Download Invertebrates 1

Invertebrates 3
Nematoda and Annelida
Phylum Nematoda:
The roundworms
Evolutionary relationships
Nematode body cavity:
pseudocoelom
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Mesoderm on inside of body wall, but not
surrounding gut
Body plan
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Feeding/digestive system
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Nematodes suck!
Complete digestive system
Gas exchange
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Body surface
Intestinal surface (minimal)
Body cavity (pseudocoelom)
No circulatory system
Excretory system/osmotic regulation
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Exists, not well-understood
Locomotion:
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Have only longitudinal muscles
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Demo: The nematode swim!
Body plan (cont.)
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Nervous system
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“Brain”: nerve ring
Four nerve cords (where?)
Ganglia along ventral cord
Unique connection of muscles and nerves
Sensory structures
Reproduction, etc…
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Reproduction
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Sexes usually separate, but some hermaphrodites
Internal fertilization
Many parasitic forms
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Trichina worms
Heartworms
River blindness
Elephantiasis
Also parasitic in plants
Phylum Annelida:
The segmented worms
Evolutionary relationships
Aceolomates, Pseudocoelomates
and Coelomates
Pseudocoelom
Coelom
 Surface area for
nutrient absorption
and gas exchange
+
+
Larger organs
Fluid cushions/
protects organs
Hydrostatic skeleton
is possible
+
+
+
+
+
+
Completely lined by
mesoderm
-
+
Mesenteries suspend
internal organs
Independent
movement of gut
-
+
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+
Basic Annelida features
 Have all features of protostomes
(know!)
 Have body segmentation (new feature)
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Repetition of body parts
Similar structures found in each region
Some specialization of regions
Some continuous parts (digestive system)
Annelid diversity
Class Polychaeta
Class Hirudinea
Class Oligochaeta
Body Plan (earthworm)
 Digestive system
 Complete
 Specialized regions
 Circulation
 Closed system
 Multiple hearts
 Gas exchange
 Body surface
 Coelom
 Parapodia
(Polychaetes)
 Excretory
 Metanephridia
Body Plan (cont.)
 Nervous system
 Brain (=cerebral
ganglia)
 Ventral nerve cord
(fused pair of cords)
 One ganglion per
segment
 Movement
 Peristalsis
 Setae
Feeding in different classes
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Class Oligochaeta: Earthworms
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Earth suckers (create vacuum by expanding muscular
pharnyx)
Why important in ecosystem?
Class Polychaeta: Marine segmented worms
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Many are tentacle feeders
Many other feeding modes
Class Hirudinea: Leeches
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Food suckers (create vacuum by expanding pharynx,
digestive tract)
How do blood sucking leeches feed?.
What three substances do blood sucking leeches
secrete to aid in the process?
NOTE: Not all leeches are blood suckers!