Bilaterally Bilaterally Symmetrical WormsSymmetrical Worms

Platyhelminthes, Nemertea, Platyhelminthes, Nemertea, Nematoda, Annelida, and Nematoda, Annelida, and

4 unique groups4 unique groups

Anatomical Sides of a Bilateral Anatomical Sides of a Bilateral OrganismOrganism

Anterior – Anterior – front side of an organism where the front side of an organism where the head with a brain or nerve net is locatedhead with a brain or nerve net is located

Posterior – Posterior – the rear side of an organismthe rear side of an organism (really the only way to tell for sure is that it is the (really the only way to tell for sure is that it is the side opposite from the head region)side opposite from the head region)

Dorsal – Dorsal – the back surface of an organismthe back surface of an organism Ventral – Ventral – the underside or belly region of an the underside or belly region of an

organismorganism

Anatomical Sides of a Radial vs Anatomical Sides of a Radial vs Bilateral OrganismBilateral Organism

Phylum PlatyhelminthesPhylum PlatyhelminthesCharacteristics:Characteristics:

– have bilateral symmetry have bilateral symmetry – have a have a vermiformvermiform (wormlike shape) (wormlike shape) – have a third layer of cells (the have a third layer of cells (the mesodermmesoderm) )

The mesoderm produces muscular layers, an The mesoderm produces muscular layers, an excretory system, and an elaborate reproductive excretory system, and an elaborate reproductive system. system.

– exhibit an exhibit an acoelomateacoelomate body plan body plan

PlatyhelminthesPlatyhelminthesPlatyhelminthes vs CnidariansPlatyhelminthes vs Cnidarians

Platyhelminthes are composed of Platyhelminthes are composed of 33 cell layers where as Cnidarians are cell layers where as Cnidarians are only composed of only composed of 22

ectodermectoderm is responsible for the production of is responsible for the production of much of the sensory system and surface much of the sensory system and surface skin (among other things) skin (among other things)

endodermendoderm contributes to the growth of contributes to the growth of structures such as the lining of the gut structures such as the lining of the gut

mesodermmesoderm is used to build muscular, is used to build muscular, excretory, and reproductive systems excretory, and reproductive systems

PlatyhelminthesPlatyhelminthesThe increases in complexity compared The increases in complexity compared

to Sponges, Cnidarians, and to Sponges, Cnidarians, and Ctenophora have led to increases in Ctenophora have led to increases in mobility, higher activity, and general mobility, higher activity, and general increase in responsiveness of the increase in responsiveness of the organisms from this phylum organisms from this phylum

PlatyhelminthesPlatyhelminthes Platyhelminths are commonly known as Platyhelminths are commonly known as

"flatworms," due to their almost paper-thin "flatworms," due to their almost paper-thin structure. structure.

They have a incomplete digestive system – They have a incomplete digestive system – meaning they have only one opening for meaning they have only one opening for the mouth and the anus.the mouth and the anus.

They typically undergo sexual They typically undergo sexual reproduction but can also reproduce reproduction but can also reproduce asexually by regeneration.asexually by regeneration.– Most species are hermaphrodites (contain both Most species are hermaphrodites (contain both

male and female parts)male and female parts)

3 Major Classes of 3 Major Classes of PlatyhelminthesPlatyhelminthes

1.1. TURBELLARIANTURBELLARIAN – free-living– free-living

2.2. TREMATODA – parasitic TREMATODA – parasitic

3.3. CESTODA – parasitic CESTODA – parasitic

CLASS TURBELLARIANCLASS TURBELLARIAN 3000 species 3000 species most marine most marine ex. planaria (fresh water)ex. planaria (fresh water)

CLASS TURBELLARIAN - CLASS TURBELLARIAN - PlanarianPlanarian

External anatomy External anatomy – anterior end spade shaped anterior end spade shaped – posterior end tapered posterior end tapered – body covered with cilia body covered with cilia

Movement Movement – move by undulative motion or move by undulative motion or – laying down mucus layer and beating cilia laying down mucus layer and beating cilia

Digestion and excretion Digestion and excretion – scavenger (carrion) scavenger (carrion) – predator (small prey) predator (small prey)

CLASS TURBELLARIAN - CLASS TURBELLARIAN - PlanarianPlanarian

Digestion Digestion – muscular pharynx extended out of mouth muscular pharynx extended out of mouth – food sucked in food sucked in – passed into intestines (branched) passed into intestines (branched) – nutrients absorbed through intestinal wall or nutrients absorbed through intestinal wall or

phagocytosis phagocytosis – undigested food excreted through pharynx and undigested food excreted through pharynx and

mouth mouth Excretion Excretion

– chemical wastes and excess water eliminated by chemical wastes and excess water eliminated by network of ducts (pores and canals) network of ducts (pores and canals)

– contains flame cells contains flame cells – flame cells enclose a tuft of beating cilia flame cells enclose a tuft of beating cilia – cilia moves wastes into the ducts -> cilia moves wastes into the ducts -> – excretory pores - > outexcretory pores - > out

CLASS TURBELLARIAN - CLASS TURBELLARIAN - PlanarianPlanarian

Nervous control Nervous control – organizedorganized– sense light intensity and direction sense light intensity and direction – two anterior eyespots (photosensitive cells) two anterior eyespots (photosensitive cells) – touch, taste, and smell receptors touch, taste, and smell receptors – two anterior ganglia (clusters of nerves) -> simple two anterior ganglia (clusters of nerves) -> simple

brain brain – capable of simple "learning" capable of simple "learning" – memory stored chemically memory stored chemically

CLASS TURBELLARIAN - CLASS TURBELLARIAN - PlanarianPlanarian

Reproduction Reproduction – hermaphrodites hermaphrodites – sexual reproduction sexual reproduction

simultaneous fertilization simultaneous fertilization protective encapsulated eggs stick to rock protective encapsulated eggs stick to rock hatch 2-3 weeks hatch 2-3 weeks Mating season is February – MarchMating season is February – March

– asexual (summer) asexual (summer) attach to rock surface with posterior end attach to rock surface with posterior end stretch until they tear into two stretch until they tear into two each half regenerates lost parts each half regenerates lost parts

CLASS TURBELLARIAN - CLASS TURBELLARIAN - PlanarianPlanarian

CLASS TURBELLARIAN - CLASS TURBELLARIAN - PlanarianPlanarian

CLASS TREMATODACLASS TREMATODA 6,000 species 6,000 species parasitic - both endoparasites and parasitic - both endoparasites and

ectoparasites ectoparasites leaf shaped leaf shaped eg. flukes eg. flukes

CLASS TREMATODA - FlukeCLASS TREMATODA - Fluke– parasites parasites – 1 cm long (oval shaped) 1 cm long (oval shaped) – 2 sucker mouths (anterior and ventral) 2 sucker mouths (anterior and ventral) – cling to host cling to host – anterior sucker sucks in blood, cells and anterior sucker sucks in blood, cells and

fluids of hostfluids of host

CLASS TREMATODA - FlukeCLASS TREMATODA - Fluke Nervous and Excretory system Nervous and Excretory system

– Turbellarian like Turbellarian like Reproduction Reproduction

– complex reproductive life cycle complex reproductive life cycle – hermaphroditic hermaphroditic – long coiled uterus (stores 10,000+ eggs) long coiled uterus (stores 10,000+ eggs) – eggs released through genital pore -> eggs released through genital pore ->

larvae larvae

TREMATODA – Fluke Life CycleTREMATODA – Fluke Life Cycle

CLASS CESTODACLASS CESTODA 1,500 species1,500 species Also known as Also known as TAPEWORMSTAPEWORMS most are parasitic (7 in humans) most are parasitic (7 in humans) adapted for parasitic life adapted for parasitic life tough outer tegument tough outer tegument hooks and suckers hooks and suckers

CLASS CESTODACLASS CESTODA nervous system extends length of body nervous system extends length of body lack sense organs, mouth, and digestive lack sense organs, mouth, and digestive

tract tract absorb nutrients directly through heavily absorb nutrients directly through heavily

folded tegument knoblike head with hooks folded tegument knoblike head with hooks and suckers (scolex) and suckers (scolex)

grows by producing body segments grows by producing body segments (proglottids) (proglottids)

oldest proglottids at posterior oldest proglottids at posterior

CLASS CESTODACLASS CESTODA Life cycle and reproduction Life cycle and reproduction

– proglottids contain both male and proglottids contain both male and female reproductive organs female reproductive organs

– cross fertilization is typical between cross fertilization is typical between individuals or proglottids individuals or proglottids

– after fertilization - proglottids break off after fertilization - proglottids break off and are eliminated with feces and are eliminated with feces

CLASS CESTODACLASS CESTODA