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)