Transcript Pseudocoelomate Animals

Polyzoa and Kryptozoa
Chapter 15
Lophophores
• Phylogenetic evidence indicates that
lophophores evolved more than once.
• Lophophores have a crown of ciliated tentacles that
are used in food capture and respiration.
• Cavity inside the lophophore is part of the coelom
and filled with coelomic fluid.
• Thin ciliated walls act as respiratory surface for gas
exchange.
• Lophophores normally extended but can be
withdrawn for protection.
Lophophores
 Three major phyla were previously lumped
under lophophores: Phoronida, Ectoprocta,
Brachiopoda.
 Lophophores and animals with trochophore larvae
features are merged to form a new group called
Lophotrochozoans.
 Ectoprocta is now placed in a clade called Polyzoa
with Cycliophora and Entoprocta where all three taxa
share ciliated tentacles.
 Brachipoda and Phoronida are placed in the clade
Brachiozoa.
Phylum Cycliophora
• Phylogenetic studies using multiple genes have
supported the clade Polyzoa that unites the
cycliophorans, entoprocts and ectoprocts.
• Members of the three groups have fascinating body
plans and life cycles.
• Cycliophorans live exclusively on mouthparts of
marine decapod crustaceans in northern
hemisphere.
• Attach to bristles with an adhesive disc on the end of
an acellular stalk.
Phylum Cycliophora
 Feed by collecting bacteria or bits of food dropped
from their lobster host on a ring of compound cilia
that surrounds the mouth.
 Simple body plan where the mouth leads to Ushaped gut ending with an anus that opens outside
the ciliated ring.
 Acoelomate body
 Life cycle has sexual and asexual phases
Phylum Entoprocta
 About 150 species in
the phylum
Entoprocta occur
worldwide.
 Usually in marine
environments.
 Less than 5 mm long
and mostly
microscopic,
resembling hydroid
cnidarians.
Phylum Entoprocta
 Urnatella gracilis is a common freshwater species in
North America.
 Body or calyx is cup shaped and bears a circular crown
of ciliated tentacles.
 Attaches by a stalk with adhesive glands.
Phylum Entoprocta
 Tentacles (3-30) and stalk are continuations of the body
wall.
 Tentacles on lateral and inner surfaces can roll inward
but cannot be retracted into the calyx.
 Gut is U-shaped with both mouth and anus opening
within the circle of tentacles.
Phylum Entoprocta
 Long cilia on sides generate current bringing in
particles.
 Short cilia on inner surfaces capture food and
direct it to mouth.
 Pair of protonephridia embedded in gelatinous
parenchyma.
 Well-developed nerve ganglion on the ventral side
of stomach.
 No circulatory or respiratory organs.
Phylum Entoprocta
 Some are monoecious, some dioecious, and
some first produce sperm and later eggs.
 Fertilized eggs develop in a brood pouch.
 Modified spiral cleavage leads to trochophorelike larva.
Phylum Ectoprocta
 Phylum Ectoprocta
contains aquatic
animals that often
encrust hard
surfaces
(bryozoans).
 Approximately 4500
living species.
 Inhabit both shallow
freshwater and
marine habitats.
Phylum Ectoprocta
 Most are sessile, some slide slowly, and others crawl
actively across surfaces.
 Mostly colony builders.
 Each member is less than 0.5 mm in length and is
called a zooid.
Phylum Ectoprocta
 Ciliated tentacles are also a respiratory device
permitting gas exchange between surrounding water
and internal coelomic fluid.
 Gut is U-shaped:
 Mouth opens inside the lophophore ring, and the anus
opens outside the ring.
Phylum Ectoprocta
 Zooids feed by
extending
lophophores into
surrounding water to
collect tiny particles
 Zooids secrete
exoskeleton in which
they live in.
Phylum Ectoprocta
 Exoskeleton may be gelatinous, chitinous, or stiffened




with calcium and possibly impregnated with sand.
Shape may be boxlike, vaselike, oval, or tubular.
Some colonies form limy encrustations on seaweed,
shells, and rocks.
Others form fuzzy or shrubby growths or erect branching
colonies.
Freshwater colonies may form mosslike colonies on
stems of plants or on rocks.
Phylum Ectoprocta
 To feed, the lophophore
is extended and
tentacles spread out
into a funnel.
 Cilia on tentacles draw
water into funnel.
 Food particles caught
by cilia in the funnel are
drawn into the mouth.
 Digestion begins
extracellularly in the
stomach and is
completed intracellularly
within the intestine.
Phylum Ectoprocta
 Respiratory, vascular, and excretory organs
absent.
 Gas exchange is through body surface.
 Ganglionic mass and a nerve ring around the
pharynx.
 No sense organs.
Phylum Ectoprocta
 Reproduction - most hermaphroditic.
 Some species shed eggs into seawater, but most
brood their eggs.
 Brooding occurs within coelom and some have an
external chamber called an ovicell.
 Sometimes embryos proliferate asexually from the
initial embryo.
 Cleavage is radial but mosaic.
Phylum Ectoprocta
 Larva of brooding species do not feed and settle after a
brief free-swimming existence.
 Attach to substratum by secretions from an adhesive
sac, then metamorphose to adult form.
 New colonies begin from this single metamorphosed
primary zooid, called an ancestrula.
 Ancestrula undergoes asexual budding to produce
many zooids of a colony.
Phylum Ectoprocta
 Freshwater
ectoprocts undergo
budding that
produces
statoblasts.
 Hard, resistant
capsules containing a
mass of germinative
cells.
Phylum Brachiopoda
 Brachiopods appear
similar to bivalve
molluscs because they
have two calcareous
shell valves secreted by
a mantle.
 Dorsal/ventral instead
of left/right.
 Pedicel – a fleshy stalk
used for attachment.
Phylum Brachiopoda
 Brachiopods are an
ancient group they
were prolific during the
Paleozoic and
Mesozoic eras.
 One living species,
Lingula, is considered
to be a living fossil
since it has changed
little since the
Ordovician (505 mya).
Phylum Brachiopoda
 Characteristics of both protostomes &
deuterostomes:
 Cleavage is radial (deuterostome)
 Coelom formation enterocoelous at least in some
brachiopods. (deuterostome)
 The relationship of the blastopore to the mouth is
uncertain.
Phylum Phoronida
 Species in the phylum
Phoronida are small
wormlike animals.
 Secrete tubes to live in.
 Tentacles of the
lophophore are
extended for feeding.
 U-shaped digestive
tract.
Phylum Phoronida
 Characteristics of both protostomes &
deuterostomes:
 Blastopore becomes mouth (protostome).
 Cleavage is radial (deuterostome).
 Coelom formation – highly modified enterocoelous
(deuterostome).
Phylum Nemertea
 Ribbon worms,
phylum Nemertea,
use a proboscis to
capture prey.
 Almost completely
marine.
 Active predators.
 General body plan
similar to
turbellarians.
Phylum Nemertea
 An anus is present providing these worms
with a complete digestive system.
 Nermeteans are the simplest animals to have
a closed loop blood-vascular system.
Phylogeny and Diversification
 Molecular characters have changed the phylogeny of
Lophophores and its associated groups.
 Developmental characters associated with spiral
cleavage are presumed to be ancestral to the clade.
 Spirally cleaving embryos have mosaic cleavage
patterns and mesoderm formation from particular
endoderm cells.
 But many members of the Lophophores do not follow
these features and prevent clear placement into
specific clades and groups.
Phylogeny and Diversification
 Placement of Nemerteans are contentious and highly
debatable.
 Nemerteans used to be with Platyhelminthes due to
flame cells and cilated epidermis but the presence of
complete digestive tract and reversible proboscis in a
unique coelomic cavity counters this original
grouping.
 Nemerteans coelomic cavity above the digestive
tract sets them apart form other coelomate animals.