Phylum Platyhelminthes – Diversity and Characteristics Phylum Characteristics: flattened, acoelomate bodies; triplo- blastic protostomes; parasitic forms with protective external body covering (syncytial tegument) Diversity & Class Characteristics (likely a paraphyletic group) Class Turbellaria: free-living flatworms with ciliated epidermis; ventral mouth near center of body; intestine w/o anus Class Trematoda: endoparasitic flukes; sucker(s) w/o hooks; 1° host a mollusk, final host a vertebrate Class Monogenea: flukes with posterior attachment organ (opisthaptor); most are ectoparasites (esp. fish gills & skin) Class Cestoda: tapeworms; body divided into series of seg- ments (proglottids); lack digestive system; scolex with suckers and/or hooks; endoparasites of vertebrate digestive systems; length can reach 50 feet

Class Turbellaria (Free-living Flatworms)

Class Trematoda (Endoparasitic Flukes) Human Lung Fluke  Human Liver Fluke

Class Monogenea (Ectoparasitic Flukes) and Class Cestoda (Tapeworms)

Fig Figure 14.5

Phylum Nematoda – Diversity and Characteristics Phylum Characteristics: smooth, rounded, pseudocoelomate bodies; protostomes; flexible cuticle covering body is molted (ecdysis); one-way digestive system (mouth  anus); dorsal and ventral nerve cords; found in nearly all environments; many are common endoparasites) Representative Roundworms Ascaris lumbricoides – common intestinal parasite; eggs in soil can be ingested (ex. uncooked vegetables, unwashed hands) Hookworms (ex. Necator americanus) – suck blood from intestinal wall Trichinella worms – infection of muscle tissue in final stages; can be fatal; trichinosis usually from eating undercooked pork Pinworms (ex. Enterobius vermicularis) – most common nematode infection; adults in large intestine; females lay eggs at night (anus) Filarial worms – infect lymphatic system; spread via mosquitos/flies; cause elephantiasis, river blindness, and canine heartworm Caenorhabditis elegans – important model organism, especially regarding development (see page 386 re. Sydney Brenner)

N.A. Cobb (1914) – From Your Text If all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable; and if, as disembodied spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes, and oceans represented by a thin film of nematodes. The location of towns would be decipherable, since for every massing of human beings there would be a corresponding massing of certain nematodes. Trees would still stand in ghostly rows representing our streets and highways. The location of the various plants and animals would still be decipherable, and, had we sufficient knowledge, in many cases even their species could be determined by an examination of their erstwhile nematode parasites.

Fig Figure 18.1

Fig Figure 18.2

Fig. 18.5a

Fig. 18.4b Figure 18.4

Fig. 18.6

Fig Figure 18.7

Fig. 18.8

Fig Figure 18.10

Lymphatic Filariasis in Haiti

Other Non-segmented “Worms” Phylum Mesozoa: most are parasites of cephalopods; composed of only cells Phylum Nemertea: ribbon worms; marine predators; capture prey with long eversible proboscis Phylum Acanthocephala: spiny headed worms; intestinal parasites of vertebrates Phylum Phoronida: live in chitinous tubes; feed with lophophore (crown of ciliated tentacles encircling mouth but not anus) Phylum Kinorhyncha: marine worms; retractable head; spiny trunk with 11 segments Phylum Nematomorpha: “horsehair worms”; very long and slender; parasites of arthropods Phylum Priapulida: marine worms; burrow in sediments; detritus feeders or predators

Fig Figure 15.2

Fig Figure 18.1

Fig Chapter 14.25

Phylum Nemertea (Figures & 14.29)

Phylum Acanthocephala (left) and Phylum Phoronida (right)

Other Ecdysozoan Worms (Ch. 18) Kinorhyncha (left), Nematomorpha (top right), and Priapulida (bottom right)