Flatworms and Roundworms

ANCESTRALPROTIST

Porifera

Ctenophora

Cnidaria

Acoela

True Tissues

Metazo

a

Eu

metazo

a

Bilateria

Hemichordata

Echinodermata

Chordata

Platyhelminthes

Rotifera

Ectoprocta

Brachiopoda

Mollusca

Annelida

Nematoda

Arthropoda

Deu

tero

stom

ia

Lo

ph

otro

cho

zoa

Ecd

ysozo

a

Single common animal ancestor

prot

osto

mes

inve

rteb

rate

s

•Bilateral at some point•Usually cephalized •Triploblastic development

Terms of location (for bilateral organsims)

FLATWORMS (phylum platyhelminthes)

• Flattened body plan– Puts all cells close to ext. env. or GVC– No need for respiratory or circulatory systems– Gas exchange across ext. surface and gastrodermis

• Free living• Parasitic forms• Aceolomates (no body cavity)• Most belong to Rhabditophora

Digestive System• Gastrovascular Cavity—incomplete digestive

system• Highly branched (diverticula)• Functions– Digestive chamber • most digestion occurs extracellularly

– distributes nutrients

Excretory System & Water Balance• Protonephridia • flame bulbs internal external env. through pores• In freshwater species for maintaining water balance• Some parasitic flatworms are isotonic with host and

protonephridia eliminate nitrogenous waste

• Interstitial fluid cap cell of flame bulb eliminated via ducts and pores

• Nervous System:– Dual ventral nerve cords– “brain of ganglia”

• Reproduction;– Mostly cross fertilizing hermaphrodites– Some parasitic forms are dioecious

CNS

Planariafree living Rabditophora

• FREE LIVING RABDITOPHORA• predators and scavengers• move w/ ventral cilia & mucus• Sense Organs & NS

– Photoreceptors (eyes)– Lateral flaps (auricles) that are chemoreceptor's

Trematodes• Intermediate and final (ultimate) host– Blood flukes (schistosoma), liver flukes

• epicuticle of proteins and lipids instead of epidermis– digestion by the digestive enzyme in hosts

Schistosoma: unique among trematodes; are dioecious with distinct sexual dimorphismLarge male that surrounds femaleFemale is enclosed within the males gynacophoric canal for entire life of worms where they reproduce sexually.

Figure 33.11Humanhost

Male

Female

1 mm

Mature flukes

Ciliatedlarva

Motilelarva

Snail host

Tapeworms• Mostly inside vertebrates• Scollex for attachment• No GVC; direct absorption of nutrients• Proglottids = reproductive segments• Reproduction is usually sexual between proglottids of

adjacent individuals

Tapeworms

Roundworms (phylum Nematoda)Bilateria-protostoma-ecdysozoa

• Cyclinderical shaped bodies that taper to tips at both ends• Psuedocoel• Usually dioecious• Free living in soil, fresh, and salt water

– decomposers: important ecological role as decomposers• Many important parasitic forms

– Parasitize crop plants– Parasitize humans (~50 species)

• e.g., trhinella spiralis—trichinoisis

– Parasitize non-human animals– Parasitic forms manipulate host cells

BODY COVERING• Cuticle (collagen based) that must be shed– Ecdysis/molting

GAS AND WASTE EXCAHNGE• Directly across body wall (gas & nitrogenous

wastes)• Some species w/ glands to excrete salt

No circulatory system• Nutrients transported by fluid in psuedocoel.

Digestive System

• Complete digestive tract (alimentary canal)• Continuous feeding• Specialized regions/organs– Mouth, sucking pharynx, intestines, rectum, anus– Contents propelled by body movements

Nervous system• 4 nerve cords + “brain” of neuron cluster

surrounding pharynx. • ventral nerve largest

Muscles:• Longitudinal muscles only • Psuedocoel acts as a hydrostatic skeleton

Schistosomiasis, also known as bilharzia, snail fever, and Katayama fever

Schistosomiasis affects almost 210 million people worldwide,[5] and an estimated 12,000[6] to 200,000 people die from it a year.[7] The disease is most commonly found in Africa, as well as Asia and South America.[3] Around 700 million people, in more than 70 countries, live in areas where the disease is common.[7][8] Schistosomiasis is second only tomalaria, as a parasitic disease with the greatest economic impact.[9] It is classified as a neglected tropical disease.[10]