Invertebrates 3 Nematoda and Annelida. Phylum Nematoda: The roundworms.

Invertebrates 3Invertebrates 3

Nematoda and AnnelidaNematoda and Annelida

Phylum Nematoda:Phylum Nematoda:The roundwormsThe roundworms

Evolutionary relationshipsEvolutionary relationships

Nematode body cavity: Nematode body cavity: pseudocoelompseudocoelom

Mesoderm on inside of body wall, but not Mesoderm on inside of body wall, but not surrounding gutsurrounding gut

Body planBody plan Feeding/digestive systemFeeding/digestive system

Nematodes suck!Nematodes suck! Complete digestive systemComplete digestive system

Gas exchangeGas exchange Body surfaceBody surface Intestinal surface (minimal)Intestinal surface (minimal) Body cavity (pseudocoelom)Body cavity (pseudocoelom) No circulatory systemNo circulatory system

Excretory system/osmotic regulationExcretory system/osmotic regulation Exists, not well-understood Exists, not well-understood

Locomotion:Locomotion: Have only longitudinal muscles Have only longitudinal muscles

Demo: The nematode swim!Demo: The nematode swim!

Body plan (cont.)Body plan (cont.)

Nervous systemNervous system ““Brain”: nerve ring Brain”: nerve ring Four nerve cords (where?)Four nerve cords (where?) Ganglia along ventral cordGanglia along ventral cord Unique connection of muscles and nervesUnique connection of muscles and nerves Sensory structuresSensory structures

Reproduction, etc…Reproduction, etc…

ReproductionReproduction Sexes usually separate, but some hermaphroditesSexes usually separate, but some hermaphrodites Internal fertilizationInternal fertilization

Many parasitic formsMany parasitic forms Trichina wormsTrichina worms HeartwormsHeartworms River blindnessRiver blindness ElephantiasisElephantiasis Also parasitic in plantsAlso parasitic in plants

Phylum Annelida:Phylum Annelida:The segmented wormsThe segmented worms

Evolutionary relationshipsEvolutionary relationships

Aceolomates, Pseudocoelomates Aceolomates, Pseudocoelomates and Coelomatesand Coelomates

PseudocoelomPseudocoelom CoelomCoelom

Surface area for Surface area for nutrient absorption nutrient absorption and gas exchange and gas exchange

++ ++

Larger organsLarger organs ++ ++

Fluid cushions/ Fluid cushions/ protects organsprotects organs

++ ++

Hydrostatic skeleton Hydrostatic skeleton is possibleis possible

++ ++

Completely lined by Completely lined by mesoderm mesoderm

-- ++

Mesenteries suspend Mesenteries suspend internal organsinternal organs

-- ++

Independent Independent movement of gutmovement of gut

-- ++

Basic Annelida featuresBasic Annelida features

Have all features of protostomes Have all features of protostomes (know!)(know!)

Have body segmentation (new feature)Have body segmentation (new feature) Repetition of body partsRepetition of body parts Similar structures found in each regionSimilar structures found in each region Some specialization of regionsSome specialization of regions Some continuous parts (digestive system)Some continuous parts (digestive system)

Annelid diversityAnnelid diversity

Class Polychaeta

Class Oligochaeta

Class Hirudinea

Body Plan (earthworm)Body Plan (earthworm) Digestive systemDigestive system

CompleteComplete Specialized regionsSpecialized regions

CirculationCirculation Closed systemClosed system Multiple heartsMultiple hearts

Gas exchangeGas exchange Body surfaceBody surface CoelomCoelom Parapodia Parapodia

(Polychaetes)(Polychaetes) ExcretoryExcretory

MetanephridiaMetanephridia

Body Plan (cont.)Body Plan (cont.) Nervous systemNervous system

Brain (=cerebral Brain (=cerebral ganglia)ganglia)

Ventral nerve cord Ventral nerve cord (fused pair of cords)(fused pair of cords)

One ganglion per One ganglion per segmentsegment

MovementMovement PeristalsisPeristalsis SetaeSetae

Feeding in different classesFeeding in different classes Class Oligochaeta: EarthwormsClass Oligochaeta: Earthworms

Earth suckers (create vacuum by expanding muscular pharnyx)

Why important in ecosystem? Class Polychaeta: Marine segmented wormsClass Polychaeta: Marine segmented worms

Many are tentacle feeders Many other feeding modes

Class Hirudinea: LeechesClass Hirudinea: Leeches 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!