PLATYHELMINTHES, ET AL.CHAPTER 8, 9, 10

FLATWORMS?

ACOELA▸ phylum acoelomorpha ▸ considered basal to all other

bilateria ▸ marine or brackish ▸ usually found in sediments

ACOELOMORPHA

ACOELA▸ Digestion▸ some with gastrovascular cavity

▸ Reproduction ▸ Radial nerve system

proboscis sheath

statocyst

testes

gut

mouth

ovary

gonopore

PLATYHELMINTHES

FLATWORMS▸ Phylum Platyhelminthes—platy-flat, helmins-worm ▸ Free-living or parasitic ▸ Acoelomate with primary bilateral symmetry ▸ Triploblastic ▸ Organ level of development ▸ Bilateral symmetry ▸ useful for motile, directional animals ▸ Ventral/dorsal ▸ anterior/posterior ▸ right/left

PLATYHELMINTHES

radial symmetry

bilateral symmetry

PLATYHELMINTHES

▸ Structure and Function ▸ Excretion and Osmoregulation ▸ Protonephridia ▸ Flame cells ▸ Wastes are released through nephridiopore

Tubule

Tubules of

protonephridia

Cilia

Interstitial

fluid flow

Opening in

body wall

Nucleus

of cap cell

Flame

bulb

Tubule cell

PLATYHELMINTHES

▸ Nutrition and Digestion ▸ Carnivorous or parasitic ▸ Sac-like g-v cavity with single mouth opening ▸ rhabdocoela ▸ triclad ▸ polyclad

Gastrovascularcavity

Mouth

Eyespots

Ganglia Ventral nerve cords

Pharynx

PLATYHELMINTHES

▸ Nervous system and sense organs ▸ Range in complexity ▸ from nerve-net pattern to cerebral ganglia / paired nerve

cordsGastrovascularcavity

Mouth

Eyespots

Ganglia Ventral nerve cords

Pharynx

PLATYHELMINTHES

▸ Reproduction ▸ Asexual ▸ Sexual

▸ Movement ▸ most glide along

mucous film using cilia ▸ rhabdites.

▸ in some, outer layer of the body is syncytial (tegument) ▸ lacks cilia.

▸ circular, longitudinal and diagonal muscles

ciliummicrovilli

muscle

nerve

parenchyma

viscid glands

releasing gland

epithelial cell

anchor cell

•viscid gland cells•releasing gland cells•anchor cells

GROUPS

CLASSIFICATION▸ Class Turbellaria ▸ Mostly free-living ▸ using ventral cilia to crawl along mucus or sometimes

swimming ▸ Marine or freshwater

TURBELLARIA

▸ Predatory or detritivorous ▸ Amazing regenerative

powers ▸ neoblasts

▸ Sexual Reproduction ▸ monoecious ▸ reciprocal sperm

transfer ▸ direct development

TREMATODA

spine

distal cytoplasm

muscle

golgi

nucleustegument cell body

mitochondrion

parenchymal cell

FLUKES▸ Class Trematoda—flukes ▸ Vertebrate endoparasites ▸ Adhesive sucker(s) or

hooks ▸ Often with a multi-stage

life cycle ▸ example life cycle ▸ overview -- egg ->

miracidium -> sporocyst -> redia -> cercaria (secondary larvae) -> metacercaria (eaten by primary host)-> adult

TREMATODA

▸ liver fluke life cycle ▸ eggs passed in feces ▸ Freshwater snail eats

eggs ▸ Miracidium transforms

into a sporocyst ▸ Redia reproduce

asexually ▸ Cercaria leave snail,

burrow into fish ▸ Metacercaria are eaten

MIND CONTROL!!!

▸ Dicrocoelium dendriticum

TREMATODA

▸ Some fluke cercariae enter humans directly ▸ schistosome dermatitis

or “swimmer’s itch”

TREMATODA

Human host

Motile larva

Snail host

Ciliated larva

Male

Female

1 mm

sexual reproduction in host

larvae infect snails

asexual reproduction in snail

larvae burrow into human

▸ Tropical blood flukes ▸ survive and use

humans as hosts ▸ dioecious ▸ gynecophoric

canal

MONOGENIC FLUKES

▸ Class Monogenea— ▸ Single host ▸ oncomiracidium (ciliated larva) ▸ opisthaptor

prohaptor

mouth

suckeropisthaptor

anchor

CESTODES

▸ Class Cestoda—tapeworms ▸ Gut parasites of vertebrates ▸ Monoecious ▸ No gut ▸ Microtriches

thus the area for absorption of nutriments. The bases ofspine-like and blade-like microtriches have an electron-dense ridge at their anterior edge. According toMacKinnon and Burt (1983 ) this ridge may function inpreventing the microtriches from bending forward andthus losing their grip against the mucosal epithelium ofthe host intestine.

The ultrastructure of microtriches can be used as ataxonomic character to be added to other characteristics(Richmond and Caira 1991; Hoberg et al. 1995 ; Cairaand Tracy 2002; Ivanov and Brooks 2002; Ivanov 2004 ;Gil de Pertierra 2004 , 2005 ). In our opinion moreinformation of microtriches pattern could be useful forthe determination of species in proteocephalideans.

101

cytoplasm of tegumentmicrotrich

circular musclelongitudinal musclemitochondria

CESTODES

▸ Scolex ▸ two dorsal nerve cords

▸ Proglottids ▸ New proglottids

originate behind scolex

CESTODES

▸ mature proglottids ▸ become egg sacs that are

passed in feces ▸ life cycle ▸ Eggs hatch into larvae -->

eaten by an intermediate host and encyst in muscle

▸ Larvae called cysticercus larvae

▸ Undercooked flesh eaten by the primary host

▸ Inverted scolex of larva then everts in definitive host’s gut

CESTODES

▸ mature proglottids ▸ become egg sacs that are passed in feces

▸ life cycle ▸ Eggs hatch into larvae --> eaten by an intermediate host and

encyst in muscle ▸ Larvae called cysticercus larvae ▸ Undercooked flesh eaten by the primary host ▸ Inverted scolex of larva then everts in definitive host’s gut

CESTODES

▸ many diverse live cycles

TEXT

▸ Tapeworm diet?▸ metamerism? ▸ strobila ▸ germinative zone

brain from a 9 year old infected with pork tapeworm

CHAPTER 9

MESOZOA▸ Phylum Mesozoa -- ▸ rhombozoans ▸ orthonectids

orthonectid

?

CHAPTER 10

▸ Clade Gnathifera ▸ Phylum Gnathostomulida ▸ acoelomate ▸ no circulatory system ▸ ciliated epidermal cells ▸ jaws with bilateral symmetry

ovary

testes

ROTIFERS

▸ Phylum Rotifera—rotifers ▸ general characteristics ▸ mastax (trophi) ▸ Marine or freshwater

suspension-feeders ▸ some colonial ▸ may be floaters,

creepers, or sessile

ROTIFERS

▸ Structure and function ▸ eutely ▸ syncytial epidermis with cuticle ▸ lorica = shell

▸ wheel organ ▸ metachronal ciliary motion

▸ Bilobed “brain” with paired nerves ▸ Paired eyespots

▸ large pseudocoel ▸ protonephridia ▸ circular and longitudinal muscles ▸ Foot with pedal glands ▸ 1-4 toes

corona

brain

eyespot

flame bulb

mastax

gastric gland

salivary glands

stomach

germovitellarium

intestine

cloacal bladder

anus

pedal glands

toe

ROTIFERS

▸ classes ▸ bdelloidea ▸ seisonidea

(seisonacea) ▸ monogononta

ROTIFERS

▸ sex determination ▸ TSD ▸ GSD ▸ haplodiploidism

ROTIFERS

▸ bimodal reproduction ▸ class monogononta

▸ Mixis ▸ Amictic females produce

diploid eggs ▸ mictic stimulus -- Mictic

females --> haploid eggs ▸ unfertilized eggs become

haploid males ▸ Fertilized eggs become

dormant

ACANTHOCEPHALA

▸ Phylum Acanthocephala ▸ proboscis with spiny

hooks ▸ no digestive tract

▸ protonephridia ▸ dioecious ▸ syncytial outer surface ▸ lacunar system

distributes nutrients ▸ Recent work puts this

group within the Rotifers

▸ life cycle

ACANTHOCEPHALA

▸ probably evolved from rotifers

GASTROTRICHS

▸ other Lophotrochozoa ▸ Phylum Gastrotricha ▸ brackish, salt, or freshwater ▸ rotifer-like -- but no corona ▸ protonephridia ▸ no flame cells ▸ solenocytes (single

flagellum)