In the atlantic which part of the oceanic crust is younger

Oceanic crust is  younger crust . Well, It is because, an oceanic crust is formed when a continental crust undergoes a big tension crack due to the forces generated inside the earth, which may be because of the magma dwelling inside.  As the crack becomes prominent, the continent is broken into the segments with a big oceanic basin kind of structure between them (This takes millions and millions of years). Sediments deposit in the basin and get stratified to form the oceanic crust.  This is the reason that oceanic crust is younger than the continental crust.

The oldest crust is about 260 million years old. This sounds old but is actually very young compared to the oldest continental rocks.

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.

one is through turgidity. this occurs before ground tissue ( collenchyma

and sclerenchyma cells) become well

developed to give structural support to the plant as it grows bigger. the xylem

tissue (composed of rigid tissue) of the young

plant render this support and also maintaining osmotic turgidity of the surrounding

plant cells.