The other deuterostomes

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The other deuterostomes Chapter 23
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Phylum Chaetognatha

• arrow worms
• marine, planktonic, voracious predators
• well-developed nervous sensory systems
• no gas exchange systems, no excretory systems
• no well-developed circulatory system
• only longitudinal muscles
• complete gut
• hermaphroditic

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Chaetognaths

• spines on either side of head for capturing prey
• 2 dorsal eyes on head aid in visual predation
• tripartite coelom (protocoel, 2 mesocoels, 2
  metacoels) matches echinoderm larvae
• ciliary fans covering body sense vibrations in
  water (prey)
• hermaphroditic

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Phylum Hemichordata

• Wormlike, benthic marine organisms
• Live intertidally, in sediment or attached to
  hard substrate or holdfasts on bottom
• 3 coeloms (protocoel, 2 mesocoels, 2 metacoels)
  as in echinoderm larvae
• Chordate features dorsal nerve cord, gills slits
• No notochord
• Support from coeloms, hydrostatic skeleton
• 3 classes Enteropneusta (acorn worms)
• Pterobranchia (pterobranchs)
• Planctosphaeroidea (only 1 species)

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Phylum Hemichordata Class Enteropneusta

• Live in shallow water, burrow in sediment
• 3 body parts proboscis, collar, trunk
• Gill pores on anterior trunk, for gas exchange
• Direct deposit feeders
• Dioecious, free-spawners, deuterostomous
  development
• Chemical defenses in some

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Phylum Hemichordata Class Enteropneusta

• Locomotion in Balanoglossis by peristaltic
  action in the proboscis

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Phylum Hemichordata Class Enteropneusta

• Balanoglossis food selection rejection using
  proboscis cilia

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Phylum Hemichordata Class Pterobranchia

• Generally live in deep water, mostly colonial
• Considered to be the most primitive of the
  hemichordates
• Feeding with mucus net spread across zooids
• U-shaped gut with anteriodorsal anus
• Dioecious, but budding (asexual reproduction) is
  common

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Phylum Chordata

• most chordates are vertebrates
• chordate traits
• notochord
• dorsal hollow nerve cord
• pharyngeal gill slits
• muscular locomotory postanal tail at some point
  in life history
• complete gut with regional specialization
• circulatory system with ventral heart
• tadpole stage in life history of all taxa
• dioecious or hermaphroditic

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Phylum Chordata Subphylum Urochordata Class
Ascidiacea

• sea squirts or ascidians
• sessile marine tunicates, live attached to hard
  surfaces
• oral (buccal) and atrial siphons
• tadpole larva, with notochord, dorsal nerve cord
  in tail
• adults do not have notochord or nerve cord
• filter feed pump water through pharyngeal
  basket, catch particles on mucus produced by
  endostyle
• U-shaped digestive tract

Ascidian filter feeding animation
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Phylum Chordata Subphylum Urochordata Class
Ascidiacea
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Phylum Chordata Subphylum Urochordata Class
Thaliacea (salps)

• free-swimming, planktonic as adults
• oral and atrial siphons at opposite ends of the
  body
• water current for gas exchange, feeding,
  locomotion

• transparent, gelatinous
• many are colonial (form chains)

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Phylum Chordata Subphylum Urochordata Class
Appendicularia (Larvacea)

• marine, planktonic, small organisms
• adults have retained the larval characteristics
  of tunicates (paedomorphosis) tail with a
  notochord nerve cord
• no tunic they secrete a gelatinous house to
  enclose their body and filter feed
• house has incurrent excurrent siphons, plus
  mesh screens to keep out big particles
• beat tail to pump water through house exiting
  water propels animal through the water
• continually make new houses

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Phylum Chordata Subphylum Cephalochordata

• body plan intermediate between invertebrates and
  vertebrates
• dorsal hollow longitudinal nerve cord
• notochord is homologous with vertebrate notochord
• benthic, live burrowed in sand in shallow waters
• filter-feed particles out of the water use mucus
  to capture particles
• no cuticle, no tunic
• reduced coelom provides structural support
• dioecious, with external fertilization

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Chordate phylogeny