Invertebrates 2 Ctenophora Platyhelminthes Nematoda Lecture outline 1

Invertebrates 2 Ctenophora, Platyhelminthes, Nematoda

Lecture outline 1. 2. 3. Phylum Ctenophora (briefly) Phylum Platyhelminthes Phylum Nematoda

Phylogenetic overview (cont. )

Phylum Ctenophora: The comb jellies § Along with Cnidarians, they are radially symmetrical

Phylum Platyhelminthes: The flatworms

Evolutionary position: Development of a third germ layer and bilateral symmetry § Cnidarians, Ctenophores § Radial symmetry, diploblastic § (Porifera) All others Bilateral symmetry, triploblastic

Still no body cavity! § Platyhelminthes § § Porifera Cnidaria Ctenophora All others have body cavities

Basic Platyhelminthes features § § Eversible pharynx Gastrovascular cavity § § Water and ion balance Nervous system § § Structure Functions Unidirectional AP brain distinct nerve cords sensory organs Movement

Reproduction § Hermaphrodites § Internal fertilization § penis, sometimes with stylet § hypodermic impregnation § stab prey § R-rated flick…

§ The blood fluke Schistosoma infects 200 million people, leading to body pains, anemia, and dysentery. Fig. 33. 11 Copyright © 2002 Pearson Education, Inc. , publishing as Benjamin Cummings

§ Tapeworms (class Cestoidea) are also parasitic. § The adults live mostly in vertebrates, including humans. § Anterior suckers and hooks anchor the worm in the digestive tract of the host. § A long series of proglottids, sacs of sex organs lie posterior to the scolex. § Tapeworms absorb food particles from their hosts. Fig. 33. 12 Copyright © 2002 Pearson Education, Inc. , publishing as Benjamin Cummings

Phylum Nematoda: The roundworms

Evolutionary features: Body cavity! § Platyhelminthes § § Porifera Cnidaria Ctenophora Nematoda and all others!

Nematode body cavity: pseudocoelom § Mesoderm on inside of body wall, but not surrounding gut

Body plan § Feeding/digestive system: § § Gas exchange § § Body surface Coelomic cavity No circulatory system Excretory system/osmotic regulation § § Relatively simple (not highly branched) gut, but it is complete, with anus! Exists, not well-understood Locomotion: § Have only longitudinal muscles § Demo: The nematode swim!

Body plan (cont. ) § Nervous system § Four nerve cords: 1 dorsal, 1 ventral, and 2 lateral § ganglia along ventral cord (will see this in arthropods/annelids) § Sensory structures

Reproduction, etc… § Reproduction § § § Sexes usually separate, but some hermaphrodites Internal fertilization Many parasitic forms § § § Trichina worms Heartworms River blindness Elephantiasis Also parasitic in plants