Mollusca

Question 1

Mollusca

Answer 1

• Bilateral coelomates
• Open circulatory system (except cephalopods)
• Body covered by epidermal sheet, mantle
  that secretes spicules, sclerites or a shell
• Well defined muscular foot
• Mouth with cuticular teeth (radula)
• Complete gut with regional specialization
• Generally spiral cleavage with trochophore
  larvae

Question 2

Part of the Lophotrochozoa -

Answer 2

small shelly fossils- with annelids, nermertines, phoronids, bryozoans and brachiopods

Question 3

8 Mollusca Classes:

Answer 3

Caudofoveata & Solenogastres, Polyplacophora, Monoplacophora, Scaphopoda, Cephalopoda, Gastropoda, and Bivalvia

Question 4

Caudofoveata & Solenogastres:

Answer 4

Essentially shell-less molluscan worms

Question 5

Polyplacophora:

Answer 5

Chitons

Question 6

Monoplacophora:

Answer 6

Living limpet-like fossils

Question 7

Scaphopoda:

Answer 7

Tusk shells

Question 8

Cephalopoda:

Answer 8

Nautiloids, ammonoids, squids & cuttlefish, octopods, and kin

Question 9

Gastropoda:

Answer 9

Snails and slugs

Question 10

Bivalvia:

Answer 10

Clams, broadly defined (including cockles, mussels, scallops, and oh so many more)

Question 11

The Shell -

Answer 11

• Most molluscs have shell(s) made of calcium carbonate in a protein matrix
  - Aplacophorans have aragonite sclerites
• Secreted by shell glands in the mantle

Question 12

Shell Morphology and Terms -

Answer 12

Slide 7 - 8*

Question 13

Gastropod shells -

Answer 13

• Snails twist into their shells along the central axis, columella
• Shell is typically leaning to the left and coils to the right (dextral)
• The ctenidium, ospharadium, nephridia and heart tend to be reduced

Question 14

Gastropod Torsion -

Answer 14

• Counterclockwise twisting of the visceral mass up to 180° with respect to head and foot during development
  
  • Nervous and digestive systems are twisted, figure 8 config.
  • Mantle cavity moves to over the head

Question 15

Mantle Cavity -

Answer 15

• Lies between mantle and viscera
• Houses the gills, or ctenidia
  - May function only in respiration or also sorts food
• Exit of excretory, digestive and reproductive systems

Question 16

Osphradium-

Answer 16

a chemoreceptor or tactile receptor located adjacent to the ctenidium

Question 17

Gills work through countercurrent exchange –

Answer 17

blood and water flow in opposing directions to enhance gas exchange

Question 18

Circulatory System -

Answer 18

• Cephalopods have a closed system while the rest are open system
  
  • Blood moves through hemocoel in open system that is pumped by a heart
  • Except scaphopods which lack a heart, rely on contractions of the foot

Question 19

Hemoglobin -

Answer 19

With iron (some bivalves and pulmonates)

Question 20

Hemocyanin -

Answer 20

With copper(pulmonates, prosobranchs and cephalopods)

Question 21

Foot -

Answer 21

• Highly variable among the molluscs
• Most form flat, ventral, creeping ciliated sole with mucus glands

Question 22

Locomotion -

Answer 22

• Ciliary gliding
• Pedal waves
• Swimming
• Sucker crawling (cephalopods)

Question 23

Ciliary gliding -

Answer 23

Requires a mucus trail over which the animal glides

Question 24

Pedal waves -

Answer 24

• Muscular contractions of the foot raise and lower sole to cause directional or retrograde waves
  
  • Directional – longitudinal and dorsoventral muscles
  • Retrograde- transverse muscles contract to extend anterior portion

Question 25

Swimming -

Answer 25

Evolved several times, undulations of the body or foot, jet propulsion in cephalopods

Question 26

The Radula -

Answer 26

• Feeding structure in many molluscs
• Ribbons of chitinous teeth produced from radular sac is supported by the odontophore – cartilage-like structure

Question 27

Suspension Feeding -

Answer 27

• Modification of ctenidia (V shaped) to trap particulates through the respiratory current
  
  • Lined with compound cirri, or feeding cilia
• Radula is often reduced, used to pull in mucus, or absent in bivalves
• Labial palps used for particle sorting and rejected particles are called pseudofeces

Question 28

Digestive system -

Answer 28

• Complete, through gut
• Mouth leads to esophagus, then stomach with digestive glands or caeca facilitates extracellular digestion
  
  • Herbivores have a gizzard with teeth to grind up plant matter

Question 29

Crystalline style –

Answer 29

Rod-like matrix lined with digestive enzymes found in autobranch bivalves and some gastropods

Question 30

Cerata –

Answer 30

Extensions of digestive gland in nudibranchs, also used in gas exchange

Question 31

Excretory System -

Answer 31

• Has one or more pairs of kidneys (nephridia)
• Coelomic fluid enters kidney through nephrostome, then into nephridium where selective reabsorption occurs
  
  • Requires pressure filtration, secretion and reabsorption

Question 32

Nervous System -

Answer 32

• Ganglia range from not present in chitons to well developed in cephalopods (forms true brain)
• Major nerve cords run to the mantle (pleural), foot (pedal), gills (parietal), viscera (visceral) and radula (buccal)

Question 33

Sensory Organs -

Answer 33

Tentacles, photoreceptors, statocysts, osphradia and eyes

Question 34

Cephalopod Color and Ink -

Answer 34

• Color and texture of skin used in camouflage and communication
• Pigment cells (chromatophores) expand and contract by muscles at base of the cell to display or hide color

Question 35

Iridocytes -

Answer 35

prismatic cells that reflect or refract light

Question 36

Reproduction -

Answer 36

• Most are gonochoristic with indirect development
• Typically paired gonads with exception of gastropods and cephalopods that have one
• Hermaphroditism present in gastropods, exchange spermatophores during copulation

Question 37

Development -

Answer 37

• Most undergo spiral cleavage
• Indirect development typically has free-swimming trochophore larva, similar to annelids
  
  • Apical tufts and ciliated prototroch
• In gastropods and autobranch bivalves, a second larval stage, the veliger is present