This guide is designed for identification “in the field” where you might be looking at live crabs by eye or through binoculars or from photographs. I will generally try to avoid characters that will require you to physically catch the crab, although I may mention a few for secondary verification. It does not include the more strict taxonomist-style characters that may only be visible under a microscope or via dissection. It is also assumed that the individuals are living, as death (and even capture) can cause dramatic color change.
This is a guide to the fiddler crabs of the northern Persian Gulf and nothern Gulf of Oman, including Kuwait, Iraq, and Iran. There are only two species found over most of this coastline, with a third only present on the island of Qeshm.
Austruca sindensis is easy to identify by color. Its carapace is generally pale gray, with darker stripes, and its large claw is predominantly lilac.
Austruca iranica is easily distinguishable from Austruca sindensis. It has a carapace that is usually solid white (occasionally with a mix of white and gray/black), its limbs range from dark red to white, and the large arm and claw are usually white (sometimes with a bit of subtle pale color).
Within the nothern Persian Gulf, Cranuca inversa is only found on the island of Qeshm, Iran.
Male Cranuca inversa are easy to identify, provided one gets a good look at the large claw. In this species, the tip of the dactyl (the upper finger) on the large claw has a forked shape which is completely unique to this species. Compare the forked tip in the photos below to the tip of the large claw of the other species shown on this page.
The “hand” and arm of the large claw tend to be pale pink, while the fingers are usually white. The carapace is generally a mix of black and white, usually—although not always—with more black than white. Unfortunately, this color scheme can be similar to Austruca iranica, so without a good view of the tip of the large dactyl, it may be difficult to distinguish between them in the field. Austruca iranica are usually mostly white and Cranuca inversa are rarely so, but there is some overlap between the two.