Lecture 12 - Mollusks II

Question 1

Class Pelecypoda:

Answer 1

Mollusks without a distinct head, radula, or any anterior sensory apparatus; foot adapted for burrowing in most forms, but is adapted for crawling in some forms, and is functionless in others; poorly developed nervous system; general bilateral symmetry (they do not undergo “torsion”); have a hinged, bivalved shell with the symmetry plane oriented between the two valves, which are mirror images of each other; the shell is usually composed entirely of calcite, but some forms have a shell composed entirely of aragonite, and a few forms have a shell that is mostly calcite with an interior lining of nacreous aragonite; 5 diverse subclasses with excellent fossil records

Question 2

Class Pelecypoda Geologic Range

Answer 2

Early Cambrian to Recent

Question 3

Five main subclasses of Class Pelecypoda

Answer 3

Subclass Palaeotaxodonta
Subclass Isofilibranchia
Subclass Heteroconchia
Subclass Pteriomorpha
Subclass Anomalodesmata

Question 4

Subclass Palaeotaxodonta:

Answer 4

Pelecypods with protobranch gills; shell usually aragonite with nacreous microstructure; dentition usually taxodont, but some are actinodont; usually isomyarian; no siphons; foot adapted for burrowing or crawling

Question 5

Subclass Palaeotaxodonta Geologic Range

Answer 5

Early Cambrian to Recent

Question 6

Subclass Isofilibranchia:

Answer 6

Pelecypods with filibranch gills; shell either calcite + aragonite or totally aragonite with a nacreous interior; dentition usually absent or functionless; usually isomyarian; no siphons; small, functionless foot

Question 7

Subclass Isofilibranchia Geologic Range

Answer 7

Early Cambrian to Recent

Question 8

Subclass Heteroconchia:

Answer 8

Pelecypods with filibranch or eulamellibranch gills; shell usually aragonite with variable microstructure; dentition usually heteroodont, but some are taxodont; usually isomyarian; most have siphons; foot adapted for burrowing in most forms, crawling in some

Question 9

Subclass Heteroconchia Geologic Range

Answer 9

Early Ordovician to Recent

Question 10

Subclass Pteriomorpha:

Answer 10

Pelecypods with filibranch or eulamellibranch gills; shell may be aragonite, calcite or both, with variable microstructure, dentition may be heteroodont, taxodont, actinodont or absent; usually anisomyarian; most do not have siphons; small, functionless foot

Question 11

Subclass Pteriomorpha Geologic Range

Answer 11

Early Ordovician to Recent

Question 12

Subclass Anomalodesmata:

Answer 12

Pelecypods with eulamellibranch or septibranch gills; shell is aragonite with prismatic microstructure on the outside and nacreous microstructure on the inside; dentition usually absent; usually isomyarian; most have siphons; small, foot adapted for burrowing

Question 13

Subclass Anomalodesmata Geologic Range

Answer 13

Middle Ordovician to Recent

Question 14

Visceral Mass:

Answer 14

Headless mass is positioned in the hinge region of the shell interior

Question 15

Foot:

Answer 15

Muscular organ modified mainly for burrowing

Question 16

Labial Palps:

Answer 16

Pair of fleshy structures adjacent to the mouth; used for feeding

Question 17

Mantle:

Answer 17

Tissue that lines the inside of the pelecypod shell

Question 18

Siphon:

Answer 18

Folds in the mantle forming two tubes, including one inhalent and one exhalent siphon.

Question 19

Gills:

Answer 19

Variably-shaped structures of blood-filled tissue that serve as respiratory organs.

Question 20

Adductor Muscles:

Answer 20

Muscles that flex to close the two pelecypod valves.

Question 21

Isomyarian:

Answer 21

Equal-sized anterior and posterior adductors

Question 22

Anisomyarian:

Answer 22

Small anterior adductor and large psterior adductor

Question 23

Monomyarian:

Answer 23

Only one adductor muscle (the posterior adductor)

Question 24

Ligament:

Answer 24

Connective tissue holding the valves together at the hinge (either external or internal)

Question 25

Beak (=Umbo):

Answer 25

Pointed end of the shell, near the hingeline

Question 26

Commissure:

Answer 26

Site where the two valves meet opposite the beak when the shell is closed.

Question 27

Right Valve vs. Left Valve

Answer 27

The two valves are mirror images of each other

Question 28

Anterior:

Answer 28

end of the shell towards which the beak points

Question 29

Posterior:

Answer 29

end away from beak

Question 30

Dorsal:

Answer 30

hinge side of shell

Question 31

Ventral:

Answer 31

commissure side of the shell

Question 32

Ornamentation:

Answer 32

Radial ribs, growth rings, spines, etc., on the exterior of the shell

Question 33

Adductor Scars:

Answer 33

Lines on the shell interior marking where the adductor muscles attach

Question 34

Pallial Line:

Answer 34

Line on the shell interior along which the mantle attaches.

Question 35

Pallial Sinus:

Answer 35

Indentation of the pallial line marking where the siphons are positioned.

Question 36

Hinge Dentition:

Answer 36

Tooth and socket structure that articulates the two valves together.

Question 37

Cardinal Teeth:

Answer 37

Short hinge teeth that are oriented roughtly perpendicular to the hingeline.

Question 38

Lateral Teeth:

Answer 38

Long hinge teeth that are oriented roughly parallel to the hingeline.