Mollusca Flashcards
Name the 6 larger
groups of which the Phylum Mollusca is a part.
Bilateria, Nephrozoa, Protostomia, Spiralia, Platytrochozoa, Lophotrochozoa.
What 2 groups are potentially the
sister taxon to the Phylum Mollusca?
Sister taxons: Nemertea and Annelida
What are the 6 synapomorphies?
Mantle: tissue secreting calcium carbonate to form the shell; plays a role
Radula: chitinous, toothed, ribbon-like feeding structure to scrape or cutting food
Muscular foot: for locomotion and burrowing
Visceral mass: centralized regions for digestion, excretion, and reproduction
Ctenidia: gills for respiration
Trochophore larva: platonic larval stage
Do all molluscs have gills? How do they function?
No, terrestrial molluscs, like snails and slugs have a pulmonary cavity
instead.
Gills function as water flows over the gills, where lamellae or filaments have cells that allow for diffusion. Water then diffuses into the
blood vessels of the gills, while CO2 diffuses out.
What are the typical life stages of molluscs? (4)
Starts as an egg laid by female molluscs. After fertilization, an embryo
develops. Several larval stages occur.
Trochophore larvae are
free-swimming larvae that has cilia to move and feed.
Veliger larvae have
a foot, mantle, and a reduced shell that is free-swimming. It then
undergoes metamorphosis into a juvenile, which resembles the adult.
Metamorphosis can occur as it settles on a site for sessile adult molluscs.
Do all classes of molluscs have the same stages?
Gastropods have either a trochophore and veliger larval stage, while
bivalves can undergo both. Cephalopods have direct development with no
larval stages.
What functions might these larval stages serve?
Larval stages are responsible for dispersal, moving from the natal area.
Larval stage is the feeding and growth stage as well.
What is so startling about the glochidium stage & exactly where are they found?
Glochidium is the larval stage in freshwater mussels. They are parasitic, attaching to gills and fins of fish. They use hooks to attach to the fish.
Which classes of molluscs have a radula?
Almost all gastropods, most cephalopods, polyplacophra, and scaphopoda
have a radula.
Bivalves don’t have a radula.
What is its
composition?
Radula is made of chitin and
other minerals to be durable. It possesses teeth arranged in rows.
composition? How do the radulae vary between a chiton, snail, & squid?
Chiton have a wide, flat radula with rows of teeth, uniform in structure. It
is simple and not specialized for carnivory.
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Snail radula is highly specialized, with a broad, flattened shape and sharp,
pointed teeth. It distinctly has hook-like teeth for predation.
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Squid radula is reduced, made of fine, backward-facing teeth. They are
compact and specialized to break down food instead of scraping it.
Briefly
describe the foot (in terms of shape & modifications for locomotion & food
procurement) of a chiton, snail, clam and squid.
Chiton have a broad, flat foot to slowly creep and anchor on hard substrate.
Snails have a muscular, flat foot for crawling on mucus.
Clams have a tapered, conical foot to burrow into sediment.
Squids have modified foot in the form of tentacles
and arms for movement, prey capture, and jet propulsion.
Do any molluscs show any evidence of segmentation? (What evidence can you find?) (4)
Chitons exhibit segmentation, as the plates are segmented externally.
They also
have some degree of internal segmentation in their musculature and nervous
system.
Cephalopods are internally segmented in their muscles and nervous
system.
However, gastropods and bivalves do not exhibit segmentation.
Are snails shells sinistral or dextral? At what rank in the hierarchy of the class does
this vary?
Chirality of the coil depends on the species and genetics
dextral snails can have mutants with sinistral coiling in the same species.
How is a snail shell different from the shell of a nautilus?
Snail shells are spiral, solid structures with a single internal cavity. Nautilus shells are chambered, planispiral structure with multiple internal compartments.
While the snail shell is for protection and support, the nautilus shell is used for buoyancy
and protection.
