Download seun_s_GEY_205_assignment_1

Name: Opoola Oluwaseun.
Course: GEY 205.
Matric no: D/E.
Dep: Geology.
1) Geologic distribution of gastropods:
any member of more than 65,000 animal species
belonging to the class Gastropoda, the largest group in
the phylum Mollusca. The class is made up of the
snails , which have a shell into which the animal can
generally withdraw, and the slugs —snails whose shells
have been reduced to an internal fragment or
completely lost in the course of evolution.
Gastropods are among the few groups of animals to
have become successful in all three major habitats: the
ocean, fresh waters, and land. A few gastropod types
(such as conch , abalone , limpets, and whelks) are used
as food, and several different species may be used in
the preparation of escargot. Very few gastropod species
transmit animal diseases; however, the flukes that
cause human schistosomiasis use gastropods as
intermediate hosts. The shells of some species are used
as ornaments or in making jewelry. Some gastropods
are scavengers, feeding on dead plant or animal matter;
others are predators; some are herbivores, feeding on
algae or plant material; and a few species are external
or internal parasites of other invertebrates.
The Gastropoda or gastropods, more commonly known
as snails and slugs , are a large taxonomic class within
the phylum Mollusca . The class Gastropoda includes
snails and slugs of all kinds and all sizes from
microscopic to large. There are many thousands of
species of sea snails and sea slugs , as well as freshwater
snails , freshwater limpets , land snails and land slugs .
The class Gastropoda contains a vast total of named
species, second only to the insects in overall number. The
fossil history of this class goes back to the Late
Cambrian. There are 611 families of gastropods known,
of which 202 are extinct and appear only in the fossil
record. [3]
Gastropoda (previously known as univalves and
sometimes spelled "Gasteropoda") are a major part of the
phylum Mollusca, and are the most highly diversified
class in the phylum , with 60,000 to 80,000 [3][4] living
snail and slug species . The anatomy , behavior, feeding,
and reproductive adaptations of gastropods vary
significantly from one clade or group to another.
Therefore, it is difficult to state many generalities for all
gastropods.
The class Gastropoda has an extraordinary
diversification of habitats . Representatives live in
gardens, woodland, deserts, and on mountains; in small
ditches, great rivers and lakes; in estuaries , mudflats , the
rocky intertidal , the sandy subtidal, in the abyssal depths
of the oceans including the hydrothermal vents , and
numerous other ecological niches, including parasitic
ones.
Although the name "snail" can be, and often is, applied to
all the members of this class, commonly this word
means only those species with an external shell large
enough that the soft parts can withdraw completely into
it. Those gastropods without a shell, and those with only
a very reduced or internal shell, are usually known as
slugs.
The marine shelled species of gastropod include edible
species such as abalone , conches, periwinkles, whelks ,
and numerous other sea snails that produce seashells
that are coiled in the adult stage—though in some, the
coiling may not be very visible, for example in cowries . In
a number of families of species, such as all the various
limpets , the shell is coiled only in the larval stage, and is
a simple conical structure after .
Fossil assemblages of different geographical regions and
within certain latitudes which are equivalent on the genus or
family level indicate temperature-controlled realms in the
geologic past. Paleobiogeographically, the Tethys is placed
within the Tropical realm of the Mesozoic. In addition to the
low-latitude Tropical realm. Warm Temperate. Temperate,
and probably also Subpolar marine provinces can be
distinguished by the distribution of fossils in Cretaceous
rocks. In low latitudes, the horizontal distribution is to a
varying degree vertically reproduced.
Like all benthic organisms the gastropods are restricted to
specific environments. This distribution pattern is discussed
for the nerineaceans (including the itieriids), the
actaeonellids (Actaeonella and Trochactaeon ), the cassiopids
and the genera Trajanella and Discotectus . Valid
biostratigraphic analyses can be obtained only by
comparing stratigraphic ranges within the same
environments.
Normally, marine gastropod assemblages of rocky surfaces
or patches of hard substrates show high diversities of
archaeogastropods. Level bottom communities are
characterized by a high diversity of mesogastropods and
cephalaspidean opisthobranchs. The evolution of
neogastropods allows this group to become increasingly
dominant during the Creataceous; the number of
nerineacean genera is in the process of decreasing after the
Cenomanian.
The origin of the neogastropods was within the Temperate
marine zone. In the Tethyan realm, neogastropods were not
recorded prior to the Upper Albian. It is assumed, that the
first neogastropods were buccinids which have evolved
from deposit-feeding groups.
The Tethyan gastropods were profoundly affected by the
terminal Cretaceous events. The extinction of Tethyan
gastropods is interpreted as having been primarily caused
by a change of surface water temperature distribution in the
marine biosphere.
2) A typical member of pelecypods:
E.g:Clams, Oysters, Mussels, Scallops;
-They are bilaterally symmetrical.
-They are bivalve.
-Their shell composition is usually calcareous.
-The two shells are equal.
-There is right and left valve.
-Plane of symmetry is between the two valves.
-Teeth and socket on each valve.
-They show wide range of variation.
-They are laterally compressed and has a prominent ventral foot.
-Members are usually free moving bottom dwellers where they are usually attached to the
sub-stratum.