Fig. 2. Transporters and enzymes putatively involved in the process of ammonia excretion in crabs. Note: composition and localization of transporters may vary between crab species. (1) Na⁺/K⁺-ATPase; (2) K⁺ channels; (3) Na⁺/K⁺/2Cl^– co-transporter; (4) Na⁺/H⁺ exchanger; (5) HCO₃^–/Cl^– exchanger; (6) V-type H⁺-ATPase; (7) Carbonic anhydrase (CA); (8) amiloride-sensitive cation-permeable channel-like structures of the cuticle; (9) Rhesus-like protein (RhCM), putative ammonium transporter with unknown localization. For further information please refer to Table 2.