Smaller Protostome Phyla

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Smaller Protostome Phyla

• Chapter 21

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Small Coelomate Phyla

• Several small phyla of protostome coelomates
  include examples from superphyla Lophotrochozoa
  and Ecdysozoa
• Lophotrochozoans
• Phylum Sipuncula
• Phylum Echiura
• Phylum Pogonophora
• Phylum Ectoprocta
• Phylum Brachiopoda
• Phylum Phoronida

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Small Coelomate Phyla

• Sipuncula, Echiura, Pogonophora are similar in
  many ways to annelids and molecular evidence
  suggests that perhaps they should be included
  within phylum Annelida.

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Phylum Sipuncula

• Phylum Sipuncula consists of marine, benthic
  worms that often live burrowed in the sand.
• Retractable proboscis used for feeding.
• Deposit or suspension feeders.
• Trochophore larva

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Phylum Echiura

• Phylum Echiura is another group of marine,
  benthic worms that often live in the sediment.
• Extend proboscis (cant be retracted) out to
  pick up particles of detritus.
• Trochophore larva

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Phylum Pogonophora

• Phylum Pogonophora includes the tube-dwelling
  vestimentiferan worms found at hydrothermal vent
  systems.
• No digestive tract most nutrition comes from
  symbiotic chemoautotrophic bacteria that use
  hydrogen sulfide to produce energy.

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Lophophorates

• Phoronida, Ectoprocta, Brachiopoda are
  seemingly different phyla that have several
  characteristics in common.
• Coelomate
• Protostome and deuterostome characteristics
• No distinct head
• Lophophore a unique arrangement of ciliated
  tentacles on a ridge surrounding the mouth, but
  not the anus.

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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 Ectoprocta (Bryozoa)

• Bryozoans (phylum Ectoprocta) are aquatic, mostly
  shallow water.
• Mostly colonial.
• Fossils date to the Ordovician (505 mya).
• Complete digestive system.
• Mostly hermaphroditic.

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Phylum Ectoprocta (Bryozoa)

• Characteristics of both protostomes
  deuterostomes
• Cleavage is radial (deuterostome) but determinate
  (protostome).

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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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Small Ecdysozoan Phyla

• Some of the phyla within the Ecdysozoa are very
  closely related to the arthropods.
• Phylum Onychophora
• Phylum Tardigrada
• Phylum Chaetognatha

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Phylum Onychophora

• Velvet worms (phylum Onychophora) are nocturnal
  caterpillar-like animals that have changed little
  over 500 million years.

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Phylum Tardigrada

• Tardigrades, or water bears, are less than a
  millimeter in length.
• Freshwater or marine
• Live in spaces between sand grains.
• Tardigrade clips

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Phylum Tardigrada

• They share many characteristics with arthropods.
• But legs are unjointed.
• Non-chitinous cuticle that is molted.

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Phylum Tardigrada

• Tardigrades can enter a state called
  cryptobiosis, where metabolism is imperceptible.
• In this state, they can withstand harsh
  conditions
• Extreme low temps
• Desiccation

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Phylum Chaetognatha

• The arrow worms, phylum Chaetognatha, are all
  marine, planktonic organisms.
• Some deuterostome embryological characters.
• Molecular works suggests they are protostomes.

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Phylogeny

• Sipunculans, echiurans and annelids are probably
  very closely related.
• Placement of phorids, brachiopods, and ectoprocts
  is difficult due to the mixture of protostome and
  deuterostome characteristics.