Hapalocarcinus, the Gall-forming Crab, etc. 61 



CRYPTOCHIRUS HELLER. 



Cryptochirus is a genus described by Heller in 1872 from the Red 

 Sea and associated by Caiman with Hapalocarcinus to form the family 

 Hapalocarcinidae. Heller was not able to impart much information 

 about the biology of the crab, but he gives an accurate account of the 

 structure, even to the minute oral appendages, accompanied by figures 

 which are helpful if hardly adequate according to present standards. 



Semper was the first to supply first-hand observations of the living 

 animal which he found inhabiting various Astraeid corals in the Philip- 

 pines. He discusses the interaction of crab and coral polyps in a 

 passage which I will quote in full. 



Semper first states that the influence of the respiratory current of 

 Cryptochirus is exerted in quite a different way to that of Hapalocar- 

 cinus. This is due to the fact that the former genus only inhabits 

 the more massive forms of coral and consequently the cavities in which 

 it lives are unlike those in which Hapalocarcinus is found: 



"Here there are no galls, but merely cylindrical or funnel-shaped hollows, 

 which are never closed during the lifetime of the crab, so that it certainly 

 would be able to quit its position. Nevertheless, it as certainly does not do 

 so; but the species I observed living thrust the forepart of their bodies very 

 far out of their peculiar 'cave dwellings,' so that only their pouches, i. e., the 

 hind part of the body, remained within. The cavity itself exhibits some 

 remarkable peculiarities. The bottom of it, on which the pouch rests when 

 the creature has completely withdrawn itself into it, displays the radial septa 

 of a polyp-cup one above another. They there are perfectly distinct, while the 

 side walls of the cylindrical cavity are so completely lined with a thin cal- 

 careous crust that nothing can be seen of the perpendicular septa of the polyp- 

 cup. From this it is evident that the young crab, or the larva of it, takes up 

 its abode in the centre of a cup, and so kills the polyp inhabiting it. A speci- 

 men now lying before me, with an incomplete cave-dwelling, shows that the 

 crab grows at first at the same rate as the surrounding polyps; for the margin of 

 the crab's hole, which is perfectly cylindrical, is on exactly the same level as 

 the neighbouring cups, and its breadth too is exactly the same. The cavity 

 is six millimetres long, and the length of the crab found in it exactly corre- 

 sponds. In another example, however, the length of the pit is twenty milli- 

 metres, while that of the crab belonging to it is not more than seven milli- 

 metres, at any rate in the dried state. This proves that the crab ceases to 

 grow much sooner than the coral; and this conclusion is strikingly confirmed 

 by the fact that the margin of the cylindrical pit is not on the same level as 

 that of the surrounding polyp-cups, but much deeper. From the margin of 

 the crab's dwelling, properly so called, there is a funnel that widens to the top, 

 and of which the margin, as is shown in the cut (fig. 68), is gradually merged 

 in the upper prominences of the coral. The crab living in the funnel thus 

 formed was carefully observed by me during a long period of its life, and I was 

 enabled to see that it protruded itself far enough out of its hole to be able to 

 reach with its outstretched fore-claws almost to the highest portion of the 

 funnel. 



"The whole conditions here described allow of no other explanation than 

 the following: At first the crab and the coral grow at an equal rate; for, if the 



