Lecture 9 - Molluscs

Question 1

2 facts about the group

Answer 1

second largest group of animals

extremely diverse

Question 2

describe their larval stage

Answer 2

similar to annelids - trochophore larvae

Question 3

visceral mass

Answer 3

contains organs and is surrounded by mantle which secretes a shell if they have one

Question 4

where are gills located if they have them and describe gills

Answer 4

in the mantle cavity - gills consist in filaments with cilia causing movement over them

Question 5

foot in molluscs

Answer 5

used for movement but can be modified in many ways - antagonistic muscle contraction in waves

Question 6

circulatory system of basic molluscs

Answer 6

open- haemocoel (blood system +coelom)

Question 7

radula

Answer 7

feeding device located in mouth cavity

Question 8

blood vessels

Answer 8

have a few that open into haemocoel which is surrounded by hemolymph

Question 9

there are 7 groups of molluscs but what are the main 3

Answer 9

gastropods
bivalves
cephalopods

Question 10

what are the 4 main differences of gastropods compared to a standard mollusc

Answer 10

• head with sensory adaptations e.g eyes
• dorso-ventral elongation of body - normally results in coiling of shell and visceral mass
• shell
• torsion - rotation of visceral mass and mantle cavity through 180 degrees

Question 11

what are the 3 advantages of torsion

Answer 11

• protection of larva in marine snails
• protection of adult
• utilisation of oncoming water by gills - gills moved to front of animal

Question 12

disadvantage of torsion

Answer 12

anus over head

Question 13

what is de torsion and how is it proven

Answer 13

• lose shells - to compensate some are brightly coloured or release toxins
• have structures of increase gas exchange
• some species still have a slightly twisted nervous system

Question 14

gastropod symmetry

Answer 14

asymetrical (conispiral) - shifted over one side rather than shell sitting directly on top

Question 15

what are the pulmonates

Answer 15

most specialised gastropods (land snails and slugs) - ditch gills and have a vascularised mantle cavity which they use like a lung

Question 16

main features of bivalves

Answer 16

• laterally compressed

- hinged shell made of two parts

Question 17

describe the head and foot of bivalves

Answer 17

• head and nervous system are reduced with no radula

- foot can be used for feeding but mainly used for anchorage

Question 18

how do most bivalves feed

Answer 18

most are lamellibranchs - filter feeders

Question 19

describe the gills of lamellibranchs

Answer 19

enlarged gills which they generate currents over

- gills are big because they are used for feeding and respiration

Question 20

sex of bivalves

Answer 20

most are dioecious

Question 21

how do bivalves attach to rocks

Answer 21

byssus threads

Question 22

symbiotic relationships in bivalves

Answer 22

with algae for carbon source

Question 23

bivalve eyes

Answer 23

sophisticated eyes very sensitive to light

Question 24

2 facta about cephalopods

Answer 24

• largest invertebrates e.g. giant squid

- most sophisticated molluscs

Question 25

how do cephalopods feed

Answer 25

marine carnivores with a v active lifestyle

Question 26

2 different features of cephalopods compared to other molluscs

Answer 26

• orientation of body changed

- shell is reduced and lost so they evolved other adaptations for protection e.g. ink sak and chromatophores

Question 27

sex of cephalopods

Answer 27

dioecious - separate sexes

Question 28

cephalopod circulatory system

Answer 28

closed - blood vessels throughout the body

Question 29

cephalopod foot

Answer 29

modified into tentacles - muscle contractions to move

Question 30

cephalopod eyes

Answer 30

well developed - similar to mammals - convergent evolution

Question 31

cephalopod hearing

Answer 31

cant hear well - possible adaptation against whales and dolphins that use noise to stun prey

Question 32

cephalopod nervous system

Answer 32

well developed with great cephalisation - can learn

Question 33

cephalopod heart

Answer 33

main heart + 2 accessory hearts - efficient oxygenation as they are active predators

Question 34

describe the nautilus

Answer 34

first appeared in the cambrian but is still found in deep water - lives in chambered shell which act as buoyancy aids - can draw water in or remove it and replace with air - opposite affect on buoyancy

Question 35

what are 3 animals in the class coleoidea and describe their shells

Answer 35

• cuttlefish - internal shell = buoyancy device
• squid - shell reduced to proteinaceous pen
• octopuses - shell is tiny or absent