Polyzoa and Kryptozoa

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Polyzoa and Kryptozoa

• Chapter 15

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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  withdrawn for protection.

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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.

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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.

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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
  U-shaped gut ending with an anus that opens
  outside the ciliated ring.
• Acoelomate body
• Life cycle has sexual and asexual phases

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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.

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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.

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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.

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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.

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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
  trochophore-like larva.

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Phylum Ectoprocta

• Phylum Ectoprocta contains aquatic animals that
  often encrust hard surfaces (bryozoans).
• Approximately 4500 living species.
• Inhabit both shallow freshwater and marine
  habitats.

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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.

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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.

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Phylum Ectoprocta

• Zooids feed by extending lophophores into
  surrounding water to collect tiny particles
• Zooids secrete exoskeleton in which they live in.

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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.

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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.

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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.

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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.

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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.

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Phylum Ectoprocta

• Freshwater ectoprocts undergo budding that
  produces statoblasts.
• Hard, resistant capsules containing a mass of
  germinative cells.

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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.

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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).

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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.

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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.

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Phylum Phoronida

• Characteristics of both protostomes
  deuterostomes
• Blastopore becomes mouth (protostome).
• Cleavage is radial (deuterostome).
• Coelom formation highly modified enterocoelous
  (deuterostome).

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Phylum Nemertea

• Ribbon worms, phylum Nemertea, use a proboscis to
  capture prey.
• Almost completely marine.
• Active predators.
• General body plan similar to turbellarians.

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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.

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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.

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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.