Phylum Platyhelminthes (Zoo Exam 2)

after Xenacoelomorpha

____ begin with Platyhelminthes

Protostomes

All have mesoderm but no ______

coelom

Free living form have ____

ciliated epidermis with rhabdites

What do rhabdites do?

Secrete mucus to move and cilia beat within the mucus layer to propel the worm

Parasitic are ______

nonciliated syncytial insunk cells

Syncytial =

no membrane between cells

Larval ____ initially have ciliated epidermis which is shed upon entering the host

parasites

Parasitic worms need an epidermis that is:

• strong enough to withstand hosts digestive enzymes

• thin enough to absorb host’s nutrients

• evade host’s immune system

_______ below the epidermal basement membrane

muscle layers

______ fill in the space between syncytial surface and cell bodies of the epidermal cells

Parenchyma cells

Gut in general:

Have mouth, pharynx, and intestine - no anus

_____ has a columnar epithelium with cells secreting digestive enzyme into gut, then cells take in digestion food via phagocytosis

Intestine

For secretion and osmoregulation:

use flame or protonephridia flagella beat and create (-) pressure in cage to

• draw fluids into cage area

• and send them into the tubule

• tubules —> collecting ducts —> open to outside via nephridiopores

• cells in the tubules absorb needed ions

• some metabolites, what is not needed remains in tubules and exits nephridiopore

Nervous system may include:

brain, paired nerve cords, transverse nerves

Brains collects sensory information -

ocelli for light, chemo receptors for detecting chemicals (like prey) and touch detecting mechanoreceptors

Many parasitic types have an _____ stage where they reproduce

asexual (may be by fission)

Sexual reproduction are _____

Monoecious

• yolky eggs with an eggshell

• internal fertilization

Internal fertilization:

• have a uterus for brooding zygote

• males include testis, vas deferens penis

• may use a female vagina to add sperm

• or just stab anywhere on the partner’s body

Class Turbellaria is ____

free-living

Class Turbellaria gut is

simple or branched, no anus

Class Turbellaria locomotion

via cilia, mucus, muscular contractions

Feeding in Planaria

• carnivorous, sniff out prey

• entangled prey in mucus

• anterior (head) end wraps around prey

• mouth is ventral (underside)

• pharynx extend into prey to digest it

Class Trematoda is ____

Parasitic and includes liver fluke

Class Trematoda external body plan:

• Externally have 2 suckers to attach to host intestine - oral sucker and anal sucker

Class Trematoda internal body plan:

• Internally - pharynx, esophagus, branched intestine

• reproduction system takes up 80% of body

Class Trematoda feeding:

• gut is simple: sucker —> esophagus —> intestinal cecae

• graze on host cells and body fluids

Class Trematoda reproduction:

Monoecious

Class Trematoda Life Cycle

• eggs shed into water

• make their way into a snail

• larvae develop, reproduce asexually in snail

  • which exit snail, locate next host, a fish

  • burrow under fish’s scales, make cysts in the muscle

  • if a vertebrate host eats fish with cysts, will start cycle again

Class Monogenea

• Also fluke parasites in fish gills, frog/turtle bladders, and hippo eyeballs

• posterior attachment is a set of hooks

Class Cestoda

tapeworm

Class Cestoda scolex:

On posterior end attaches to intestinal wall via hooks and suckers

Class Cestoda body surface:

Covered with microvilli to increase surface area for absorption

Class Cestoda ___ gut and ___ head

no

Class Cestoda reproduction:

• proglottids (a long chain of reproductive units) develop gonads, oldest at free end

• fertilize with neighbor proglottid or by folding on itself (sperm exchange)

• embryos in proglottid uterus

• release eggs/embryos (eggs contain embryos) through genital pore

• proglottids can be released too

• if on grass, cattle or other grazer can eat them, encyst in host’s muscle

• humans eat undercooked “measley meat” and gets infected

Platyhelminthes are grouped as members of the _____

Lophotrochozoa