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Platyhelminthes

Simplest animals to have bilateral symmetry (milestone)

Soft-bodied, flat worms

Two Forms

Free Living

Parasitic

Platyhelminthes phylum is divided into three classes

Turbellaria

Trematoda

Cestoda

PlatyhelminthesClass: Tubellaria

Example: Planaria

Free Living“Cross-Eyed” wormsCan be up to 20 inches in lengthBottom Dwellers- feed on smaller animals and dead animals

Vary greatly in color, form, and size

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Platyhelminthes: Planarian

PlatyhelminthesClass: Trematoda

Example: Fluke

Resides in multiple hostsLives in digestive organs, liver, or blood of their primary hostUp to ½ inch in lengthCauses Schisteosomiasis

Eggs clog blood vessels, cause swelling and tissue decayCommon in undeveloped tropical areas that lack proper sanitary methods

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PlatyhelminthesClass: Cestoda

Example: Tapeworm

Live in the intestine of their primary hostSize range: very small to 15 meters in lengthCovered by a cuticle used for protection so that they don’t get digested in the intestine

Platyhelminthes: Tapeworm

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Platyhelminthes: Body Form & Skeleton

Bilateral SymmetryHydrostatic SkeletonAceolom

Platyhelminthes: Muscles & Locomotion

Free-Living Parasitic

Two methods1. Cilia on outside of body

- used for gliding through water

2. Muscle cells controlled by nervous system

- twist and turn motions

Adult form doesn’t move once it is attached to its primary host

Larva are able to swim in the water to find primary or intermediate host

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Platyhelminthes: Digestion

Free-Living Parasitic

Feed off of tiny aquatic animalsGastrovascular CavityPharynx -> Mouth -> Gut

Feed on blood, tissue fluidsGet nutrients from host’s digested food in intestine or other organsFluke: Pharynx Intestinal SacsTapeworm: doesn’t have a mouth, diffuses nutrients from host

Platyhelminthes: Respiration, Circulation, Excretion

Flat, thin bodies so they use diffusion to transport materialsno organs for respiration or circulation

Do have organs to remove liquid wasteFlame Cells – remove liquid waste from worm

Groups together to form a network of tubes and expel waste through pores in the body (nephridia)

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Platyhelminthes: Nervous System

Free-Living Parasitic

CephalizationGanglia

Two long nerve cords come off of the ganglia

Connected with lateral nerve cords (ladder-like structure)

Eyespots

Interact little with external environment so they have a very simple nervous system

Platyhelminthes: Reproduction - Free-Living

Sexual ReproductionMost are hermaphroditesTwo worms join, exchange sperm, eggs in each worm are fertilized, eggs are laid and hatch within a couple weeks

Asexual Reproduction = CommonBreak into parts using fissionEach part grows/develops the missing structures through regeneration

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Platyhelminthes: Reproduction - Parasitic - Fluke

Platyhelminthes: Reproduction - Parasitic - Tapeworm