Molluscs part 1 - Bivalves

Question 1

What is the age extent of Phylum Mollusca?

Answer 1

Cambrian to recent

Question 2

How many species are part of phylum Mollusca?

Answer 2

> 120,000 species

Question 3

What environment are molluscs found in?

Answer 3

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

Question 4

How many groups can phylum Mollusca be split into?

Answer 4

9

Question 5

What are the 9 groups of mollusca?

Answer 5

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

Question 6

What are some examples of how big Molluscs can get?

Answer 6

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

Question 7

What is the structure of molluscs like?

Answer 7

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

Question 8

What is the Radula for molluscs?

Answer 8

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

Question 9

What is the basis of the Archimollusc concept?

Answer 9

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

Question 10

What is the shell of the Archimollusc like?

Answer 10

cap-like secreted by the mantle

Question 11

How are the anus and mouth positioned on the Archimollusc?

Answer 11

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

Question 12

Where is the visceral mass of the Archimollusc located?

Answer 12

Above the mantle cavity

Question 13

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

Answer 13

Changes in mode of life and feeding

Question 14

What does the Archimollusc share characteristics with most?

Answer 14

Tergomya (monoplacophorans) and Polyplacophorans (chitons)

Question 15

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

Answer 15

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

Question 16

What is the main type of feeding of bivalves?

Answer 16

predominately deposit feeders (rarely
suspension feeders)

Question 17

What is not present in bivalves?

Answer 17

No head,
No jaws
limited capacity for locomotion

Question 18

What type of feed gathering is done by cephalopods?

Answer 18

Predatory

Question 19

How has the radula of cephalopods evolved to be predatory?

Answer 19

Ability to swallow and specialised jaws which can slice and chop

Question 20

What does the head contain/ allow for in cephalopods?

Answer 20

sense organs and brain
buoyancy, locomotion, tentacules

Question 21

What is the bivalve the only common mollusc to have?

Answer 21

2 valves shells

Question 22

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

Answer 22

Left and right
With a connecting ligament

Question 23

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

Answer 23

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

Question 24

What is the plane of symmetry for bivalves?

Answer 24

Passes between the valves (leading to relative equivalved nature)

Question 25

What is the unexplained dominance split between brachiopods and bivalves?

Answer 25

brachiopods dominate Palaeozoic bivalves in Mesozoic and Cenozoic

Question 26

What environment are mot Lamellibranchia/Pelycopoda bivalves?

Answer 26

Marine (some freshwater)

Question 27

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

Answer 27

Benthic

Question 28

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

Answer 28

infaunal burrowers though many are epifaunal

Question 29

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

Answer 29

Enlarged gills which extend from body into the mantle cavity

Question 29

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

Answer 29

filter food and respiration

Question 30

What is the anatomy of Lamellibranchia/Pelycopoda bivalves?

Answer 30

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

Question 31

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

Answer 31

generate water current

Question 32

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

Answer 32

Water in through inhalent siphon Filtering expelled out exhalent siphon

Question 33

What is the shell structure of bivalves?

Answer 33

Three layer structure

Question 34

What are the layers of bivalves?

Answer 34

Outer layer organic periostracum Two inner layers of CaCO3

Question 35

How are the valves of bivalves opened and closed?

Answer 35

Elastic ligament open valves Adductor muscles close valves

Question 36

What are isomyarian adductor muscle scars?

Answer 36

Equal in size

Question 37

What are anisomyarian adductor muscle scars?

Answer 37

Unequal in size

Question 38

What are monomyarian adductor muscle scars?

Answer 38

Single muscle present

Question 39

What is does the pallial line do?

Answer 39

Connects muscle scars

Question 40

What does the pallial line mark?

Answer 40

Where the inner most of two calcareous shell layers end

Question 41

What is the pallial sinus?

Answer 41

Where the pallial line is indented posteriorly

Question 42

What is the pallial sinus an indicator of?

Answer 42

A pocket which siphons are retracted into

Question 43

What are the characteristics of infaunal bivalves?

Answer 43

Typically equivalved Isomyarian/ weakly anisomyarian Resist shearing forces Pallial sinus

Question 44

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

Answer 44

Gapes Elongated shells (linked to speed of burrowing)

Question 45

What will the shell of epifaunal byssally attached?

Answer 45

Shell flattened

Question 46

What are some examples of epifaunal byssally attached bivalves?

Answer 46

Mytilus Plagiostoma

Question 47

What are the characteristics of epifaunal cemented bivalves?

Answer 47

Strongly Anisomyarian or monomyarian Irregular One shell greatly thickened

Question 48

What is an example of epifaunal cemented bivalves?

Answer 48

Ostrea

Question 49

What are the characteristics of epifaunal free living bivalves?

Answer 49

monomyarian or equilateral symmetry

Question 50

What are some examples of epifaunal free living bivalves?

Answer 50

Gryphaea or Scallop

Question 51

What do boring bivalves do?

Answer 51

Bore into hard substances (abrasive shell)

Question 52

What is an example of a boring bivalve?

Answer 52

Petricola or Teredo