mollusca Flashcards

1
Q

Mollusca characteristics

A
  • Second biggest group of marine organisms
  • Fossilise well
  • adapted to every kind of habitat in marine systems
  • Most abundant class = gastropods, bivalvia
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2
Q

Mollusca physical characteristics

A
  • ventral
  • dorsal
  • mantle
  • radula
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3
Q

what is the ventral in molluscs

A

muscular foot
- contains nervous units
- can be used for swimming, digging, holding on, or capturing prey; missing only in Caudofoveata)

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4
Q

what is the dorsal in molluscs

A

visceral mass containing internal organs

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5
Q

what is the mantle in molluscs

A
  • sheet of tissue covering all or part of the body -> creates a space between it and the visceral mass (mantle cavity) - includes epidermis secreting the calcium carbonate shell
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6
Q

what is the radula in molluscs

A
  • rasping organ containing a ribbon of chitin covered in rows of backwards-facing teeth with a moveable, fleshy base
  • as teeth wear out, they are replaced by new rows from behind (lack in all bivalves and some gastropods)
  • can be heavily modified
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7
Q

what type of circulatory system do molluscs have

A
  • Open circulation (except cephalopods)
  • blood travels freely in spongy sinuses which surround it
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8
Q

class gastropods characteristics

A
  • All snails and slugs
  • Head usually well-developed, with sensory appendages
  • Large, muscular foot
  • All show, to some degree, torsion – body has twisted so that the anus is now above the head
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9
Q

2 different types / subclasses of gastropods

A
  1. Prosobranchs
  2. Opisthobranchs (all have reduced shell)
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10
Q

Prosobranch characteristics

A

e.g. abalone, littorinids, whelks, heteropods
- Vast majority of marine snails (include heteropods)
- Mostly herbivorous - although some carnivores
- Important grazers e.g. macroalage - live on their food source
- Feed using radula

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11
Q

what are heteropods

A
  • ancient group of pelagic snails
  • Usually warm water
  • Foot is a laterally flattened, ventral fin
  • Shell generally reduced or absent
  • Active carnivores
  • Telescopic eye – may be better than a fish’s
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12
Q

orders within Opisthobranch

A
  • Order Thecosomata - shelled pteropods
  • Order Gymnosomata - naked pteropods
  • Order Nudibranchia - sea slugs
    gills usually absent - exchange gas across body surface
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13
Q

Order Thecosomata characteristics

A
  • Foot modified into pair of wings to move
  • Suspension feeders
  • Trap food particles in mucous covered parapodia /mucous nets
  • Play important ecological role – produce membrane bound faecal pellets that sink fast / export carbon to deep ocean when they die – help with ocean acidificaton

TGN

theco = thick (shelled)

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14
Q

Order Gymnosomata characteristics

A
  • naked pteropod - Lack shell and mantle cavity
  • Streamlined, pair of wings near head
  • Hooks, teeth and adhesive tentacles (cephaloconi) or Tentacle bearing suckers (acetabula)
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15
Q

Order Nudibranchia characteristics

A
  • Bilaterally symmetrical (secondary detorsion)
  • Grazing carnivores
  • Feed on sessile organisms e.g. corals, sponges
  • Each family restricted to one type of prey
  • Dorsal surface often has projections called cerata (Involved in gas exchange)
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16
Q

what do molluscs with no shell use for defence e.g. Gymnosomes and Nudibranchia

A
  • Primary motor of defence = camoflage
  • Chemical defence = toxins (synthesised by the slug / taken from prey – stolen nematocysts = kleptocnidae)
17
Q

family conidae characteristics e.g dog whelk

A
  • Cone shells
  • Ones that eat fish have hollow harpoon connected to venom gland – contain neurotoxins to kill the fish
18
Q

dog whelk characteristics (family conidae)

A
  • mainly barnacles and mussels, also other bivalves and gastropods
  • Important intertidal predator
  • Mouth and radula on an extensible proboscis - radula modified to bore holes in shells
  • Accessory Boring Organ on the sole of the foot secretes a shell -softening chemical
  • Once penetrated, the prey is narcotised before the whelk secretes digestive enzymes into the body of the prey - then ingests the resultant tissue ‘soup’
19
Q

class bivalve characteristics

A

clams, oysters, mussels, etc.
- Shell of two halves (valves) - hinged dorsally by calcified teeth + tough ligament which springs the shell open / Shell held closed by adductor muscles
- Dominated by lamellibranchs
- siphons in burrowing species
- Muscular foot often used for digging
- Large gills (ctenidia) - gas exchange + food collection

20
Q

blue mussel characteristics (class bivalve)

A

Foot is reduced and used to attach byssal threads to substratum

21
Q

Class Polyplacophora (chitons) characteristics

A
  • Ovoid / dorso-ventrally flattened
  • Shell divided into 8 overlapping plates
  • Use foot to move like a snail
  • Commonly intertidal
  • Move and feed at high tide
  • Gills for gas exchange
22
Q

what are the large gills called in bivalves

A

ctenidia

23
Q

what are stollen nematocysts called

A

kleptocnidae

24
Q

what are the tentacle characteristics called that Order Gymnosomata have

A

adhesive tentacles (cephaloconi) or Tentacle bearing suckers (acetabula)