Lecture 10 - Mollusks I

Question 1

Phylum Mollusca:

Answer 1

Free-living invertebrates with an unsegmented, soft body consisting of a visceral mass, foot, mantle, gills, and usually a hard, calcareous, univalved or bivalved shell.

Question 2

Three Important Classes of Phylum Mollusca:

Answer 2

Class Gastropoda
Class Pelecypoda
Class Cephalopoda

Question 3

Class Gastropoda:

Answer 3

Snails, Slugs, & Pteropods

Question 4

Class Gastropoda Geologic Range

Answer 4

Upper Cambrian to Recent

Question 5

Class Pelecypoda:

Answer 5

Clams, Oysters, Scallops, & Mussels

Question 6

Class Pelecypoda Geologic Range

Answer 6

Lower Cambrian to Recent

Question 7

Class Cephalopoda:

Answer 7

Octopus, Squid, Nautiloids, & Ammonoids

Question 8

Class Cephalopoda Geologic Range

Answer 8

Upper Cambrian to Recent

Question 9

Visceral Mass:

Answer 9

Main part of the body containing the vital internal organs

Question 10

Foot:

Answer 10

Muscular organ extending from the visceral mass; it is modified in various molluscan groups as a structure used in swimming, crawling, and/or burrowing.

Question 11

Gills:

Answer 11

Sheets or filaments of blood-filled tissue that serve as respiratory organs.

Question 12

Mantle:

Answer 12

Sheet of tissue that secretes the shell and lines the inside of the shell.

Question 13

Siphon:

Answer 13

Fold in the mantle forming a tubular structure for bringing water into the mantle cavity.

Question 14

Radula:

Answer 14

Rasping, tongue-like structure in the mouth of some mollusks (found in gastropods, cephalopods, & polyplacophores, but not in pelecypods); it is lined with tiny, sharp, tooth-like hard parts for scraping and/or drilling.

Question 15

Molluscan Shell Composition:

Answer 15

Conchiolin (organic material composing the periostracum on the shell surface)
Calcite (may be pure calcite, or else low-Mg or high-Mig calcite)
Aragonite

Question 16

Molluscan Shell Microstructure:

Answer 16

Prismatic, Foliated, Nacreous

Question 17

Prismatic:

Answer 17

Layer consisting of tiny, vertical prisms of calcite or aragonite

Question 18

Foliated:

Answer 18

Layer consisting of imbricated plates of calcite.

Question 19

Nacreous (“mother-of-pearl”):

Answer 19

Interlaminated sheets of aragonite and organic conchiolin.

Question 20

Mollusscan Shell Shape:

Answer 20

Planispiral, Conispiral

Question 21

Planispiral:

Answer 21

Coiled in a single plane (e.g., nautiloids & ammonoids)

Question 22

Conispiral:

Answer 22

Coiled along a translating axis to form a cone (e.g., gastropods)

Question 23

Apex:

Answer 23

Pointed end of the shell

Question 24

Aperture:

Answer 24

Opening in the end of the shell opposite the apex.

Question 25

Radial Ribs:

Answer 25

Raised ridges that radiate from the apex towards the aperture.

Question 26

Growth Rings:

Answer 26

Ring-like ridges that parallel the aperture and represent shell growth.

Question 27

Spines:

Answer 27

Long, sharp projections on the shell exterior.

Question 28

Nodes:

Answer 28

Short, blunt projections on the shell exterior.

Question 29

Class Gastropoda:

Answer 29

Mollusks with a distinct head that usually possesses eyes and sensory tentacles; mouth possesses a radula; foot adapted for crawling in most forms, but is adapted for swimming or burrowing in some forms; nervous system of head & body are distinct; heart has 2 or 3 chambers; general bilateral symmetry, which is secondarily reorganized during ontogeny by “torsion”; most (but not all) members of the class have a single, univalved, conispiral shell with one aperture; the shell is always composed of aragonite; 3 very diverse subclasses

Question 30

Class Gastropoda Geologic Range

Answer 30

Cambrian to Recent

Question 31

Three main subclasses of Class Gastropoda:

Answer 31

Subclass Prosobranchia
Subclass Opisthobranchia
Subclass Pulmonata

Question 32

Subclass Prosobranchia:

Answer 32

Gastropods with gills in front next to head; a robust, external, conispiral shell; commonly have an operculum; very good fossil record

Question 33

Subclass Prosobranchia Geologic Range

Answer 33

Upper Cambrian to Recent

Question 34

Three main orders of Subclass Prosobranchia

Answer 34

Order Archaeogastropoda
Order Mesogastropoda
Order Neogastropoda

Question 35

Order Archaeogastropoda:

Answer 35

Two gills; 3-chambered heart; no inhalent siphon; shell has a circular or oval aperture; mainly herbivores; mostly marine (a few fresh-water species)

Question 36

Order Archaeogastropoda Geologic Range

Answer 36

Upper Cambrian to Recent

Question 37

Order Mesogastropoda:

Answer 37

One gill; 2-chambered heart; well-developed siphon; shell typically has a siphonal notch; includes herbivores, scavengers & predators; exclusively marine

Question 38

Order Mesogastropoda Geologic Range

Answer 38

Lower Ordovician to Recent

Question 39

Order Neogastropoda:

Answer 39

One gill; 2-chambered heart; well-developed siphon; shell typically has a siphonal canal; highly specialized predators; exclusively marine

Question 40

Order Neogastropoda Geologic Range

Answer 40

Upper Jurassic to Recent

Question 41

Subclass Opisthobranchia:

Answer 41

Advanced marine gastropods with gills behind head; either a very thin, internal shell or no shell at all; most are active predators; exclusively marine; typically a very poor fossil record

Question 42

Subclass Opisthobranchia Geologic Range

Answer 42

Middle Devonian to Recent

Question 43

Subclass Pulmonata:

Answer 43

Advanced terrestrial gastropods with either a thin external shell or no shell at all; mantle adapted for breathing in air; mainly herbivores; continental environments; a very spotty fossil record found only in terrestrial sediments

Question 44

Subclass Pulmonata Geologic Range

Answer 44

Pennsylvanian to Recent

Question 45

Visceral Mass:

Answer 45

Torsion brings the stomach up and over the head

Question 46

Foot:

Answer 46

Muscular organ modified mainly for crawling, but also for swimming and/or burrowing.

Question 47

Gills:

Answer 47

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

Question 48

Mantle:

Answer 48

Tissue that lines inside of shell of prosobranchs or envelopes shell of opisthobranchs.

Question 49

Siphon:

Answer 49

Fold in the mantle forming a single inhalent tube.

Question 50

Radula:

Answer 50

Rasping, tongue-like structure in the mouth of all gastropods.

Question 51

Protoconch:

Answer 51

Earliest portion of the shell, located at the apex.

Question 52

Whorl:

Answer 52

One complete revolution of the conispiral shell.

Question 53

Columella:

Answer 53

Pillar of shell material at the axis of coiling of the shell.

Question 54

Aperture:

Answer 54

Large opening in the shell through which the foot protrudes.

Question 55

Callus:

Answer 55

Thickened region of the shell along the inside margin of the aperture.

Question 56

Lip:

Answer 56

Thickened region of the shell along the outside margin of the aperture.

Question 57

Operculum:

Answer 57

Calcareous or chitinous “door”, which seals off the aperture when the foot retracts.

Question 58

Anal Slit:

Answer 58

Notch in the lateral side of the aperture (only in pleurotomariids & some primitive limpets) to accommodate excretion from the anus.

Question 59

Anal Aperture:

Answer 59

Second opening in apex of some limpets to accommodate excretion from the anus.

Question 60

Siphonal Notch:

Answer 60

Notch in the anterior end of the aperture of most mesogastropods to allow the siphon to protrude.

Question 61

Siphonal Canal:

Answer 61

Groove-like or tubular extension of the notch in the anterior end of the aperture of most neogastropods to conceal and protect the long siphon as it protrudes.

Question 62

Ornamentation:

Answer 62

Ribs, spines, nodes, etc., on the exterior of the shell.