Class

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Class Gastropoda (stomach- Foot)
Highly diverse Group and only Mollusc to come
out (of the Water)
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Ancestral mollusc Is closest to The
primitive gastropod
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Summary diagram of diversity Of forms of
gastropods-crawling in water And on land,
swimming-with/without shell
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Land gastropods-with Without shell-every Gardner
s favorite-the slug
The Limpet- A tide Pool favorite
Naked gastropod-the Nudibranch-every tide
pool Hunters prize
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Gastropods have Some specialized Appendages The
radula is one Of those that these Organisms
require To grind their food Off of hard surfaces
ANOTHER is the Operculum which acts As a hatch
cover to Isolate the animal from The elements
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Soft parts include most Of the same organs
except As the name implies, these Have their
stomach literally In their foot One defining
feature is torsion Of the gills as animal
develops 1a is gills at posterior-only Extinct
group had this form-all Others end up through
develop- ment with gills anterior Note position
of OPERCULUM Which covers aperture
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Types of coiling 1-planispiral 2-pseuodplanispiral
3-conispiral(also Called trochospiral) 4-conispir
al Limpets have spiral- Just an open
simple shell
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Some morphological terms
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Different types of coiling
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Class Gastropoda Cam.-Rec. Stomach foot
translated, with or without shells of CaCO3 ,
occupy almost every aquatic niche Subclass
Amphigastropoda Cam.- Perm. (Triassic?)
Gills posterior (no modern reps of this
group), shells Symmetrical Subclass
Prosobranchia Cam.-Rec. Gills anterior,
cap-shaped or conispiral shells Order
Archaegastropoda Cam.-Rec. Primitive 2
subequal gills Order Mesogastropoda
Penn.-Rec. Only 1 gill Order
Neogastropoda Cret.-Rec. Gill
structure like Meso- group but with well
Developed siphon
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Subclass Opistobranchia Miss.-Rec. Gills
commonly absent but when Present
twisted into posterior position, often no shell
Order Pleurocoela Miss.-Rec.
Has gills and shell Order Pteropoda
Cret. Rec. winged shell modified
for swimming, gills Order Sacoglossa
Recent No shell, no gills, no
fossils known, slugs Subclass Pulmonata Penn.
Rec. Mostly shell bearing but lacking
operculum, mantle cavity modified as a
primitive lung Order Basommatophora
Jur.-Rec. Freshwater with eyes at
base of tentacles Order Stylommatophora
Penn.-Rec. Terrestrial pulmonates
having eyes at the tip of their tentacles
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Earliest Gastropods- Mostly Amphi- Gastropods
and archaeogastropods
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Comparison of gill types 1)Amphigastropod
gills 2) Amphigastropod 3) Bellerophon 4)Prosobra
nch 5)planispiral cepholopod
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These are placed in the subclass
Amphi- Gastropoda but since there are no
living Representatives it is difficult to know
for sure
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Ordovician Gastropods Archaeogastropods- 1-9,11,12
,14-16 Bellerophontacea- 10,13
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More Ordovician Gastropods All Archaeogastropods (
1,2,4-7,9-12) except 3 and 8 which
are Bellerophontids
Mid-Ord. Hyperstrophic Archaeogast. Note
operculum
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Silurian gastropods All archaeogastropods Except
9 which is a bellerophontid
S.F. Pleurotomariacea Cam.-Rec
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Devonian Gastropods All archaeogastropods Except
6 and 7(bellerph.)
Time distribution of S.F. Euomphalacea
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Pennsylvanian
Mississippian
Representative Gastropods of the
Carboniferous
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Representative Pennsylvanian and Permian
gastropods
Fig. 2 is the oldest Member of the Subclass
Pulmonata, The first land snail 3,4, 7 and 8 are
bellerophontids
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Representative Jurassic Gastropods-all
Archaeogast. Except 7-9 which are Mesogastropods
Some Representative Archaeogastr.
S.F. Loxonematacea
S.F. Neritacea
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Lower Cretaceous Gastropods Archaeogastr.(3,9,11)
Opistobranchs(5,13) Mesogastropods comprise the
remainder
Distribution of S.F.Cerithiacea Figures 4,6,8
above
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Upper Cretaceous Gastropods-all Proso- Branchs
except 15(opisthobranch)
Mesogastro(2,8,13) Neogastro(1,3-7,9-12, 14,16)
Mesogastro. Distribution S.F.s Strombacea And Nat
icacea
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Upper Cretaceous gastropods Opisthobranchs(4) Meso
gastro(3) Rest are Neogastropods
Geologic distribution Of some mesogastropoda super
families
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Paleogene gastropods Archaeogastro-14 Mesogastros
-2,4-7,11, 15,17 Neogastgros-1,8,12,16 Opisthobra
nchs- 9,10 Scaphopod-3
Mesogastro. S.F. Rissoacea
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Paleocene distribution Of Gastropods Archaeogastro
-2,13 Mesogastro-6,11,14-16 Remainder are Neogast.
Mesogastro 3 SFs distribution
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Representative Neogene gastropods-includes all
groups of Gastropods except Amphigastropods
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A group of incertae setis In your book these
are put with Pteropods(doubtfully) but we Now
know those dont show up Until the Cretaceous
Typical living forms Of neogastropods
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GASTROPOD TRENDS IN MORPHOLOGY 1)Increased
tightness of whorl (coiling)-evolute to
involute 2)Accentuation of orthostrophy
(downward) or hyperstrophy (upward). Increased
shell elevation 3)Diminution of same (flatter
cones) 4)Progressive modification of whorl
leading to or away from special forms 5)Increase
or decrease of upper whorl angulation-ridges,
shoulders 6)Flattening or rounding of anterior
projection of shell base 7)Elongation/shortening
of canal 8)Development of thickness in areas like
the callus 9)Modification of aperture 10)Increase
or decrease of prominence of shell
ornamentation 11)Development of spirally arranged
indentations on inside of whorls 12) Infilling
of apical region or blocking of some whorls by
septa 13) Reduction of shell size 14) Loss of
operculum as in Pulmonates
The basic point is that there is no
basic Morphological trends
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Geologic Ranges Subclass Amphigastropoda

Cam-Perm., Tria?
Subclass Prosobranchia Cam-Rec. order
ARCHaeogastropoda Cam-Rec order
MESOgastropoda Penn.-Rec. order
NEOgastropoda Cret. -Rec.
Subclass
Opisthobranchia Miss-Rec.
Subclass Pulmonata Penn. -Rec.
Only class of molluscs that occupies all
niches(except the air) First group of
invertebrates we study that starts to show
Preference for no shell(i.e. mobility over
armor) in Opisthobranchs