Polyps, Jelly -fishes and Sponges. 67 



in the tentacles not being retractile. The colour is normally 

 ohve green, with the tentacles beautifully tipped with \dolet ; 

 a variety also occurs in which the animal is of a uniform slate- 

 grey tint. The Wartlet, Tealia crassicornis (Fig. 81) has a much 

 tougher body, covered with wart-like tubercles, and variegated in 

 colour, bright red and green ; the short retractile tentacles are red, 

 banded with pink. This species is usually found on sand or 

 gravel at the bottom of pools, where it often lies half buried and 

 concealed by adherent sand-grains or shell fragments. The 

 most beautiful, as well as the largest, of the British forms is 

 +he Plumose Anemone, Actinoloha dianihus (Fig. 80), the sea-pink 

 5ee-Nelke) of the German naturalists, and a great favourite 

 n salt-water aquaria. It frequents rather deeper water than 

 the species we have just mentioned, but is sometimes found on 

 rocks or attached to the wooden piles of piers at extreme low 

 tide. The pale yellow or pink body reaches a length of six inches ; 

 tiie oral extremity is deeply lobed, each lobe bearing a multi- 

 tude of small tentacles. 



A number of common sea-anemones are remarkable on 

 account of their constant association \vith other marine animals ; 

 for instance, Sagariia parasitica is always found attached, 

 either singly or in small groups, to a whelk-shell inhabited by 

 the hermit crab {Eupagums bernhardus). The advantages of 

 such an association are pretty obvious ; the crustacean is con- 

 cealed by the polyp and also protected by means of its stinging 

 cells, while the anemone benefits by the increased aeration of 

 its tissues, due to change of position, and also obtains its food 

 largely from the debris of the hermit crab's meals. The term 

 commensahsm is used to denote such associations leading to 

 mutual advantage. More than two different animals maj' be 

 concerned in this partnership ; thus, in the case just mentioned, 

 the hermit crab, m addition to carrying commensal anemones, 

 frequently shelters a bristle-worm (Nereis fucata), which lives 

 m the uppermost whorls of the whelk-shell, and is only visible 

 at meal-times, when its anterior extremity may be seen pro- 

 truding from the mouth of the sheU in readiness to seize its 

 share of the food roughly torn up by the pincers of the crustacean. 

 Adamsta palliata is another species of anemone commensal of 

 a smaUer hermit crab {Eupagums prideauxi). In this case the 

 association is even more intimate, for the body of the anemone, 

 instead of being cyhndrical, is spread out like a cloak, closely 

 covering the shell, and the mouth and tentacles are situated 

 on the lower surface in close proximity to the mouth parts 

 of the crab, m the best possible position for securing 



