9. General Characteristics
Most versatile body plan of all animals
- Divided into 8 classes
- Most diversity is in two (Gastropoda and Bivalvia)
- Microscopic to 20m in length
- Most are less than 10 cm
- Sessil to fast swimmers
- Occupy marine, fresh, and terrestrial biospheres
- Only Gastropoda and Bivalvia in freshwater
- Only gastropoda in terrestrial areas
- Must be moist and with calcium in soil
10. General Characteristics
Form and Function
- Despite wide variety of body plans, some basic features shared
- Mantle - secretes shell (or becomes outer body covering)
- Visceral mass - most internal organs (embedded in tissue)
- Shell - external or internal
- Radula - specialized feeding organ
- Foot - used for locomotion
12. General Characteristics
Body in two parts
- Head-foot
- More active region of a mollusc
- Contains feeding, sensory, and locomotor organs
- Radula - tongue-like rasping organ
- Present in all except bivalves and solenogastres
- File-like, may have 250,000 teeth
- New teeth continually produced
- Supported on cartilage-like rod - odontophore
- Works like a conveyor belt to deliver food to digestive tract
15. General Characteristics
Body in two parts
- Head-foot
- Foot is present in all molluscs (used for
locomotion)
- Creeping movements
- Slime trail
- Digging
- Attachment
- Byssal threads
- For some, modified into proboscis
16. General Characteristics
Body in two parts
- Head-foot
- Foot is present in all molluscs (used for
locomotion)
- Creeping movements
- Slime trail
- Digging
- Attachment
- Byssal threads
- For some, modified into proboscis
17. General Characteristics
Body in two parts
- Head-foot
- Foot is present in all molluscs (used for
locomotion)
- Creeping movements
- Slime trail
- Digging
- Attachment
- Byssal threads
- For some, modified into proboscis
18. General Characteristics
Body in two parts
- Head-foot
- Foot is present in all molluscs (used for
locomotion)
- Creeping movements
- Slime trail
- Digging
- Attachment
- Byssal threads
- For some, modified into proboscis
19. General Characteristics
Body in two parts
- Head-foot
- Foot is present in all molluscs (used for
locomotion)
- Creeping movements
- Slime trail
- Digging
- Attachment
- Byssal threads
- For some, modified into proboscis
20. General Characteristics
Body in two parts
- Visceral mass - contains digestive, respiratory, and reproductive organs
- Depends primarily on ciliary tracts for functioning
- Mantle - body wall of molluscs.
- Made of epidermis
- May have sense organs and glands
- Glands secrete mucus, cement, and shell (some)
- Mantle may create mantel cavity
- Cavity houses respiratory organs
- For some, mantle cavity may offer protection
24. General Characteristics
Body in two parts
- Visceral mass - contains digestive, respiratory, and reproductive organs
- Shell - secreted by mantle
- Much variability in form and structure
- Made of calcium carbonate
- 3 layers
- Periostracum
- Outer, thick in freshwater; thin or absent in marine
- Prismatic
- Middle, very dense
- Nacreous
- Inner, glossy and secreted throughout life
26. Homeostatic Structures and Functions
Respiration
- Most molluscs have folded, ciliated gills (ctenidia)
- Used for feeding in bivalves
- Bivalves may have extended siphon
- Some molluscs respire through skin
- Many terrestrial snail lack gills (pulmonates)
- Mantle is modified into saclike lung for breathing air
- Pneumostome present
30. Homeostatic Structures and Functions
Circulation
- Most have an open circulatory system
- Blood is not entirely contained within vessels
- Adequate for slow moving animals
- Cephalopods have closed circulation
- Heart is simple and has few vessels
- 2 auricles and 1 ventricle
- Coelom is reduced and becomes haemocoel surrounding heart
- Blood has both oxygen carrying cells and white blood cells
- No thrombocytes
- Haemocyanin (Cu) - most, blue in color
- Hemoglobin (Fe) - fewer, red in color
33. Homeostatic Structures and Functions
Feeding and Digestion
- Detritus feeders, burrowers, borers, grazers, carnivores, filter feeders, etc.
- Radula aids in feeding
- Most digestive organs are embedded in visceral mass
- Complete digestive system
- Foregut
- Midgut
- Hindgut
34. Homeostatic Structures and Functions
Feeding and Digestion
- Foregut - receives and prepares food
- Buccal cavity
- Mouth
- Radula
- Salivary glands
- Esophagus
35. Homeostatic Structures and Functions
Feeding and Digestion
- Midgut - storing region, crushing region
- Stomach
- Digestive glands
- Crystalline style
- Grinds food in some
37. Homeostatic Structures and Functions
Feeding and Digestion
- Hindgut - absorption of nutrients, formation of feces
- Intestine
38. Homeostatic Structures and Functions
Excretion
- 1 pair of metanephridia
- Term kidney is used, but different from vertebrate kidney)
- Some excretion through body walls and gills
39. Nervous System
Central nervous system - ring of ganglia
in head area
- Paired ganglia extend to other
parts of the body
- Nervous system is simple
compared to vertebrates
- Cephalopods rival some
mammals in reasoning and
learning
40. Reproduction and development
Most are dioecious
- Many gastropods (snails and slugs) are monoecious
Marine formes produce larval stage known as trochophore
- For some, a secondary larval form (veliger) will form
Cephalopods have direct development
41. Class Polyplacophora
Where found
- Generally on rocky surfaces in
intertidal regions
- Move very little over lifetime
- Clings to rocks with broad foot
- Capable of rolling up like armadillo
or pangolin for protection
- At low tide, can press margin of
mantle against substrate
- Lessens water loss
42. Class Polyplacophora
General morphology
- Small, 2-5 cm
- Dorsoventrally flattened
- Convex dorsal surface
- 7 to 8 plates on dorsal side (mantle
may cover)
- Generally dull in color
- Head reduced
- Mantle cavity extended along sides
of foot
45. Class Gastropoda
General characters
- Largest and most diverse class of
molluscs
- Variety of body forms and names
- Snails, limpets, slugs, whelks, conchs,
periwinkles, sea slugs, sea hares, sea
butterflies.
- Generally slow moving or
sedentary with heavy shells
46. Class Gastropoda
General characters
- Shells
- Always univalve (single piece)
- May be coiled or uncoiled
- Top is apex and contains the oldest and
smallest whorl
- Whorls become larger as they spiral
down the columella (central axis)
- Open is aperture and may be covered
by an operculum
47. Class Gastropoda
General characters
- Shells
- Always univalve (single piece)
- May be coiled or uncoiled
- Top is apex and contains the oldest and
smallest whorl
- Whorls become larger as they spiral
down the columella (central axis)
- Open is aperture and may be covered
by an operculum
49. Class Gastropoda
Torsion
- Process whereby the anus, shell, and mantle cavity containing the gills moves
from the posterior to anterior
- Occurs during development, but may not remain into adulthood (detorsion)
50. Class Gastropoda
Torsion
- Consequences
- Torsion prevents growth in length; gastropod must grow upward into shell
- Anus now over mouth
- Fouling
- What favored torsion?
- Most likely the advantage of withdrawing the head into the mantle cavity
- Provides protection
51. Class Gastropoda
Coiling
- Ancestral gastropods has a
planispiral (planospiral) shell
- All whorles stacked on top of one
another.
- Bulky arrangement; snail became much
taller as it grew
- Solution was coiling
52. Class Gastropoda
Feeding habits
- Varied, but all utilize the radula in
some fashion
- Herbivores - algae scrapers, grazers,
browsers
53. Class Gastropoda
Feeding habits
- Varied, but all utilize the radula in
some fashion
- Herbivores - algae scrapers, grazers,
browsers
- Borers - bore into other mollusc shells
54. Class Gastropoda
Feeding habits
- Varied, but all utilize the radula in
some fashion
- Herbivores - algae scrapers, grazers,
browsers
- Borers - bore into other mollusc shells
- Predators - use radula to help capture
food
55. Class Gastropoda
Feeding habits
- Varied, but all utilize the radula in
some fashion
- Herbivores - algae scrapers, grazers,
browsers
- Borers - bore into other mollusc shells
- Predators - use radula to help capture
food
- Conus - conotoxin
56. Class Gastropoda
Internal form and function
- Respiration
- Mostly by ctenidium (two gills) located
inside mantle cavity
- Pulmonates lack gills, but have highly
vascularized region
- Pneumostome
57. Class Gastropoda
Internal form and function
- Excretion - single nephridium (kidney)
- Circulatory - open
- Nervous - well developed
- Three pairs of ganglia
- Photoreceptors, statocysts, tactile organs, chemoreceptors
58. Class Gastropoda
Major groups of gastropods
- Prosobranchs - marine snails and some freshwater and terrestrial groups
- Opisthobranchs - sea slugs, sea hares, sea butterflies, bubble shells
- Nearly all marine
- Pulmonates - land snails and freshwater snails
- Ctenidia lost
59. Class Bivalvia
General characters
- Most will feed by creating ciliary
currents that draw water and
suspended food particles over gills
(filter feeding)
- Lack head, radula, and
cephalization (concentration of
sensory structures)
60. Class Bivalvia
General characters
- Shells always in two parts
- Hinge ligament at dorsal side
- Drawn together by adductor muscles
- Umbo is oldest part of shell
61. Class Bivalvia
Body and Mantle
- Visceral mass suspended from dorsal midline
- Muscular foot attached to visceral mass
- Ctenidia (gills) hang on either side of visceral mass and foot
- Mantle covers gills
- Gills lie in mantle cavity
- Shell to mantle to gill to visceral mass to gill to mantle to shell
- Mantle may be extended into long siphons
- Always forms some siphon (excurrent and incurrent)
62. Class Bivalvia
Locomotion
- Most initiate movement by
extending the foot through the gap
of the valves
- Blood is then pumped into the foot
causing it to swell
- Acts as anchor
- Longitudinal muscles shorten the foot
and pull the animal forward.
63. Class Bivalvia
Locomotion
- Most initiate movement by
extending the foot through the gap
of the valves
- Scallops move by jet propulsion
- Rapidly open and close valves to create
a jet of water
64. Class Bivalvia
Gills
- Gas exchange occurs over both
gills and mantle
- Gills appear as elongated “Ws”
- Form lamellae
- Water drawn in through incurrent
siphon
- Passes through pores into tubes and
then to suprabranchial chamber and out
excurrent siphon
65. Class Bivalvia
Gills
- Gas exchange occurs over both
gills and mantle
- Gills appear as elongated “Ws”
- Form lamellae
- Water drawn in through incurrent
siphon
- Passes through pores into tubes and
then to suprabranchial chamber and out
excurrent siphon
66. Class Bivalvia
Feeding
- Most are filter feeders
- As water is drawn in, mucus is secreted
- Entangles food particles
- Mucus and food slide down gillsto food groove at base of gills
- Mucus and food travel along the groove towards labial palps
- Palps direct food into mouth
68. Class Bivalvia
Feeding
- Floor of stomach is folded into ciliary tracts for sorting food particles
- In most, a styl sace secretes the crystalline style
- Constantly rotting
- Dissolves its surface layer and rolls the mucus mass
- Dislodged food particles are sorted by the base of the stomach
- Large particles to intestine
- Small to digestive gland
70. Class Bivalvia
Circulation
- Three-chambered heart with open circulation
Excretion
- Pair of U-shaped kidneys (nephridial tubes)
- Empty into suprabranchial chamber
Nervous system
- Three pairs of ganglia; poorly developed sense organs
- Scallops have eyes
71. Class Bivalvia
Reproduction
- Sexes usually separate
- For many, fertilization is external and gametes are shed into water
- Freshwater forms have internal fertilizations
- Many produce glochidia larvae
- Live parasitically on gills of fish
- Some discharge glochidia into water
- Others attract fish and cast glochidia directly at fish gills
74. Class Cephalopoda
General characters
- Foot is merged with head
- Forms funnel for expelling water and a crown of tentacles
- May be small (2-3 cm) or large (19 m)
- Ancestrally, shell was present and straight
- Derived forms have curved, coiled, reduced, or absent shell
- Found at great depths and shallow intertidal zones
75. Class Cephalopoda
Shell
- Coiled in Nautiloids and extinct
ammonoids
- Although heavy, made buoyant by gas-
filled chambers
- Chambers walled-off from one another
and only last is inhabited
- Cord of living tissue, siphuncle,
connects through all chambers
77. Class Cephalopoda
Locomotion
- Squids and cuttlefish are excellent, fast swimmers
- Nautiloids are much slower
- Octopuses are capable of rapid, backward movement, but are better built for
crawling among rocks
78. Class Cephalopoda
Respiration
- All cephalopods (except nautiloids) have one set of gills
- Gills lack cilia
- Rather, water is drawn over by changes to the shape of the mantle cavity
Circulation
- Circulatory system is closed
- Systemic heart served body
- Branchial hearts increase blood pressure at gills
79. Class Cephalopoda
Nervous system
- More elaborate than other molluscs
- Largest brain of any invertebrate
- Senses are well developed
- Eyes are single-lens, large, and complex
- No color vision; but superb underwater resolution
80. Class Cephalopoda
Communication
- Through chromatophores
- Cells will pigments
- Cell shape can be changed, thus the
amount of pigment shown can also be
changed
- Allows for rapid change in
appearance
81. Class Cephalopoda
Reproduction
- Sexes are separate
- Spermatozoa encased in
spermatophores
- Males with specializes tentacles to
retrieve spermatophore and pass it to
female
- Development is direct
