Cephalopods have a closed circulatory system where blood is transported through vessels. However, most other mollusks have an open circulatory system where blood is not always in vessels, but is spread over the organs.
Sand or minerals but i think it could be minerals
The proteins that bind to signaling<span> molecules and initiate a physiological response are also referred to as receptors.
</span>Cell-to-cell communication relies upon the adhesive molecules integrins. Integrins allow cells to maintain contact with one another.<span> Integrins are mechanical links and relay signals both to and from cells.</span>
The question is unclear, is there more to it?
I cannot answer this question without knowing the circumstances, but it is good to remember that mutualism is where both species and/or participants benefit, and parasitism is where one species benefits and the other one is harmed.
Think of mutualism like the word mutual, so when people say " the feeling is mutual" it means that both parties feel and/or express the same feelings. Parasitism should be thought of like a parasite. When one is infected or has contracted a parasite, the parasite will live off of its host body making it ill or even causing death as it drains resources from its host to benefit itself.
