CHARACTERISTIC DEEP-SEA TYPES. 



CRUSTACEA. 



41 



at both ends. To adapt it to its peculiar dwelling, the posterior 

 rings of the tail are formed into a large and bilaterally sym- 

 metrical operculum of calcified plates, which closes the poste- 

 rior opening as effectively as the stout claw does the anterior. 

 The animal is straight, and has not the curved abdomen of the 

 hermit-crabs ; it enters its abode, not backwards, as do the her- 

 mit-crabs, but forwards, head first. Mixtopagurus paradoxus 

 has a slightly asymmetrical tail, in which the rings are more 

 or less distinct, but not completely calcified, so that it is inter- 

 mediate in this respect between Pylocheles and the typical her- 

 mit-crabs. All three of these remarkable forms were taken in 

 100 to 200 fathoms in the West Indian region. 



The species of Catapagurus inhabit depths of 50 to 300 

 fathoms from the southern coast of New England to the West 

 Indies, and live in 

 a great variety of 

 houses which only 

 imperfectly cover the 

 animal, of which 

 the front portion of 

 the carapace is in- 

 durated. They are 

 often associated with 

 a colony of polyps, 

 Epizoanthus (Fig. 

 235), or the house 

 is built up by the 

 base of a simple 

 polyp, Adamsia, which has expanded laterally and united below 

 so as to enclose the crab in a broad cavity. (Fig. 236.) The 

 houses are generally built upon fragments of pteropod shells or 

 worm-tubes as a nucleus. This is frequently resorbed. 



The Epizoanthus houses are very often disproportionately 

 large for the crabs inhabiting them, having grown out on 

 either side until they are several times broader than long. 

 In spite of these enormous houses, both species of the genus 

 probably swim about by means of the ciliated fringes of the 

 ambulatory legs. A similar cooperative association between a 



Fig. 235. Catapagurus Sharreri. 2. (S. I. Smith.) 



