Mollusca Flashcards
four clades in Mollusca
- Gastropoda
- Placophora
- Bivalvia
- Cephalopoda
main traits found in ALL the clades of Mollusca
- circulation and respiration
- feeding
- reproduction
what is included in Phylum Mollusca
- snails
- slugs
- oysters
- clams
- octopuses
- squids
habitat of Phylum Mollusca
most are MARINE but some are freshwater and terrestrial
describe the body of Mollusca
soft-bodied with most have a hard shell protecting them
key traits in Mollsuc development
- protostome
- bilateral
- triploblastic
- coelomate
ALL molluscs have a similar body plan with THREE main parts
- foot
- visceral mass
- mantle
what are the morphological synapomorphies of phylum Mollusca
- foot
- visceral mass
- mantle
what do MANY (NOT ALL) Molluscs have
- water-filled mantle cavity
- rasp-like radula
visceral mass function
area under the mantle that holds the internal organs
mantle function
found in ALL molluscs and its a tissue that CAN secrete the shell IF the mollusc has one
foot function
aids in locomotion
what makes up the tentacles of octopuses
the foot
are MOST molluscs dioecious or hermaphrodites
dioecious (separate sexes)
where are gonads found
in the visceral mass
what is an exception to most molluscs being dioecious
snails - they are hermaphrodites
habitat of MOST molluscs
marine
what is the second most diverse phylum
Mollusca
what is THE most diverse phylum
insects
four species in Phylum Mollusca
- gastropods
- chitons
- Bivalves
- Cephalopods
habitat of gastropods
marine
do gastropods have a shell (MOST) and if so describe it
yes - single, spiraled shell
most distinctive characteristics of gastropods is
torsion - where the anus and mantle end up ABOVE the head (switched from normal)
when do we see the first evidence of open vs closed circulatory system
in gastropods
closed vs open circulatory system
closed
1. blood is SEPARATE from interstitial fluid
open
1. blood is MIXED with interstitial fluid (now called hemophyl)
2. CANNOT USE THE TERM BLOOD
feeding of gastropods
“grazers”
do gastropods have a complete gut
YES
least to most inclusive
gastropods: Clade Mollusca: Lophotrochozoan: Bilateria: Eumetazoa: Metazoa
what does circulation look like in gastropods
open system of vessels
compare respiration of terrestrial/freshwater and marine gastropods
terrestrial
mantle cavity forms “lungs”
siphon brings in oxygen to the INTERNAL gills
Marine
respiration via gills in the mantle cavity
gills are exposed to the water
marine vs freshwater/terrestrial gastropods reproduction
marine
1. species are dioecious (separate sexes)
2. have complex life-cycle
Freshwater/terrestrial
1. species are hermaphroditic (both sexes in one)
2. direct development
least to most inclusive
Chitons: Phylum Mollusca: Lophotrochozoan: Bilaterian: Eumetazoan: Metazoan
how can one distinguish chitons from other molluscs
their armour made of eight dorsal plates
habitat of chitons
ALL marine
how do chitons use their foot
like a suction cup to grip rock
how do chitons use their radula
to scrape algae off rock surfaces
least to most inclusive
Bivalves: Phylum Mollusca: Lophotorocozoan: Bilaterian: Eumetazoan: Metazoan
Bivalves include
- clams
- oysters
- mussels
- scallops
how did bivalves get their name
they have a shell divided into two halves (valves) held together by very strong adductor muscles
why are bivalves hard to open
their powerful adductor muscles close the shell for protection
what do bivalves use for digging or anchoring
their foot
what are gill used for in bivalves
- feeding
- respiration
- reproduction
are bivalves sessile or motile
most are sessile
how do bivalves feed
they are suspension feeders
suspension feeding
- ciliated gills create water currents
- gills trap fine food-particles in mucus coat
- water flows into the mantle cavity via the incurrent siphon, passes over gills, and exists via the excurrent siphon
how are bivalves, gastropods and chitons all similar
all have open circulation
marine vs freshwater bivalve reproduction
marine
1. mostly dioecious
2. trochophore larvae
Freshwater
1. most are hermaphorditic
2. direct development
what clade of molluscs have glochidia
bivalves
the function of glochidia in bivalves
an immature freshwater mussel life stage modified for a parasitic existence; released larvae may attach to host species and be taken away from parent
do freshwater or marine bivalves have glochidia
SOME freshwater bivalves
least to most inclusive
Cephalopods: Phylum Mollusca: Lophotrochozoan: Bilaterian: Eumetazoan: metazoan
Cephalopods include
- squids
- octopuses
- cuttlefish
- nautiluses
Cephalopods traits
- beak-like jaw surrounded by tentacles
- well-developed sense organs and complex brain
what was modified in Cephalopods to become tentacles
the foot
how do squids swim
use their siphon to fire a jet of water which allows them to swim
how many shelled species make up the Cephalopods
JUST ONE - Nautiluses
how do Cephalopods breath
- water passes in through the in-siphon
- water passes over the gills so the oxygen can be trapped
- water is passed out the out-siphon
what are some examples of well-developed sense organs in Cephalopods
- advanced predatory techniques
- communication (like chromatophores)
- ability to learn
- the unique Cephalopods eye
what are chromatophores in Cephalopods
they are the connection between the brain and the skin via the eye
describe the pattern of neurons in Cephalopods
NOT isolated to the brain, but are spread out through all the arms
describe how the Cephalopods eye can be seen as “better” then vertebrates
they have evolved to LACK a blind spot which can be found in vertebrates
compare squid vs octopus feeding
squid
1. use siphon to fire a jet of water which allows them to swim very quickly and catch prey
octopus
1. creep along the sea floor in search of prey
how do Cephalopods CONTRAST to all the other molluscs
they have a CLOSED circulatory system
reproduction traits of Cephalopods
- dioecious
- direct development (no larvae)
- many are semalparous
- transfer of spermatophore
what does it mean that many Cephalopods are semelparous
reproducing or breeding only once in a lifetime before they die
