It's Gaetice depressus (Gd), not Hemigrapsus sanguineus (Hs).
In quick compaison, The carapace of Gd is smooth, flat and has straighter edges. The body form and the legs are more depressed (in comparison to Hs) which are typical appearance of a Varunid crab (Gd belongs to the family Varunidae) such as Varuna littorata. The tips of the claws are more pointed (in comparison to Hs) and usually pale white in colour. The 3rd maxillipeds (or put it simply, the mouth) are broader and more setose (or more "feathery") which is well-adapted to its filter-feeding habits.
In contrast, the carapace of Hs is round & smooth and the body is less depressed in comparison to Gd. The hairs on the legs of Hs are stiffer and the tips of the legs (the dactyl) are more adapted to clinging on surfaces (like a hook). The claws are mottled with small dark spots, often appear purplish at the front portion, and the tips are blunt, depressed (which looks like a spoon) and equipped with sensory hairs which is typical to the herbivorous shore crabs. All these are typical features of Grapsid crabs such as the common shore crab Grapsus albolineatus. Also, you can see a watery vescicle at the base of the claw digits, which is a distinguishing feature of Hs. The 3rd maxillipeds are smaller and less setose as compared to Gd. When viewing from the front, you may notice a prominant white ridge running through the pterygostomial region (the "cheek"), which is less prominant in Gd.
Hope this is of help.
[ 本帖最後由 DecaPoda 於 2015-2-3 19:10 編輯 ]
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