CRAB GENERA PLANES AND PACHYGRAPSUS — CHACE 



75 



• Planes mlnutus 

 o Plones cyaneus 

 + Pachygropsus marinus 



Caropoce Length (mm.) 



Figure 4. — Scatter diagram showing the variation in proportions of the carapace in Planes 

 minutus, Planes cyaneus, and Pachygrapsus viarinus. 



COLOR 



The variable and protective coloration of Planes minutus has been 

 a cause of speculation for more than a century. Some of the early 

 workers believed that those specimens which were greenish or brown- 

 ish yellow mottled with darker shades of the same color sought out 

 Sargassum clumps to live on in order to be less conspicuous to their 

 enemies. These Sargassum inhabitants also often have a large white 

 or yellowish patch on the dorsal surface, which seems to duplicate the 

 patches of bryozoan colonies with which the plant fronds are almost 

 invariably encrusted. Those specimens found on turtles are usually 

 yellowish, those on logs and drifting trees often dark reddish brown, 

 and those on the pelagic gastropod Janthina lilac blue. Light reddish 

 shades have also been recorded on several occasions. Examples of 

 some of these colors are shown in Murray and Hjort (1912, pi. 6). 



Miiller (1881, p. 473) was apparently the first to suggest that these 

 crabs change their color according to the object to which they cling. 



