Flatworm get most of their oxygen through diffusion.
The answer is a simple radial nervous system.
Echinoderms do not have brains. Around their mouth, they have central rings from which nerves radially run into arms and along the body. Movement is controlled by the branches of those radial nerves.
B. They are determined by I, AB, A, or B
Answer: crossing over happens in prophase 1.
Explanation: ( in Portuguese ) os cromossomas homólogos, na profase 1 da meiose, tocam-se, trocando informações sobre o ADN. A esse processo chama se crossing over.
