Sensory Organs  

Eye stalk and Eyes

The Solider crab has two compound eye which are found at the apex of eyestalks.

One of the most important neurosecretory systems in the decapod crustacenas is the eyestalks(Ruppert et al. 2004). Similar to families Ocypodidaea and Gonplacidae, Mictyridae (the family solider crabs belong to) has narrow fronted, vertically long, close together eye stalks which are raised well above the carapace. This is more unusual in the Braychurans compared to the broad fronted, far, short eye stalks of many of the other families. The eye stalk can rotate around three axes and can be withdrawn into grooves along the carapace, if a threat is perceived (Zeil et al. 1986).

A longer eye stalk, seen in Mictyridae, is a response to the terrain of their environment.  The advantage of long eye stalks, allows partial submergence in water or in sediment while still maintaining perfect vision, this is described as the periscope hypothesis. Another advantage of a long eye stalk is the increase in height above the sediment which increases the area viewable and decreases the effect of surface irregularities on vision, eg. - can still see over a small mound of sand that is the height of their body (Zeil et al. 1986).  The development of this eye stalk and vision system correlates to crabs living in a flat environment (Zeil et al.  1986). The visual streak found in animals that live in open habitats is a horizontal bad across the eye with high retinal ganglion density(Zeal et al. 1986), this is analogous to the acute zone in Brachyurian crabs and is also believed to have evolved in response to a flat environment.