Phylum Annelida

1
Phylum Annelida

• Segmented worms
• 3 Classes
• Polychaeta
• Oligochaeta
• Hirudinea

2
Characteristics

• 15,000 species (2/3 marine)
• Lophotrochozoan protostome coelomates spiral
  cleavage
• Nervous and circulatory systems more complex than
  in other worms
• Segmentation

3
Segmentation

• Annuli (circular grooves marking body segments)
• Metamerism (repetition of organs in segments
  called metameres or somites)
• Also occurs in arthropods and vertebrates
• Septa (walls separating segments)

4
Characteristics, cont.

• Setaetiny chitinous bristles (not in leeches)
• Short setaeanchoring
• Long setaeswimming

5
Body Wall

• Ends of body (not metameres)
• Prostomiumanterior
• Pygidiumterminal
• New metameres form in front of the pygidium

6
Body Wall, cont.

• Circular and longitudinal muscles underneath
• Epidermis and thin outer cuticle on surface

7
Coelom

• From mesodermal split on each side of gut
  (schizocoel)
• Peritoneum
• Lines body wall
• Forms dorsal and ventral mesenteries
• Adjacent segments meet, forming septa
• Gut, blood vessels extend through septa

8
Hydrostatic Skeleton

• Constant fluid volume
• Longitudinal muscles contract
• Body gets short and fat
• Circular muscles contract
• Body narrows and lengthens
• Fluid-filled coelom (not in leeches)

9
Hydrostatic Skeleton, cont.

• Force separated into sections
• Peristalsis (alternating contractions) allows
  burrowing
• Swimming annelids undulate

10
Class Polychaeta

• Diversity
• 10,000 species
• Most marine and benthic
• 1 mm to 3 m
• Head with sense organs

11
Diversity, cont.

• Parapodia (paired appendages) with bundles of
  setea
• No clitellum
• Niches
• Important in food chains as tube-dwellers or
  pelagic
• Free-moving, burrowing, crawling, or sedentary

12
Nutrition

• Foregut
• Stomodeum, pharynx, esophagus
• Midgut
• Secretes enzymes, absorbs nutrients
• Hindgut
• Leads to anus
• Food source depends on motility

13
Circulation/Respiration

• Networks of blood vessels in some
• Circulation via coelomic fluid in others
• Gas exchange through parapodia, gills, or body
  surface
• Many have respiratory pigments such as hemoglobin

14
Excretion

• Various forms of organs (nephridia)
• One pair per metamere
• Ceolomic fluid enters and selective resorption
  occurs along nephridial duct

15
Nervous/Sensory

• Double ventral nerve cord
• Ganglia in each metamere
• Varying eyes
• Nuchal organs (ciliated sensory
  pitschemoreceptive?)
• Statocysts

16
Reproduction/Development

• Monoecious
• No permanent sex organs
• Gonadstemporary
• External fertilization
• Trochophore larva

17
Clam Worms Nereis

• Low tide burrowers
• Search for food at night
• Mouth, jaws, sensory tentacles
• Small animals, other worms larvae
• Peristalsis moves food
• Parapodia
• 2 lobed with spines and blood vessels
• Creeping, swimming, undulating

18
Other Polychaetes

• Scale worms
• Fireworms
• Tube-dwellers
• Fanworms
• Parchment worm

19
Class Oligochaeta

• Diversity
• 3,000 species
• In soil and freshwater
• Few marine or parasitic
• Most have setae fewer than in polychaetes

20
Earthworms

• Burrow in moist soil
• Near surface when wet
• Deep dormant when dry
• Emerge at night

21
Earthworms, Importance

• Estimated 10-18 tons dry soil pass through
  intestines per acre per year
• Mix soil materials
• Add nutrients

22
Oligochaeta Nutrition

• Most scavengers
• Decayed organic matter, leaves, refuse
• Muscular pharynx sucks in food
• Muscular calciferous glands along esophagus
  control calcium ions in blood

23
Nutrition, cont.

• Food stored in crop
• Gizzard grinds food
• Digestion/absorption in intestine
• Typhlosole increases surface area

24
Nutrition, cont.

• Chloragogen tissue
• Synthesizes glycogen fat (eleocytes)
• Function in excretion

25
Circulation/Respiration

• Coelomic fluid blood carry food, wastes, gases
• Closed circulatory system
• 5 main trunks
• Dorsal vessel has valves (true heart)

26
Circulation/Respiration, cont.

• Dorsal vessel
• Pumps blood into 5 pairs of aortic arches
• Steady pressure into ventral vessels
• Ventral vessel delivers blood to nephridia,
  digestive tract, body walls

27
Circulation/Respiration, cont.

• Blood
• Colorless amoeboid cells
• Dissolved hemoglobin
• Earthworm gas exchange through moist skin (no
  special organs)

28
Excretion

• Most somites have metanephridia
• Wastes enter nephrostome
• Nephridial duct ends at bladder
• Bladder empties at nephridiopore
• Types of wastes
• Aquatictoxic ammonia
• Terrestrial--urea

29
Nervous/Sensory

• Earthworms
• CNS peripheral nerves
• 2 cerebral ganglia connect to ventral nerve cord
• Ganglia in each somite
• Sensory and motor fibers

30
Nervous/Sensory

• Neurohormones regulate
• Reproduction
• Secondary sex characteristics
• Regeneration
• No eyes
• Photoreceptors in epidermis
• Tactile nerve endings in tegument

31
Behavior

• Sensitive to stimuli
• Find food using chemical stimuli
• Avoid light
• Trial-and-error learning

32
Reproduction/Development

• Monoecious
• Immature sperm from testes
• Mature in seminal vesicles
• Pass to sperm ducts
• Eggs discharged by ovaries into coelom

33
Reproduction/Development, cont.

• Seminal receptacles receive, store sperm
• Mate during warm, moist weather
• Align in opposite directions, ventral surfaces
  together
• Clitellum secretes sticky mucus

34
Reproduction/Development, cont.

• Sperm travel to seminal receptacles of other worm
  along seminal grooves
• Worm secretes mucus tube chitinous band
  cocoon
• Eggs, albumin, sperm pour into cocoon
• Cocoon passes forward
• Fertilization in cocoon young worms emerge

35
Freshwater Oligochaetes

• Smaller with longer setae than earthworms
• Important fish food
• Few ectoparasites

36
Class Hirudinea (Leeches)

• Diversity
• Most freshwater
• More tropical than temperate
• Most flattened
• Some carnivores some parasites
• Suckers rather than setae

37
Form and Function

• Usually have 34 somites
• No septa
• Coelomic cavity filled with connective tissue and
  spaces (lacunae)
• Locomotion using suckers to inchworm

38
Nutrition

• Freshwaterhave proboscis
• Ingest small invertebrates or suck blood
• Terrestrial
• Eat insect larvae, earthworms, slugs
• Parasitic on baby birds

39
Nutrition, cont.

• Medicinal leecheswrongly believed disorders
  caused by excess blood

40
Respiration/Excretion

• Exchange gases across skin
• Some fish leeches have gills
• 10 to 17 pairs of nephridia

41
Nervous/Sensory Systems

• 2 brains
• Fused ganglia form ring around pharynx
• Fused ganglia at posterior
• Epidermis
• Sensory nerve endings
• Photoreceptor cells

42
Reproduction

• Hermaphroditic
• Cross-fertilize
• Clitellum
• Appears during breeding season
• Secretes cocoon to receive sperm and egg
• Cocoons buried in mud

43
Circulation

• Some oligochaete-type circulatory system
• Coelomic system (lacunae) -- auxiliary
• Some lack blood vessels
• Coelomic sinuses -- vascular system