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Heterobranchia

Heterobranchia is a major clade of the class Gastropoda, comprising a highly diverse group of molluscs that includes many sea slugs, land snails, and related forms.

In traditional schemes it united Opisthobranchia and Pulmonata; modern phylogenetics treat Heterobranchia as a large clade

Characteristic features include detorted visceral mass in many lineages (a secondary reversal of the torsion seen

Habitat and diversity: Heterobranchs inhabit marine, freshwater, and terrestrial environments worldwide, from deep seas to mountains.

Taxonomic note and importance: Heterobranchia is a key lineage in molluscan evolution, illustrating major shifts in

within
Gastropoda,
with
Euthyneura
as
the
largest
subdivision.
The
composition
is
continually
revised;
some
groups
once
placed
in
Opisthobranchia
are
now
recognized
as
separate
subclades
within
Heterobranchia.
in
other
gastropods),
diversification
of
gill
and
mantle
structures,
and
often
loss
or
reduction
of
the
external
shell;
pulmonates
have
evolved
a
simple
terrestrial
lung
instead
of
a
gill.
They
include
sea
slugs
like
nudibranchs
and
bubble
snails,
as
well
as
land
snails
and
slugs.
They
show
a
wide
range
of
life
histories
and
adaptations,
including
carnivory,
herbivory,
and
detritivory.
morphology
and
ecology
within
gastropods.
Their
study
informs
understanding
of
torsion,
shell
reduction,
and
the
evolution
of
lungs
in
molluscs.