage wood
ctenidia are populated with enzymes that break down cellulose
defining characteristics of Class Cephalopoda (4)
- shell divided by septa - chambers connected by siphuncle
- closed circulatory system
- foot modified to form flexible arms and siphon
- ganglia fused to form large brain enclosed in cartilaginous cranium
molluscan characteristics found in cephalopods (3)
- radula
- molluscan - style ctenidia (but not ciliated)
- shell secreting mantle (shell often reduced or lost)
distinctive characteristics of Cephalopods (different from other molluscans (2))
- septate shell
2. highly modified foot
what is the difference between a funnel and a siphon
funnel is derived from foot tissue
which cephalopods show the most primitive characteristics
nautilus
characteristics of nautiloidea
- tentacles without suckers
- external shell that can be sealed with hood
water flow in nautiloidea
water enters on either side of the head into the mantle cavity, passes over ctenidia and out through funnel
what facilitates water flow in nautiloidea
muscular contractions of the funnel
which structure is responsible for the gas filled chambers? how does this work?
the siphuncle - replaces fluid within cavities with gas in order to maintain neutral buoyancy
how does the gas in the chambers of Nautilus maintain volume during diel vertical migration?
because of the rigidity of the shell
why do Nautiloids undergo diel vertical migration?
to avoid visual predators
what might be the reason for the adaptations found in squid?
competition with fish
adaptation of shell in squids
reduced to proteinaceous internalized “pen”
what is used for slow swimming in squids
undulation of the fins
what is used to facilitate jet propulsion in squids
muscular pumping of the mantle
how does jet propulsion work in squids?
radial muscles contract, expands mantle cavity and creates area of negative pressure, sucking water in on either side of the head
- circular muscles then contract, forcing the water out through the funnel
what allows the alteration of swimming patterns in squid?
the ability to point the funnel in different directions
which sensory modality is most important for squids as predators?
visual
typical mollusc blood vascular system
oxygenated blood is passed via dorsal blood vessels
- blood percolates through hemal system connective tissue
cephalopod blood vascular system
- branchial heart increases the blood pressure before becoming oxygenated again – increases efficiency
- blood capillaries efficiently deliver oxygenated blood to specific tissues
what is the function of branchial hearts in cephalopods?
act as booster pumps to force blood through gills
what accounts for the high metabolic rate of cephalopods (3)
- ventilation of gills by pumping of muscular mantle
- closed circulatory system - capillary beds
- systemic and branchial hearts
what are chromatophores in cephalopods
pigment-filled cells, rapidly changing colours
what happens to chromatophores when muscles contract?
chromatophores enlarge
