Theory:

Phylum: Porifera
Cell structure: Multicellular
 
sponges.jpg
 
Characteristics:
  • Multicellular, sponge-like, marine organisms.
  • Have pores in the body called Ostia.
  • Found inside the marine ecosystem.
  • Water enters inside the pores and circulates in the canal like system.
  • Receives food and oxygen through the water that enters the pores.
  • Reproduce sexually and asexually.
Example:
Euplectella sycon. Calcarea (Calcareous sponges)
Phylum: Coelenterata
Cell structure: Multicellular
Symmetry: Radial
Germ layer: Diploblastic (ectoderm & endoderm)
 
jelly fish.jpg
  
Characteristics:
  • A jelly type substance called mesoglea is found in between ectoderm and endoderm.
  • Animals in this phylum have a central gastrovascular cavity known as coelenteron with a mouth. The mouth is surrounded by short tentacles which can have cnidoblast or nematocyst which bear stinging cells.
  • Coelenterates has a peculiar character of polymorphism. Accordingly, the same individual exhibit characters of two different types of individuals.
    Reproduce sexually and asexually.
Example:
Hydra, Jellyfish
Phylum: Platyhelminthes
Cell structure: Multicellular
Symmetry: Bilateral
Germ layer: Triploblastic
 
tapeworm.jpg
 
Characteristics:
  • Animals belong to this phylum are parasitic.
  • These animals have hooks and suckers that help them to attach to the host.
  • Special cells called flame cells help the animals to excrete.
  • Reproduce sexually. These animals are hermaphrodites have both male and female reproductive organs in the same individual.
Example:
Flatworms like Liverfluke, Tapeworm
Phylum: Aschelminthes
Cell structure: Multicellular
Symmetry: Bilateral
Germ layer: Triploblastic
Coelom: Pseudocoelom.
 
round worm.jpg
 
Characteristics:
  • Parasitic animals.
  • Round bodied animals without segments.
  • Covered by a thin cuticle.
  • Separate sexes are found in this category of animals.
  • They spread diseases like elephantiasis and ascariasis.
Example:
Roundworms like Ascaris and Wuchereia
Reference:
Image credit:
Sponges: Free image from Wikipedia; https://commons.wikimedia.org/wiki/File:A_Guantanamo_sponge_-a.jpg
Jellyfish: Free image from Wikiwand; https://commons.wikimedia.org/wiki/File:A_Guantanamo_sponge_-a.jpg
Tapeworm: Free image from Wikipedia;https://upload.wikimedia.org/wikipedia/commons/5/54/New_Zealand_flatworm.jpg
Roundworm: Free image from Wikipedia; https://en.wikipedia.org/wiki/Nematode#/media/File:Soybean_cyst_nematode_and_egg_SEM.jpg