182 



ASSOCIATION OF ORGANISMS THE WEB OF LIFE 



of the Andaman Islands, and in this case the messmate is cap- 

 shaped, and fits very neatly to the back of its active partner. 



Hermit-Crabs are also in some in- 

 stances associated with sponges, one of 

 them (Eupagurus Cuanensis) being par- 

 ticularly notable in this respect, for the 

 shell in which it lives is completely over- 

 grown by an orange -coloured species 

 (Suberites domun.culus\ leaving only a 

 small aperture to serve as a front door. 

 As this particular sponge is not only full 

 of sharp spicules, but also disagreeable 



to both sme11 and taste > we mi s ht ex - 



pect it to prove a very efficient protec- 



tion, and Garstang has found by actual experiment that fishes 

 find it extremely repulsive. 



Fig. n 3 o.-under view of an Andaman 



SIPHON-WORMS (GEPHYREA) AS MESSMATES 



Some of these curious worms take up their quarters in 

 empty shells, and in certain cases this has led to a curious kind 

 of commensalism, to some extent reminiscent of what happens 

 in hermit-crabs. For just as anemones attach themselves to the 



dwellings of hermits, so do 

 certain simple corals affix 

 themselves to the shells appro- 

 priated by siphon-worms, after- 

 wards increasing in size so as 

 to conceal these from view, so 

 that in the end we find the 

 base of the coral traversed 

 by a kind of tunnel serving 

 as the home of the worm (fig. 1131). Three different species of 

 coral (Heteropsammia Michelini, Heterocyathus czquicostatus, and 

 Stephanoseris Rousseaui) have been described from the Indian 

 Ocean, each living with a distinct species of a kind of siphon-worm 

 {A spido siphon). Shipley has carefully examined the species \A . 

 corallicola) associated with the first-named coral, and makes the 

 following interesting remarks about the partnership (in Ceylon 

 Pearl Fishery Report\. "The whole question of such com- 



Fig. 1131. Under (left) and Upper (right) Sides of a 

 Cup-Coral (Heteropsammia Michelini}, snowing opening 

 of the dwelling of its Commensal Siphon-Worm (Aspido- 

 siphon corallicola) 



