BIOL 112 Lecture 31

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Lophotrochozoa

Annelida

Third type of worm: segmented (annelida = "little rings")

Marine, freshwater, and terrestrial habitats

3 Classes:

• Oligochaeta (earthworms)
• Polychaeta
• Hirudinea (leeches)

Characteristics:

• Closed circulatory system
  • blood vessels close to surface; gas exchange across skin (terrestrial) or gills (aquatic)
  • presence of septa between segments means coelomic fluid is restricted to a segment; hence need for closed circ. system
  • coelomic fluid acts as hydrostatic skeleton
• Characteristic peristaltic movement:
  • Circular muscle orientation (around worm body)
  • Longitudinal muscle orientation (along worm length)
  • c.f. Sinusoidal movement of nematodes

Polychaeta only:

• aquatic
• parapodia function as gills

Reproduction

Asexual

fragmentation

Worm breaks (cleaves; at same spot) into two new worms

Seasonal or in response to predators

Sexual

Mating between hermaphrodites

exchange sperm = cross-fertilization

Deuterostomia: Echinodermata

echino– = spiny, –derm = skin

2^nd degree pentaradial symmetry (5 arms or 5 sides)

• larvae are bilateral
• larvae grow into radially symmetric adult

dorsal anus, ventral mouth

Epidermis covers calcerous plates

Each arm/side has same anatomy

Adults are generally sessile or slow-moving, but larvae are motile.

Water-vascular system for locomotion:

• Water enters body through madreporite
• Travels along hydraulic canals
• Into tube feet (extension)
• Contact with surface causes contraction

Reproduction

Dioecious male/female organisms

gametes released into surrounding water