The imperial shrimp, Periclimenes imperator, is sometimes seen riding on the back of large sea cucumbers. The shrimp gets to move around to areas with food and expend very little energy, while the sea cucumber is unaffected. What type of relationship is this, and why?

A. Commensalism, because one species benefits
B. Mutualism, because both species benefit
C. Parasitism, because one species is harmed
D. Predation, because one species dies

endo:

regulates body hormones, aldosterone, vasopressin

neural:

signal, regulates body using electric signals, reflex

endo has to do with hormones; aldosterone and vasopressin are both hormones. i also had this question and got it right : d

not necessarily. higher fitness requires the organism to be reproductive successful. for example, an organism at age 10 with 15 offspring is much more fit than an organism at age 15 with only 5 offspring.