MARINE WORMS. 35 



the sand scooped up as Spatangus feeds, harbours many other 

 tiny animals, for which, no doubt, Polynoe castanea keeps a 

 keen look-out. 



Quite a common habit of many of the Amphipods and 

 other minute crustaceans is to take advantage of dark nooks 

 and corners as temporary lurking places, such for instance as 

 the open ends of large worm-tubes, and hence several Polynoes 

 have found it advantageous to take up life-long abode with 

 the owners and builders of such tubes. Two — Polynoe seto- 

 sissima and Nychia cirrosa — have selected as their host that 

 most curious of our local tube-building worms — the ungainly 

 Chcetopterus. The tubes of this last mentioned worm are not 

 uncommon in the dredge off Herm, and on the shore there at 

 extreme low water the two projecting ends of their tubes- -they 

 construct U-shaped ones — are often to be seen. If we dig up 

 an inhabited one and tear it open, one or other of the two 

 species of Polynoe I have mentioned is sure to be found. Both 

 are large, among the largest of our local species, and P. setc- 

 sissima is perhaps the most elegant of the family ; the bundles 

 of pale golden bristles arming its many feet are stout and long 

 and projecting like so many grouped and serried banks of gilded 

 oars, and recall to one's mind those wonderfully-dight state 

 barges rowed by a myriad oarsmen in which the Doge of Venice 

 of old used to wed his glorious city to the beneficent Adriatic. 



Another tube-worm, Terebella nebulosa, sometimes gives 

 hospitality to Polynoe johnstoni, Marenzeller (P. scolopendrina 

 of previous British writers), a much elongated species, which 

 on account of this very length of body is dependent to a great 

 extent upon the protection of a host's tube. The only two 

 Polynoes of great length which I have met with in British 

 seas are the present P.johnstoni and the equally long Acholoe 

 astericola. The latter is much more thoroughly commensal 

 than the former, its only known habitat in our seas being as 

 guest of the pretty starfish Astropecten aurantiacus, where it 

 lies stretched along one of the ambulacral grooves. 



It is appropriate to mention here that such of the Polynoes 

 as are unmistakably free and non-commensal are all of short 

 length. It is obvious, other things being equal, that the 

 longer the body the greater must be the danger of capture, 

 and the inference is that without some device for gaining arti- 

 ficial protection, the long forms would soon cease existence 

 under the grinding competition for life ever waging among 

 animals. As proof that shortness of body is of the highest 

 value to free-living Polynoes^ we have to note that the 

 commonest and characteristic free species of the district, 



