Phylum: Annelida - segmented worms

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Phylum Annelida - segmented worms
Class Oligochaeta
Class Polychaeta
Class Hirudinea
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Oligochaeta
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Class Polychaeta Bristle worm
is poisonous and attacks sea anemones
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Class Hirudinea
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Christmas tree worm
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Class Polycheata
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CLASS
P O L Y C H A E T A
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Yikes!!
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Characteristics of Phylum AnnelidaLittle rings

• True coelom
• Each compartment is surrounded by peritoneum
  which forms dorsal and ventral mesenteries that
  covers all the organs
• Hydrostatic skeleton
• Closed circulatory system

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True coelom
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Centralized Nervous System

• Brain
• Double ventral nerve cord
• Pair of ganglia in each segment
• Lateral nerves

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Centralized Nervous System
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Sensory organs

• Taste buds
• Statocysts - balance sensory receptor
• Photoreceptor eyes with lenses in some

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Circulatory System

• Blood flows entirely in closed vessels
• Some spp. have hearts
• Blood contains hemoglobin, which increases oxygen
  carrying ability

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Excretory system

• Pair of nephridia in each segment

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Respiration

• By gas exchange through
• Skin
• Gills
• Parapodia - fleshy paired appendages

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Body plan

• Bilateral
• Metameric-repeating segments
• (metamerism allows for budding)
• Setae-small hairs or sometimes parapodia, i.e.
  small appendages

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Body plan

• Setae (bristles) of chitin
• anchors for earthworm
• paddles for polychaete
• Enlarged as jaws in leeches, some polychaetes

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Reproduction

• Sexes are usually separate with gonads occurring
  in each segment
• Some species have gonad specific segments
• Breeding is usually seasonal (spring or fall)
• As gametes mature they fill the coelom and are
  released by the nephridia
• Fertilization can be internal or external
• Trochophore larvae develop, which are remarkably
  similar to the Molluscs

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Skin

• Contains glands to secrete mucous and setae

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Nutrition

• Eat any dead organic material
• Consume up to one half their body weight every
  day

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Nutrition

• Annelids range from carnivores, herbivores,
  scavengers, deposit feeders, and filter feeders
• With very few defenses, many remain in a burrow
  or secreted tube
• Carnivores can capture prey with strong jaws and
  quickly drag it back to its burrow
• Can use a muscular pharynx eversible proboscis

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Digestion

• mouth esophagus crop
• intestines gizzard
• Mechanical grinding in the gizzard
• Chemical in the intestines
• Extracellular and intracellular digestion

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Environmental role

• Can be found in fresh water, salt water, soil
• Helps aerate/renutrify gardens
• Medicinal purposes

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Classes

• How do we classify these segmented worms into
  different classes?

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Class Polychaeta (many setae or hairs)

• 20 setae per segment
• Well differentiated head
• Specialized sense organs
• Parapodia
• No clitellum
• Mostly marine predators, e.g. Barry the seaworm

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Class Polychaeta (many setae or hairs)
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Class Oligochaeta (Few long hairs)

• Clitellum
• Few long, short or straight setae 2-4 clusters
  per segment
• Land or marine, some parasites

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Class Oligochaeta (Few long hairs)
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Class Hirudinea

• Flattened dorsalventrally
• Mostly freshwater, some marine
• Fluid feeder (blood)
• Clitellum
• Setae have developed suckers
• Specialized proboscis

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Class Hirudinea

• Class Hirudinea
• pair of bladelike jaws
• posterior suction cup
• Predators
• External parasites, bloodsuckers
• Secrete anticoagulants
• Medicinal use

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Blood Sucker

• The salivary glands excrete hirudin which
  prevents the blood from coagulating
• May also secrete an anaesthetic and substance to
  dilate small blood vessels
• Blood is broken down by symbiotic bacteria that
  is then used by the leeches
• Leeches were commonly used in the 19th century
  for bloodletting
• Recent medical uses are to relieve pressure after
  vascular tissue is damaged
• Snake bites or the reattachment of a finger or ear