Molluscs (+Brachiopods) Flashcards
what are the names of layers in a mollusc shell?
outer = periostracum (organic)
middle = prismatic (calcium carbonate without magnesium)
inner = nacreous (calcium carbonate with magnesium)
what is the name of the ciliated gas exchange structure used by molluscs?
ctenidium
what features make a mollusc’s gas exchange system effective?
- ciliated
- bipectinate (forked, increases SA)
what feeding structures do molluscs have?
- radula (chitinous invagination of pharynx)
- odontophore (sits underneath radula)
- retractor muscles
- protractor muscles
what structures do molluscs use to move around?
- foot (ventral muscular extension)
- pedal retractor muscles
Gastropods
what shape are gastropods’ shells?
single and spiraled
Gastropods
what is the name of the group of gastropods without a shell?
opisthobranchs (nudibranchs)
Gastropods
what common species are found in Gastropoda?
- limpets (cone shaped shell)
- snails (spiral shell)
- opisthobranchs (nudibranchs)
- ‘sea slugs’ (no shells)
- sea angels
Gastropods
what are the three types of nudibranchs?
what characteristics define each one?
dorid = has gill plume on posterior end of dorsal side
dendronoid = has branched cerata (dorsal projections)
aeonid = has cerata (dorsal projections)
Gastropods
what are the three groups within Gastropoda?
- prosobranchs (have siphons for water entry and osphiradiums) –> sea snails, limpets etc.
- opisthobranchs (lack or have reduced shells) –> nudibranchs
- pulmonata (have land based respiration instead of ctenidia) –> snails, slugs
Gastropods
what unique trait allows cone shells to be effective predators?
barbed radula with toxins and pheromones
Gastropods
describe the pathway of gastropod circulatory systems
- oxygen enters blood stream via ctenidia
- oxygenated blood goes to heart
- heart pumps oxygenated blood into hemocoel
- deoxygenated blood from hemocoel returns to ctenidia
Gastropods
what kinds of nephridia do gastropods have?
- excretory
- reproductive
Gastropods
what disparities do gastropods have?
- well developed heads
- torsion (twisted internal structure)
- shell coiling
Gastropods
what are the axis of symmetry for gastropods?
anterior = mouth end
posterior = anus end
Gastropoda
what feeding techniqiues can a gastropod have?
- grazing
- suction
- drilling
- photosynthesis
- suspension
- toxic harpooning
what three classes have veliger stages after being a trochophore?
- bivalvia
- scaphophora
- gastropoda
describe the veliger larva stage
- has a velum (projected cilliar disc) for swimming and feeding
- develops a mantle shell
- can swim far distances
- develops into adults once settling down
Polyplacophora
what are the common names of polyplacophores?
chitons
Polyplacophora
what is unique about polyplacophore mantles?
made up on 8 plates versus the typical 1
Polyplacophora
what feeding niche do polyplacophores fill?
grazers
Polyplacophora
what disparities do chitons have?
- reduced central nervous system
- has hundreds of small eyes along plates
- no tentacles
Scaphopoda
describe the shell of a scaphopod and how it is used
- long, tubular shell with an opening at the tip
- water enters and exits through the tip
Scaphopoda
how do scaphopods eat?
uses sticky bulbs on feeding tentacles at the foot pick out organic matter in sediment
Scaphopoda
what are the axis of a tusk shell? (up/down/left/right)
pointing up = dorsal
pointing down = ventral
left = anterior (concave)
right = posterior (convex)
Scaphopoda
what disparities do scaphopods have?
- orientation (L/R –> anterior/posterior)
- no ctenidia
Bivalvia
what common species are found in Bivalvia?
- scallops
- clams
- oysters
- mussels
- cockle
what do infaunal and epifaunal mean?
infaunal = buried in sediment
epifaunal = live on top of benthic sediment
Bivalvia
what disparities do bivalves have?
- no head
- no radula (filter feed instead)
- no odontophore
Bivalvia
what are the axis for clams and oysters?
left = left shell (curls to the right)
right = right shell (curls to the left)
ventral = “mouth” opening (far from hinge)
dorsal = hinge side
anterior = shorter outer edge
posterior = longer outer edge (siphon is here)
Bivalvia
what are the axis for mussels?
posterior = wide end
anterior = narrow end
ventral = arched or flat end
dorsal = wide end
left = right of hinge
right = left of hinge
Bivalvia
what are the axis for scallops?
left = facing up
right = facing down
anterior = larger auricle
posterior = smaller auricle
ventral = “mouth” end
dorsal = hinge end
Bivalvia
briefly describe the path of water through a bivalve
water enters via incurrent siphon (ventral) and exits via excurrent siphon (dorsal)
Bivalvia
how do bivalves feed?
- food enters via mucus strings
- labial palps filter through food and directs edible materials into mouth
- after digestion, excretion exits the anus near the excurrent siphon
Bivalvia
what differences in siphons do infaunal and epifaunal bivalves have?
infaunal (buried) = long siphons
epifaunal (above surface) = short siphons
Bivalvia
how do bivalves open and close their shells?
adductor muscles relax = shell opens
adductor muscles contract = shell pulls shut
Aplacophora
what disparities do aplacophores have?
- reduced foot
- reduced mantle (single pair of ctenidia)
- reduced shell (no shell, has spicules)
- reduced head (no eyes/tentacles)
- no specialized sensory/feeding structures
Cephalopoda
what are the axis of a squid?
ventral = arm end
dorsal = fin end
anterior = opposite to funnel
posterior = side with funnel
Cephalopoda
what disparities do cephalopods have?
- highly derived CNS (large brain)
- reduced/lost shell (exception = nautilus)
- foot has become tentacles, funnel and arms
- closed circulatory system
- head is ventral not anterior
- mantle is muscular
Cephalopoda
what do siphuncles do in a nautilus?
maintains buoyancy by regulating gas
Cephalopoda
what structure helps squid and octopus hunt?
chitinous beak on mouth
Cephalopoda
describe the pathway for food in a squid
- mouth
- esophagus
- stomach
- caecum (digestive enzymes here)
- intestines
- anus
Cephalopoda
describe the pathway for blood flow in a squid
- 2 branchial hearts bring deoxygenated blood to ctenidia
- ctenidia sends oxygenated blood to systemic heart
- systemic heart pumps blood to body and returns to branchial hearts
Cephalopoda
how do squids pump water to ctenidia?
muscle contraction (versus cilia current)
Cephalopoda
describe the pathway for sperm in a squid
- produced in testis
- passed through sperm duct (vas deferens)
- seminal vesicle packages sperm into spermatophores (coated with cement body)
- passed to spermatophore sac
- hectodactyl arm pulls spermatophores out for insemination
Cephalopoda
describe the pathway for eggs in a squid
- created in ovary
- passed through ovaduct
- oviducal, nidamental glands package eggs into ribbons
- fertilized eggs secreted out funnel
Brachiopods
how do brachiopods differ from bivalves?
- brachiopod = shells are dorsally/ventrically
symmetrical
bivalves = shells are left/right symmetrical - 2 sets of muscles used to control shells (abductor and adductor) vs one set of bivalves (adductor)
- lophophore used for gas exchange vs ctenidia
