Algae produce numerous biologically active substances, some of which could be turned into brand-new medications. Thus, the current work utilized Biomphalaria alexandrina snails as a biological model to assess the anesthetic effect of Cladophora glomerata methanolic extract. After 24 h of exposure followed by 24 h as a recovery period, the results indicated that C. glomerata extract was safe for snails up to 500 mg/L. The anesthetic effect was seen with snails subjected to 500 mg/l, reaching 100%, while the relaxation effect was observed with snails subjected to 100 and 300 mg/ L, recording 13.3 and 66.6% of the exposed snails, respectively. The total hemocyte count was directly proportional to the concentrations of algal extract after 1 h, however, it returned to normal after 20 h. Exposure of snails to different concentrations of the algal extract led to several rapid changes in the shape and content of hemocytes and stimulated hemocyte division after one hour of exposure. Acetylcholinesterase activity (AChE) and Lactate dehydrogenase (LDH) levels significantly decreased in all treated snails. GC-MS results exhibited that C. glomerata extract contained 16 chemical substances, which might possess anesthetic, antioxidant, and anti-inflammatory activities and stimulate cell proliferation.