Platyhelminthes

Phylum :platyhelminthes.

Class : Cestoda

example here : tape worm.endoparasite in vertebrate's intestine

Characteristics : bilaterally symmetrical,has a distinct head with scolex to attach to intestinal wall.body usually very longflat and segmented.triploblastic :endo,ecto and mesoderm.

Reproduction :sexual :monoecious/hemaphrodite through proglottids (body segment).sperms fertilise eggs in the proglottids>separated from the worm>pass out in faeces>proglottids degenerate>eggs released(more than a ten thousands)

Pathway towards infecction:the released eggs eaten by animals>enzymes in animal stomach and intestine dissolve egg shell>oncosphere released>enter intestine>hepatic portal vein>liver>Right heart>lungs>left heart>general circulation>muscle where it encyst.>human eat animal meat>enzymes dissolve cyst>adult worms..

Uniqueness :it has more developed nervous system,it has sensory organs(eyespot to detect light)it has head..

so,it is important to cook fish to kill those worms!!

Hydra

Phylum :coelenterata /cnidaria

Class :hydrazoa

Characteristics of cnidarians : radial symmetry and tentacles with stinging cells.

example here :hydra

habitat : clear water,ponds.

Cells : form tissues .cnidocytes : used for defense and capturing prey,with nematocyst in it which has barbs and releases poison to the prey.interstitial cell :gives rise to new cells.

feeding : once prey is captured,is ingested by tentacles into its mouth for digestion in enteron (extracellular digestion) ,undigested food exit through mouth.nerve cells are present too.

reproduction : asexual and sexual. asexual :budding when condition favourable+regenaration .sexual : monoecious with sperm swim towards the ovary for fertilisation.

difference from sponges :One such feature is the presence of a gastrula stage during embryonic development, it has tissues .

porifera

Phylum : Porifera


common name :sponges


habitat:found in marine and fresh water,found sessile( attached to rock or shells)



Cells: are not organised into tissues, but are specialised.


example: porocyte-for entry of water.Choanocyte :food is digested here or passed on to amoebocytes for digestion.food are microscopic organisms .Amoebocyte :mobile and move around the cell body.differentiate to form spicules and carry nutrients to other cells,carry oxygen and waste products.
(http://www.biology.ualberta.ca/courses.hp/zool250/animations/Porifera.swf)

water entry :water enter through pore cell and excreted though osculum.

Reproduction :asexual and sexual.sexual :mostly monoecious where sperm fuses with egg to form zygote.asexual : though gemmule , budding, regeneration.

uniqueness :it is separated in another subkingdom called parazoa because of its distictive characteristic from other animals..