Midterm 1 - platyhelminthes and lophotrocozoans

4 major features of bilateria

1. bilateral symmetry

2. cephalization (sensory organs and nerve tissue all at anterior end)

3. triploblastic (ectoderm, mesoderm, endoderm)

4. hox genes

how is protostomia characterized

mouth forms before anus during embryonic development

how is deuterostomia characterized

anus forms before mouth during embryonic development

which 2 subclades, and their phylums, are found within protostomia

1. lophotrocozoa: mollusca, platyhelminthes, rotifera, nemertea, annelida

2. ecdysozoa: arthropoda, nemotoda

what is a lophophore

a specialized ring covered in ciliated tentacles that some lophotrocozoans develop, used to filter food

what is a trocophore

a larval stage that some lophotrochozoans have

name and describe the 3 body plans

1. Acoelomate: lack a true body cavity. the gut and body wall is filled with mesodermal tissue

2. Pseudocoelomate: possess a false body cavity that is fluid filled, partially lined with mesoderm

3. Eucoelomate: have a true body cavity completely lined with mesodermal tissue

   

how do coeloms form in protostomes

process called schizocoely: mesoderm forms solid masses that split internally

how do coeloms form in deuterostomes

process called entercoelly: pouches bud off from archenteron forming mesodermal cavities

describe the major characteristics of platyhelminthes

• acoelomate

• unsegmented

• have organs

• have a gut with one opening (no anus)

• flattened

• have cilia for movement

• have nervous system with cerebral ganglia and nerve cords

• have photonephridia

• triploblastic

two features of platyhelminthes nervous system

1. cerebral ganglia (bi lobed brain)

2. have 2 nerve cords

photonephridia function

excretory organ that used for osmoregulation and excretion of ammonia

what are flame cells

specialized excretory cells found at the ends of photonephridias branches. they have beating cilia that draw fluid into tubules, useful materials are reabsorbed and waste is released through nephridopore

how do they capture food

they are predators or scavengers. pharynx extends mouth towards prey, then secretes digestive enzymes

what are neoblasts

adult stem cells that allow continuous repair and regeneration

how do they asexually reproduce

binary transverse fission: organisms divide into 2 halves along horizontal axis, neoblasts form a blastema at site of fission, regenerates into 2 daughter organisms

describe the 3 ways that they sexually reproduce

1. internal fertilization: they are hermaphroditic so can fertilize themself

2. cross fertilization: between two seperate worms or 2 proglottids on one worm

3. bilateral sperm transfer: (method of cross fertilization) both partners exchange sperm and fertilize each other

what are the 4 major platyhelminthes classes

1. turbellaria (planarians)

2. trematoda (flukes)

3. cestoda (tapeworms)

4. monogenea (ectoparasites of fish)

class turbellaria

planarians. free living freshwater, marine, or terrestrial flatworms, not parasitic

class trematoda

flukes. endoparasites, have suckers and hooks

class cestoda

tapeworms. endoparasites, have scolex with hooks and suckers, and proglottids

class monogenea

ectoparasites of fish. spend their whole life attached to fish, ciliated eggs hatch and either attach to fish or free swim until new host

fluke life cycle key terms

• miracidium: ciliated larva hatched from egg.

• sporocyst: miracidium transform into sporocyst inside snail

• redia: sporocyst transform into redia inside snail

• cercariae: motile larva released from snail

• metacercariae: inside fish

tapeworm (cestoda) life cycle

• proglottids contain eggs that break off and pass through hosts poo

• animal (intermediate host) eat contaminated grass or water

• eggs hatch into larvae inside host

• larave form protective cyst in animal muscle

• humans eat animal, scolex attaches to intestine