ZOO 115 Invertebrate Zoology

Phylum Platyhelminthes

Classes

Turbellaria Free-living flatworms

Mongenea Mongenetic flukes - parasitic

Trematoda Flukes- parasitic

Cestoda Tapeworms- parasitic

Phylum Platyhelminthes

© David Luquet

/gecko.gc.maricopa.edu/~lsola/bio182/labreview/

/gecko.gc.maricopa.edu/~lsola/bio182/labreview/

www.pbs.org/kcet/shapeoflife/imganim//gecko.gc.maricopa.edu/~lsola/bio182/labreview/

Ed T. Schmidtmann, USDA/ARS.

www.islandream.com/wakatobi/flatworm02.jpg

Phylum Platyhelminthes

About 20,000 sp. Substrate crawlers in both marine and freshwater Mostly small and soft-bodied Lack a circulatory system

Diffusion limited Controversy about phylogeny

PlatyhelminthesClass Turbellaria

Virtually all are aquatic with most being marine

Most are bottom dwellers but there are some pelagic forms

www.seafriends.org.nz/enviro/habitat/f017217t.jpg

Body

Skeleton – weblike sheet of actin filaments

Outer-layer is a ciliated epidermis

Secrete Rhabdites Thought to be important in

locomotion, cocoon development and predator repellant

Body

Mesenchyme – Hydraulic action on larger organisms

Parenchyma – connective tissue compartment between body wall, musculature and gut. Neoblasts - wound

repair and regeneration Chromatophores may

be present and under control by brain.

zoology.unh.edu/faculty/litvaitis/Flatworms/muscles.jpg

zoology.unh.edu/faculty/litvaitis/Flatworms/muscles.jpg

Gland cells

Gland cells

Nervous system

Bilaterial or Ring like brain Longitudinal nerves

Nerve net

Nervous system - sensory

Ocelli Some have statocysts in the head region

Chemoreceptors over entire body

Cilia mechanoreceptors

Musculature

zoology.unh.edu/faculty/litvaitis/Flatworms/muscles.jpg

Longitudinal muscles

Circular muscles

Dorsoventral muscles

Also have diagonal muscles – not shown

How do they move?

Ciliary creeping Muscular creeping Swimming Peristalsis Twisting, turning, extension and retraction Somersaulting

Complete Bilateral gut

www.emc.maricopa.edu/faculty/farabee/BIOBK/flatworm.gifwww.emc.maricopa.edu/faculty/farabee/BIOBK/flatworm.gif

zoology.unh.edu/faculty/litvaitis/Flatworms/muscles.jpg

Gut

Most are carnivores and scavengers Some Aoela have zooxanthellae

Feeding and digestion

Sense prey using chemreceptors and mechanoreceptors

Capture prey Wrapping themselves around prey Entangling it in slime Pinning prey with adhesive glands Some have toxic mucus Some use penis

Food swallowed by pharynx or

www.emc.maricopa.edu/faculty/farabee/BIOBK/flatworm.gif

Proteolytic enzymes are injected into prey and pharynx is used to pump liquified contents.

Gut types Acoela – syncytial mass enclosed by membrane Simple unbranched sac Multiple lateral branches

Gland cells in gut supply additional enzymes.

Digestive cells phagocytize remainder

Excretion

www.lifesci.utexas.edu/faculty/sjasper/images/protonephridia.jpg

Reproduction

Regeneration Clonal Reproduction – longitudinal fission

Reproduction

Sexual Reproduction Most hermaphrodites Most copulation and internal fertilization Male

1 or more pairs of testis Ducts, storage area Penis – may have stylet

Female I or more pairs of ovaries Copulatory bursa (vagina), seminal receptacle, uterus

Reproduction

Development Some freshwater species produce summer

and winter eggs Usually egg->blastula->gastrula->juvenile-

>adult Marine polyclads produce planktonic larvae

Generation time: 16-75 days Life span: 65-140 days

Platyhelminthes – Dueling Penises

Penis

Wounds