Key to the species of Macrophthalmus in the Persian Gulf and the Gulf of Oman

1. Distinct chitinous plectrum near lower margin of inner surface of merus of male cheliped........................... 2

- Without plectrum on the upper surface of merus of male cheliped............................................... 3

2. Eyestalks stout, hardly reaching exorbital angle; lower orbital margin with small rounded tubercles; palm with longitudinal ridge on outer surface, inner surface fully covered with dense setae; small-size species (CL <10 mm); occurring on rocky shores.................................................................................... M. sinuspersici

- Eyestalks narrow, not reaching to exorbital angle; lower orbital margin with long tubercles; palm without longitudinal ridge on outer surface, inner surface only with a longitudinal row of setae on upper potion; large-size species; occurring on muddy substrates....................................................................................... M. dentipes

3. Eyestalks projecting beyond tip of exorbital angle........................................................... 4

- Eyestalks never projecting beyond tip of exorbital angle...................................................... 6

4. Eyestalks extremely long, extending beyond exorbital angle for half of its length; second anterolateral teeth of carapace nearly as long as exorbital angle....................................................................... M. serenei

- Eyestalks not extremely long, extending only slightly beyond exorbital angle...................................... 5

5. Apical portion of cornea with unique extension, about half of the cornea extending beyond exorbital angle; exorbital angle longer than second lateral tooth of carapace; inner surface of palm of male cheliped without spine on proximal portion, without patch of setae................................................................................ M. graeffei

- Apical portion of cornea without extension, extending beyond exorbital angle; second lateral tooth of carapace larger than exorbital angle; inner surface of palm of male cheliped with spines on proximal portion, patch of dense setae covering most part of inner surface, immovable finger strongly deflected............................................. M. sulcatus

6. Exorbital angle much smaller than second lateral tooth of carapace; palm with longitudinal ridge on outer surface, inner surface of palm with spines on proximal portion.................................................... M. grandidieri

- Exorbital angle not larger than second lateral tooth of carapace; eyestalks never reaching tip of exorbital angle............ 7

7. Walking legs with dense setae; palm of male cheliped with inner surface fully covered with dense setae, without spines on proximal portion............................................................................ M. depressus

- Walking legs without [dense] setae; palm of male cheliped without setae on inner surface; spines on proximal portion of inner surface of male cheliped......................................................................... M. laevis