64 Papers from the Department of Marine Biology. 



A COMPARISON OF HAPALOCARCINUS AND CRYPTOCHIRUS. 



There is no doubt that Hapalocarcinus and Cryptochirus are very 

 closely related. The same striking modifications of structure occur in 

 both. Of these the reduction of the oral appendages and the gastric 

 mill show a common method of feeding, while the abnormal growth of 

 the abdomen is connected with the production of large broods of eggs, 

 a property very necessary for a sedentary animal. The structure of 

 the oral appendages and the maxillipeds is almost identical in the two 

 cases (text-figure 16). The abdominal appendages, also, have exactly 

 the same modifications. 



ex. nip. 2 



FIG. 16. Buccal area of Cryptochirus. X 90. 



For comparison with that of Hapalocarcinus. Drawn from a specimen cleared in potash and 

 mounted in Canada balsam. On one side maxilliped 3 and parts of other appendages have 

 been removed; on the other maxillipeds 1 and 2 are shown occurring beneath 3. The pa- 

 pillae on the surface of maxilliped 3 are indicated by small circles. It will be seen that max- 

 illiped 3 comes much closer to the middle line than in Hapalocarcinus and that the provision 

 of setse for the exopodites of maxillipeds 1 and 2 is not marked, while they are not found on 

 the border of maxilliped 3. The main work of sieving is done by the strong setae arising from 

 the endopodites of maxillipeds 2 and 3. The sieve has not so fine a mesh as in Hapalocarcinus. 



B. mp. 1, C. mp. 2, basipodite and coxopodite of first maxilliped; mx. 1, mx. 2, first and second 

 maxillae. Other letters as in text-figure 5. 



Such structural differences as exist correspond to their diverse 

 habitations. Hapalocarcinus affects branching corals with individual 

 polyps much smaller than itself, even at the earliest stage, and forms a 

 complicated gall almost completely shut off from the exterior by con- 

 trolling and modifying the branching of the coral. Cryptochirus, on 

 the other hand, seeks to house itself in massive Astraid corals, where 

 the individual thecse are of such size as to accommodate the intruder. 

 It occupies a theca after passing through its larval stages and very soon 

 the growth of the polyp is suppressed and death will follow. The 



