Invertebrates 2Invertebrates 2

Ctenophora, Platyhelminthes, Ctenophora, Platyhelminthes, Nematoda Nematoda

Lecture outlineLecture outline

1.1. Phylum Ctenophora (briefly)Phylum Ctenophora (briefly)

2.2. Phylum PlatyhelminthesPhylum Platyhelminthes

3.3. Phylum NematodaPhylum Nematoda

Phylogenetic overview (cont.)Phylogenetic overview (cont.)

Phylum Ctenophora: The Phylum Ctenophora: The comb jelliescomb jellies

Along with Cnidarians, they are Along with Cnidarians, they are radially symmetricalradially symmetrical

Phylum Platyhelminthes:Phylum Platyhelminthes:The flatwormsThe flatworms

Evolutionary position: Evolutionary position: Development of a third germ Development of a third germ layer and bilateral symmetrylayer and bilateral symmetry

Cnidarians, Ctenophores All others Cnidarians, Ctenophores All others Radial symmetry, diploblastic Bilateral symmetry, triploblastic Radial symmetry, diploblastic Bilateral symmetry, triploblastic

(Porifera)(Porifera)

Still no body cavity!Still no body cavity!

Platyhelminthes All others have body cavitiesPlatyhelminthes All others have body cavities Porifera Cnidaria Porifera Cnidaria

CtenophoraCtenophora

Basic Platyhelminthes featuresBasic Platyhelminthes features

Eversible pharynxEversible pharynx Gastrovascular cavityGastrovascular cavity

StructureStructure FunctionsFunctions

Water and ion balanceWater and ion balance Nervous systemNervous system

Unidirectional APUnidirectional AP brainbrain distinct nerve cords distinct nerve cords

sensory organssensory organs MovementMovement

ReproductionReproduction

HermaphroditesHermaphrodites Internal fertilizationInternal fertilization

penis, sometimes with styletpenis, sometimes with stylet hypodermic impregnationhypodermic impregnation stab preystab prey

R-rated flick…R-rated flick…

The blood flukeThe blood flukeSchistosomaSchistosoma infects 200 infects 200 million people,million people,leading to body leading to body pains, anemia, pains, anemia, and dysentery.and dysentery.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 33.11

Tapeworms (class Cestoidea) Tapeworms (class Cestoidea) are also parasitic.are also parasitic. The adults live mostly in The adults live mostly in

vertebrates, including humans.vertebrates, including humans. Anterior suckers and hooks Anterior suckers and hooks

anchor the worm in the anchor the worm in the digestive tract of the host.digestive tract of the host.

A long series of proglottids, A long series of proglottids, sacs of sex organs lie posterior sacs of sex organs lie posterior to the scolex.to the scolex.

Tapeworms absorb food Tapeworms absorb food particles from their hosts. particles from their hosts.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 33.12

Phylum Nematoda:Phylum Nematoda:The roundwormsThe roundworms

Evolutionary features:Evolutionary features:Body cavity!Body cavity!

Platyhelminthes Nematoda and all others!Platyhelminthes Nematoda and all others! Porifera Cnidaria Porifera Cnidaria

CtenophoraCtenophora

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 system:Feeding/digestive system:

Relatively simple (not highly branched) gut, but it Relatively simple (not highly branched) gut, but it is complete, with anus!is complete, with anus!

Gas exchangeGas exchange Body surfaceBody surface Coelomic cavityCoelomic cavity 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 Four nerve cords: 1 dorsal, 1 ventral, and Four nerve cords: 1 dorsal, 1 ventral, and

2 lateral2 lateral ganglia along ventral cord (will see this in ganglia along ventral cord (will see this in

arthropods/annelids)arthropods/annelids)

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