Adaptations in Structure and Habits of Certain Marine Animals. 59 



I studied the habits of these animals as well as I could in dim hght 

 in the cavities of pieces cut from the sponge. They appeared to behave 

 normaUy, whereas in glass tubes in brighter hght they remained motion- 

 less. Both animals explore the cavities of the sponge with cautious 

 movements unless disturbed, in which case they snap their claws. The 

 Alpheid advances, using its large claw as an antenna and protector. 

 Its antennae can be extended about as far forward as the large claw. 

 When meeting an Alpheid or a Pontoniid it may try to squeeze past or 

 it may snap its claw. When placed in glass dishes Alpheids cut one 

 another to pieces, but this is seldom if ever done in the narrow passages 

 of the sponge. 



The Pontoniid Typton tortugcB advances, using both claws as an- 

 tennae, the antennae being very much shorter than the smaller claw. It 

 spreads the claws apart and waves them about, thus exploring the cavity 

 in front of it. On meeting another it behaves as the Alpheid, except that 

 it may snap either or both claws. Both animals try to squeeze through 

 small openings. The chelae of Typton sometimes show what appear 

 to be claw marks. As their claws are more slender, hence more easily 

 grasped and less powerful than those of the Alpheids, it is to be expected 

 that they would show claw marks first in case both species snapped with 

 equal frequency. 



Both animals appeared to eat from the walls of the cavities in the 

 sponge, but I did not determine whether they ate the sponge itself or a 

 sediment deposited on it. I did not determine whether they ate one 

 another in the sponge, but they were so numerous that it seems strange 

 that they received sufhcient oxygen. The Alpheids are sometimes in- 

 fested with a parasitic isopod, Bopyrus, in the gill cavity. 



I do not intend to discuss here the origin of the form or habits of 

 these animals, but it seems to me that we have here a convergence both 

 in form and habit. It is probable that similarity in form and habits 

 made both animals better suited to Hving in the same habitat, i.e., the 

 sponge, and that accidentally finding the sponge they remained there. 

 However, this does not explain why the young at the end of pelagic hfe 

 alwavs (or at least usually) select the loggerhead sponge. There are 

 numerous Alpheids living in holes in the reef rocks, and certainly they 

 are more closely related in form and general habits to Synalpheus brooksi 

 than is Typton. 



This Synalpheus and the Typton select the sponge not because it 

 has holes in it in which they can hide, but on account of some more 

 specific quaHty, such as taste (smell), color, or outward form. Or when 

 some individuals of these species have estabHshed themselves in a sponge 

 the others may be attracted to it by a social instinct (which may not be 

 disproved by the fact that they destroy one another when placed under 

 unnatural conditions). The isolation of these animals in the loggerhead 

 sponge is an example of what GuUck calls habitudinal segregation and 

 may have been a factor in the evolution of the species. 



Since the Alpheids occur in far greater numbers than Typton we 

 might suppose the former to be much better adapted to living in the 

 sponge than the latter. However, although Typton produces more 



