Pseudocoelomates

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Pseudocoelomates

• 2 groups of phyla
• Ecdysozoan
• Lophotrochozoan

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Ecdysozoan Phyla

• Nematoda
• Nematomorpha
• Kinorhyncha
• Loricifera
• Priapulida

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Lophotrochozoan Phyla

• Rotifera
• Acanthocephala
• Gastrotricha
• Entoprocta

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Phylum Rotifera

• Characteristics
• 1800 species worldwide
• Some colonial
• Coronaciliated crown, beats like rotating wheel
• Usually circular or a pair of trochal (wheel)
  discs

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Characteristics, cont.

• Floatersglobular
• Creeperselongated
• Sessile formsvase-like
• Cyclomorphosisbody form varies to adapt to
  seasonal or food changes

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Habitats/Niches

• Most freshwater
• Few marine
• Few terrestrial
• Few parasitic
• Encyst to endure dessication or extreme
  temperature changes

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Form and Function

• Head, trunk, tail
• Ciliated corona surrounds nonciliated area with
  sensory bristles and mouth
• Beating cilia aid in feeding, locomotion
• Adhesive foot with 1 to 4 toes may be retractile

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Form and Function, cont.

• Some with cuticle
• All have fibrous layer within epidermis
• Sometimes very thick, forming a lorica (case)
• Muscles under cuticle
• Large fluid-filled pseudocoel

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Feeding Mechanisms

• Coronal cilia sort out large, unsuitable
  particles
• Mastax
• Muscular pharynx with trophi (jaws)
• Trappers
• Funnel shaped area around mouth
• Hunters
• Huntersproject trophi to seize prey

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Philodina rotifer structure
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Digestion/Excretion

• Complete digestive system
• Mouth to anus
• Salivary gastric glands secrete enzymes
• Stomach absorbs nutrients
• Protonephridial tubules with flame cells empty to
  bladder then to cloaca

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Osmoregulation

• Protonephridia important in both freshwater and
  marine species
• Water enters through mouth bladder empties
  regularly

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Nervous System

• Bilobed brain
• Paired nerves leading to organs
• Sensory organs
• Eyespots
• Sensory bristles and papillae
• Ciliated pits
• Dorsal antennae

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Reproduction

• Dioecious
• Males smaller than females
• Males inject sperm into pseudocoel of female

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Class Monogononta reproduction
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Reproduction, cont.

• Class Bdelloidea
• Females parthenogenetic (males unknown)
• Class Monogononta
• Life cycle varies with environmental conditions
• Eggs mictic, amictic, dormant

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Nuclear Constancy

• Most structures are syncytial, but many species
  exhibit eutely
• One species reported
• always183 nuclei in brain
• Always 39 nuclei in stomach
• Always 172 nuclei in corona

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Phylum Acanthocephala

• Spiny-headed worms
• 500 species worldwide
• Intestinal parasites of fish, birds, mammals
• Larvae develop in crustaceans or insects
• No digestive tract

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Phylum Gastrotricha

• 800 species (freshwater marine)
• Similar to rotifers, but ventrally flattened with
  no corona or mastax
• Bristly or scaly
• 1 mm
• Interstitial spaces of benthic particles
• Glide using ventral cilia

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Phylum Entoprocta

• 150 species
• Most marine
• Urnatella gracilis
• Only common freshwater species in North America
• 5 mm
• Resemble hydroid cnidarians

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Phylogeny

• After deuterostomes diverged from protostomes,
  protostomes split
• Ecdysozoa
• Molt during development
• Lophotrochozoa
• Lophophore feeding (p.443)
• Trochophore-like larvae