Aplysia californica , or the California sea hare, is an important animal in the scientific community. Neurological studies have put Aplysia in the spotlight, however, there is little to no research on the immune system of these animals. There is proof of neural-immune linkage in this animal, so investigation further into the immune cells of this animal is of interest. In my study, I use histological methods to characterize the composition of the hemocytes (blood cells), and speculate as to how many cell types there are along with their function in the immune system. Preliminary results show presence of carbohydrates (such as glycogen), lysosomes, mitotic activity in circulation, and overall structure of the cells. Secondly, I attempt to assess temperature stress in Aplysia by placing specimens in temperature-controlled rooms. Total hemocyte count (THC) was calculated and glucose levels were measured in each temperature over a period of 1 week. Results of this experiment are variable, and I need further analysis and better experimental set-up to make a definitive statement. Third, I followed the development of Aplysia veligers (larvae) and recorded the process in photographs for approximately 25 days.