2. WHAT ARE GASTROPODS?
Gastropods are snail-like and slug-like invertebrate (lacking a backbone)
animals, and are types of mollusks. Snails have hard mineral shells; slugs lack
shells. Because fossils mostly represent the hard parts of organisms,
Gastropods evolved early in the Cambrian, but since the Paleogene they have
become the most common molluscs, inhabiting both aquatic and terrestrial
environments.
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.
4. TYPES OF GASTROPODS
Three main gastropod groups are the prosobranchs (subclass
Prosobranchia), the opisthobranchs (subclass Opisthobranchia), and
the pulmonates (subclass Pulmonata)
prosobranchs: any of a
subclass (Prosobranchia)
of gastropod mollusks
that have the loop of
visceral nerves twisted
into a figure eight, the
sexes usually separate,
and usually an
operculum
Source:google
5. OPISTHOBRANCHS
Opisthobranchs are special in that
their gill is located behind the
heart, other than the
prosobranchs and pulmonate
snails, where the respective
respiratory organs still are
located in front of the heart
Source:google
6. PULMONATES
They have lost their ancestral gills and breathe
instead by means of a “lung”—a highly
vascularized saclike modification of the mantle
cavity. Some snails lack an external shell, but
most pulmonates have a spiral shell that may be
attenuated or flattened. They are anatomically
more advanced than other snails: all are
detorted (bilaterally symmetrical, with an
unlooped nerve cord) as adults, and the auricle
of the heart is anterior to the ventricle.
Source:google
7. The earliest undisputed gastropods date from the Late
Cambrian Period, around 500 million years ago
How do you identify a gastropod fossil?
Gastropods can be recognized by their large foot,
tentacles, coiled shell (although this is sometimes small
or absent) and the presence of torsion, which is where
the body is twisted round so that the anus, reproductive
organs, mantle cavity and gills all point forwards.
Source:google
8. PERMIAN-TRIASSIC MASS EXTINCTION
The end-Permian mass extinction had a major and lasting impact on
gastropods. In general, Paleozoic and post-Paleozoic gastropods differ
markedly, and this is in large part due to the extinction. For example,
Paleozoic gastropods mostly had two gills, were slow-moving
suspension-feeders or herbivores, and frequently had little external
shell ornamentation. Post-Paleozoic gastropods, in contrast, include
more active, mobile forms, as well as more carnivores; most have a
single gill, which allows for a more elongate aperture, the
development of an inhalant siphon, and a more streamlined shell
shape. In detail, however, the changes that accomplished this
transition were complex. Global diversity of gastropods began to
decline as much as 14 million years before the end of the Permian,
with about 45% of genera becoming extinct at the very end
