Mollusca Flashcards
phylum mollusca
second most species-rich phylum.
-mostly marine, some freshwater & terrestrial.
9 common to most mollusca
- small eucoelom + large haemocoelic circulatory system
- chambered heart
- dorsal body wall with thick epidermal layer = mantle
- glands in mantles create calcareous shell
- ventral body wall muscles develop as muscular foot for crawling, digging
- radula for feeding - toothed, rasping
- complex gut
- gas-exchange systems - ctenidia.
- excretory system includes metanephridia
two types of fluid-filled cavities within the mesoderm
small eucoelom - arises via schizocoely.
hemocoel extensive - blood pumped through short vessels that open into spongy tissues. “open” circulatory system & hydraulic skeleton
2 main clades of extant mollusca
aculifera
conchifera
aculifera - 3 classes within
- small calcareous sclerites into mantle.
polyplacophora
caudofoveata
solenogastres
conchifera - 5 classes within
- most of body covered in one or two large shells
monoplacophora gastropoda bivalvia cephalopoda scaphopoda
mollusc: shells - what order doesnt have shell?
what are three layers?
aplacophoran doesnt have shell. (others may have lost independently)
- periostracum (tough protein) - prismatic (chalky calcareous layer - thickest)
- nacreous layer (shiny, smooth inner layer)
how do pearls form?
pearls form when irritant gets into mantle of a valve, secretes nacre around it to wall it off
mollusc: ctenidia - structures
multi-leaved gills in mantle cavity.
long flattened central axis bearing two haemolymph vessels & ciliated lamellae
mollusc: ctenidia - principle function
gas-exchange: deoxygenated flows thru efferent vessel, rough lamellae where they pcik up O2, back to body cavity via afferent vessel.
– also used for collecting food particles
mollusc :sensory organs (4)
eyes: evolved independently in different lineages; absent, simple, image-forming
statocyst: in conchifera
- tentacles: slim extensions used for touch + chemoreception
- ospharidium: path of chemosensory tissue, near gills
mollusc: reproduction
highly variable.
- mostly separate sexes, sometimes hermaphroditism.
- dertilization mostly external except cephalopoda, gastropoda.
- development indirect with trocophore (sometimes veliger) larva
aculifera
- clade aplacophora = 2 classes
- 3 classes in aculifera
caudofoveata (aplac)
solenogastres (aplac)
lat, polyplacophora = aplacophora
featuers of aplacophora
completely lack shell plates. pointy calcareous spicules in their mantles. small, marine, benthic, burrowers, lack eyes & metanephridia
class caudofoveata - clade?
aplacophora
- no foot.
- do have radula. one pair of ctenidia. no visceral hump. separate sexes
class solenogastres - clade?
no ctenidia, some species lack radula.
- small foot that can be retracted. sequentially hermaphroditic. trocophore
class polyplacophora - clade? common name? defining feature; other features.
clade: aculifera
common name: chitons
defining feature: 7-8 flat dorsal shell plates.
8 pedal retractors, many ctenidia. poor head, lack eye. powerful foot.
repro in polyplacophora
sexes separate, fertilization external.
egg shed in gelatinous string.
indirect development with trocophore larva
conchifera - 4 shared features
shell univalve
shell of basically three layers
statocysts
viscera concentrated dorsally.
class monoplacophora - clade?
- known from?
- mollusc features?
clade conchifera. known from fossils from cambrian. lack eyes, have foot , radula, 3-7 metanephridia ,3-6 pairs of ctenidia
hypothesis about missing link btw segmented worms and mollusca?
monoplacophora
-phylogenetic analyses doesn’t lace monoplacophora to annelids.
class gastropoda - clade? - internally asymmetrical
clade conchifera
- asymmetrical with single typically spiral shell into which the body can be withdrawn
7 features of shells 1 aperture 2 - columella 3- whorl 4- body whoel 4 - spire 5 - protoconch 6- spire 7 - operculum
1 opening through which the shell spiral 2 main axis which shell spirals around 3 each turn of the shell 4 spin up the shell 5 apex of shell represents larval shell 6 flat plate on dorsal side of foot; close shell when withdraw body.
gastropoda - gill form varies
bipectinate, unipectinate, leaf-like or no gill.
anteriorally (prosobranch) or posteriorally (opisthobranch). - lack ctenidia = pulmonate, lung-like region. opening to lung is pneumostome.
locomotion in gastropods
swim by flapping extensions of foot. or move with crawling.
crawling = need special pedal mucus.
2 waves of foot when moving - gastropods
direct waves: waves in same direction as movement.
retrograde wave: opposite direction from movement.
move slowly vs quickly - mucus consistency
slowly = sticky quickly = slippery
gastropod feeding
rasping using radula on algae.
can peirce, drill, harpoon - depending on radula shape
gastropod reproduction
some separate sex, some herm.
some free spawn, most have internal fertilization + copulate.
terrestrial have calcareous love darts
gastropod development
protostome development, trochophore larva. veliger larve (foot, shell, operculum)
torsion: visceral mass an mantle rotate in veliger stage. asymmetries in body, twist in gut. maybe assist in operculum closing over the foot.
nudibranchs
- feed on ? phenomenon?
shell-less gastropods.
feed on cnidarians.
- kleptocnidae: consume cnidae but inhibit firing. can fire when threatened by predator
– cerata: wheere cnidae stored
cone snails - radula
harpoon-like stylets. stabbing, hauling, inject venom that paralyzes victim
class bivalvia - features uniting?
valve shell, loss of radula, lateral compression of body, adductor muscles, ligament.
bivalvia - other features that most have
head reduced, lack eyes + tentacles. filter-feeding + gas-exchange ctenidia. bbyssal threads to attach to substrates. foot modified for burrowing. mantle often modified into tubular siphons
bivalve shell structures
umbo: juvenile shell, dorsal
proteinaceous hinge ligament
one or two adductor muscles present. - contract = close, outer ligament stretched. adductor relax - outer ligament contract.
- hinge has teeth for corresponding slots
gill structure and function in bivalves
- protobranch: small and mainly respiratory.. live in soft marine sediments. feed using labial palps. palp proboscis. low density, hence organic - to mouth.
-lamellibranch = filter feeding and gas exchange. v = demibranch. ctenidial filaments are long and folded on themselves.
2 types of lamellibranch gills
filibranch: adjacten gill filaments loosely attached to each other by tufts of cilia.
pteriomorpha
- eulamellibranch: adjacent gill filaments attached to each other by bridges of solid tissue.
feeding in bivalves
using lamellibranch.
- frontolateral cilia flick particles to filament.
- particles moved by frontal toward demibranch groove.
palps sort thru particles.
rejected particles accumulate till she reaches a sizable mass, ejected as pseudofeces
burrowing in bivalves
shell + foot acting as alternating anchors
byssal thread and cement in bivalves
liquid in byssal gland. extruded, when in contact with sea water = thread. clue to hard substrate
reproduction + development in bivalves
marine: spawned freely.
freshwater: inhaled by female, internal fertilization.
- most have trocophore larva.
glochidia = larva modified to parasitize
cephalopoda
squid, nautilus. marine.
pelagic, shell reduced. arms, tentacles, funnel from head + foot.
groups within cephalopoda
palcephalopoda - nautilidia
neocephalopoda - ammonoidea, coleoidea = octopodiformes, decapodiformes
circulatory systems
- nautiluses ctenidia?
2 pairs of ctenidia. other cephalopods only 1 pair.
- need lots of o2 bc active. centralized heart.
decapodiformes = closed circulatory system.
shells in cephalopodds.
nautilus, whorls with septa/chambers throughout. connected via siphuncle filled with tube to mediate gas in there + buoyancy.
squids + cuttlefish = pen + cuttle bone.
octopuses have no shell. extenct has shells.
locomotion in cephalopods
contract radial muscles to sunk in water, contract circular muscles to squirt water out thru funnel for jet propulsion.
colours and ink in cephalopods
change colour rapidly bc chromatophores
- each cell has muscle, contract or expand. expand = pigment displayed. camouflage.
ink as defense, mask escape
eyes in cephalopoda
image-forming.
retinal axons out the back. no otpic nerve/blind spot
feeding in cephalopoda
carnivorous except vampire squid.
radula and chitinous beak.
reproduction and development in cephalopoda
separate sexes, courtship complex. coputation. male uses arm called hectocotylus to transfer spermatophores
eggs in strings/tough case.
direct development
class scaphopoda
tusk shell, marine. reduced head, tenidia, eyes ,heart. cylindrical foot fot digging. live in sediment. water exchange thru posterior opening.
sticky bulbous tips called captacula
sexes separate, fertilization external.
have trocophore + veliger larva.
