Download The Lophotrochozoa are protostomes possessing a

The Lophotrochozoa are protostomes possessing a blastopore, an
early form of a mouth; they include the trochozoans and the
lophophorata.
LEARNING OBJECTIVE [ edit ]
Describe the phylogenetic position and basic features of lophotrochozoa KEY POINTS [ edit ]
Lophotrochozoa have a blastopore, which is an involution of the ectoderm that forms a
rudimentary mouth opening to thealimentary canal, a condition called protostomy or "first
mouth".
The Lophotrochozoa are comprised of the trochozoans and the lophophorata, although the exact
relationships between the different phyla are not clearly determined.
Lophophores are characterized by the presence of the lophophore, a set of ciliated tentacles
surrounding the mouth; they include the flatworms and several other phyla whose relationships
are upheld by genetic evidence.
Trochophore larvae are distinguished from the lophophores by two bands of cilia around the
body; they include the Nemertea, Mollusca, Sipuncula, and Annelida.
The lophotrochozoans have a mesoderm layer positioned between the ectoderm
and endoderm and are bilaterally symmetrical, which signals the beginning of cephalization, the
concentration of nervous tissues and sensory organs in the head of the organism.
TERMS [ edit ]
cephalization
an evolutionary trend in which the neural and sense organs become centralized at one end (the
head) of an animal
blastopore
the opening into the archenteron
lophophore
a feeding organ of brachiopods, bryozoans, and phoronids
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Lophotrochozoans
Animals belonging to superphylum
Lophotrochozoa areprotostomes: the
blastopore (or the point of involution of
the ectoderm or outer germ layer)
becomes the mouth opening to the
alimentary canal. This is called
protostomy or "first mouth." In
protostomy, solid groups of cells split
from the endoderm or inner germ layer to
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form a central mesodermal layer of cells. This layer multiplies into a band which then splits
internally to form the coelom; this protostomic coelom is termed schizocoelom.
As lophotrochozoans, the organisms in this superphylum possess either lophophore or
trochophore larvae. The exact relationships between the different phyla are not entirely
certain. The lophophores include groups that are united by the presence of the lophophore, a
set of ciliated tentacles surrounding the mouth. Lophophorata include the flatworms and
several other phyla, including the Bryozoa, Entoprocta, Phoronida, and Brachiopoda.
These clades are upheld when RNA sequences are compared. Trochophore larvae are
characterized by two bands of cilia around the body. Previously, these were treated together
as the Trochozoa, together with the arthropods, which do not produce trochophore larvae,
but were considered close relatives of the annelids because they are both segmented.
However, they show a number of important differences. Arthropods are now placed
separately among the Ecdysozoa. The Trochozoa include the Nemertea, Mollusca, Sipuncula,
and Annelida.
The lophotrochozoans are triploblastic, possessing an embryonic mesoderm sandwiched
between the ectoderm and endoderm found in the diploblastic cnidarians. These phyla are
also bilaterally symmetrical: a longitudinal section will divide them into right and left sides
that are symmetrical . They also show the beginning of cephalization: the evolutionof a
concentration of nervous tissues and sensory organs in the head of the organism, which is
where it first encounters its environment.
Lophotrochozoans
The Caribbean Reef Squid or Sepioteuthis sepioidea is a complex lophotrochozoan. Species in this group
have bilateral symmetry.