Where is the squid shell found and what is it called

It is called pen and it is located at the dorsal side

Explanation:

Squid belongs to the class Cephalopoda, subclass Coleoidea which is characterized by internal shell (unlike subclass Nautiloidea in which shell is located externally).

The shell of the squid (the pen) in very reduced and small, formed from chitin and located at the dorsal side. The pen provides attachment for muscles and it gives the squid stiffness.

Most likely, this internal shell evolved from the  external shell, because it is believed the ancestral of the organisms from the Coleoidea was probably nautiloid-like.

1) gene flow

- it is described as the transfer of genes from one population to another population so that frequency of gene is increased.

-a zebra migrates to join a different herd of zebras.

2) natural selection

- a mechanism of evolutionary change in which individuals with advantageous traits survive and reproduce whereas the others ( those that can not adapt) eliminate from the population.

-competition for sunlight leads to taller trees.

3) mutation

- permanent change in the nucleotide sequence of dna ( genetic material) that could have harmful or useful consequences.

-the dna of a snake changes to make its venom stronger.

4) genetic drift - it is a random phenomenon ( that occurs by chance such as fire) that results in change in the gene frequency in a small population.    

-a grassfire randomly sweeps through a population of buffalo and kills most of the animals.

explanation:

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.