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Earth history and life - 29202 > Molluscs part 1 - Bivalves > Flashcards

Molluscs part 1 - Bivalves Flashcards

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1
Q

What is the age extent of Phylum Mollusca?

A

Cambrian to recent

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2
Q

How many species are part of phylum Mollusca?

A

> 120,000 species

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3
Q

What environment are molluscs found in?

A

Typically marine (although some Bivalve and Gastropods freshwater/ terrestrial)

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4
Q

How many groups can phylum Mollusca be split into?

A

9

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5
Q

What are the 9 groups of mollusca?

A

Aplacophora
Polyplacophora
Monoplacophora
Helcionelloida
Gastropoda
Cephalopoda
Lamellibranchia/Pelycopoda/Bivalvia
Rostroconchia
Scaphopoda

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6
Q

What are some examples of how big Molluscs can get?

A

Architeuthis >10m in length
Mesonychoteuthis hamiltoni >13m in length

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7
Q

What is the structure of molluscs like?

A

generally unsegmented
serial repetition of internal organs
often with external or secondary internal
skeleton of CaCO3 (Aragonite)

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8
Q

What is the Radula for molluscs?

A

Composed of chitin and is multiple teeth which act as a rasping feeding organ

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9
Q

What is the basis of the Archimollusc concept?

A

hypothetical ancestor for all molluscs
consider morphology of all other molluscs
and how they relate to ‘archimollusc’

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10
Q

What is the shell of the Archimollusc like?

A

cap-like secreted by the mantle

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11
Q

How are the anus and mouth positioned on the Archimollusc?

A

Mouth and anus at separate ends
The anus opens into the mantle cavity which acts as waste outlet

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12
Q

Where is the visceral mass of the Archimollusc located?

A

Above the mantle cavity

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13
Q

What does the diversification of molluscs from the Archimollusc link to?

A

Changes in mode of life and feeding

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14
Q

What does the Archimollusc share characteristics with most?

A

Tergomya (monoplacophorans) and Polyplacophorans (chitons)

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15
Q

What is the feeding and movement of gastropods, polyplacophorans and
tergomya?

A

Slowly move on a muscular foot
Radula in mouth (scavengers, herbivores and active predators)

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16
Q

What is the main type of feeding of bivalves?

A

predominately deposit feeders (rarely
suspension feeders)

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17
Q

What is not present in bivalves?

A

No head,
No jaws
limited capacity for locomotion

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18
Q

What type of feed gathering is done by cephalopods?

A

Predatory

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19
Q

How has the radula of cephalopods evolved to be predatory?

A

Ability to swallow and specialised jaws which can slice and chop

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20
Q

What does the head contain/ allow for in cephalopods?

A

sense organs and brain
buoyancy, locomotion, tentacules

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21
Q

What is the bivalve the only common mollusc to have?

A

2 valves shells

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22
Q

How are the valves split with bivalves and how are they connected?

A

Left and right
With a connecting ligament

23
Q

How do you determine what side of a bivalves you have?

A

The side of the pallial sinus is
(left of shell is left)

24
Q

What is the plane of symmetry for bivalves?

A

Passes between the valves (leading to relative equivalved nature)

25
Q

What is the unexplained dominance split between brachiopods and bivalves?

A

brachiopods dominate Palaeozoic
bivalves in Mesozoic and Cenozoic

26
Q

What environment are mot Lamellibranchia/Pelycopoda bivalves?

A

Marine (some freshwater)

27
Q

What is the mode of life of almost all Lamellibranchia/Pelycopoda bivalves?

A

Benthic

28
Q

What is the characteristic mode of life for Lamellibranchia/Pelycopoda bivalves?

A

infaunal burrowers though many are epifaunal

29
Q

What is one of the characteristics features of Lamellibranchia/Pelycopoda bivalves?

A

Enlarged gills which extend from body into the mantle cavity

29
Q

What are the enlarged gills of Lamellibranchia/Pelycopoda bivalves used for?

A

filter food and respiration

30
Q

What is the anatomy of Lamellibranchia/Pelycopoda bivalves?

A

Gut is dorsal
Mouth at anterior
Anus at posterior
Muscular foot used in burrowing
Cilia cover gills
Siphons

31
Q

What is the purpose of the cilia covering gills in Lamellibranchia/Pelycopoda?

A

generate water current

32
Q

How is water drawn in and expelled from Lamellibranchia/Pelycopoda?

A

Water in through inhalent siphon
Filtering expelled out exhalent siphon

33
Q

What is the shell structure of bivalves?

A

Three layer structure

34
Q

What are the layers of bivalves?

A

Outer layer organic periostracum
Two inner layers of CaCO3

35
Q

How are the valves of bivalves opened and closed?

A

Elastic ligament open valves
Adductor muscles close valves

36
Q

What are isomyarian adductor muscle scars?

A

Equal in size

37
Q

What are anisomyarian adductor muscle scars?

A

Unequal in size

38
Q

What are monomyarian adductor muscle scars?

A

Single muscle present

39
Q

What is does the pallial line do?

A

Connects muscle scars

40
Q

What does the pallial line mark?

A

Where the inner most of two calcareous shell layers end

41
Q

What is the pallial sinus?

A

Where the pallial line is indented posteriorly

42
Q

What is the pallial sinus an indicator of?

A

A pocket which siphons are retracted into

43
Q

What are the characteristics of infaunal bivalves?

A

Typically equivalved
Isomyarian/ weakly anisomyarian
Resist shearing forces
Pallial sinus

44
Q

What happens to characteristics of infaunal bivalves as you get deeper into burrowing?

A

Gapes
Elongated shells (linked to speed of burrowing)

45
Q

What will the shell of epifaunal byssally attached?

A

Shell flattened

46
Q

What are some examples of epifaunal byssally attached bivalves?

A

Mytilus
Plagiostoma

47
Q

What are the characteristics of epifaunal cemented bivalves?

A

Strongly
Anisomyarian or monomyarian
Irregular
One shell greatly thickened

48
Q

What is an example of epifaunal cemented bivalves?

A

Ostrea

49
Q

What are the characteristics of epifaunal free living bivalves?

A

monomyarian
or
equilateral symmetry

50
Q

What are some examples of epifaunal free living bivalves?

A

Gryphaea
or
Scallop

51
Q

What do boring bivalves do?

A

Bore into hard substances (abrasive shell)

52
Q

What is an example of a boring bivalve?

A

Petricola or Teredo

Earth history and life - 29202 (29 decks)

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