xi WORMS AS HOSTS DISTRIBUTION 299 



the body of the common lug-worm, with the colouring of which 

 it closely harmonises. 



Worms as Hosts. The Polychaeta serve not only as food 

 for fishes, Crustacea, and other predatory animals of larger 

 size, but are also liable to be the hosts of parasites l such as 

 Gregarines, and even, as we have seen, of other members of 

 their own group. Sundry ectoparasitic Copepoda have been 

 found attached to worms between the parapodia or to the sides 

 of the feet, and an unnamed Copepod occurs attached, sometimes 

 in considerable numbers, to the sides of Nereis cultrifera. The 

 Polychaeta also act as protectors to other animals, for on the 

 under surface of elytra of sundry Polynoids may very frequently 

 be found specimens of Loxosoma, which may also be attached to 

 gills of Euriicids ; whilst below those of Aphrodite echidna and 

 Hermadion pellucidum, Pedicellina belgica occurs. Under the 

 felt of A. aculeata the Sabellid Branchiomma vigilans forms its 

 tube, and Vorticellids may be found on chaetae, gills, or other 

 parts of the body of sundry worms. 



Distribution. Very little can be said in a brief way of the 

 geographical distribution of these worms, for many of the genera 

 are cosmopolitan, although only a few species occur in all the 

 great oceans, e.g. Polynoe imbricata, Hyalinoecia tubicola, Nerine 

 (Scolecolepis) cirrata, and Terebellides stroemi. 



As for species, it can be said generally that the different 

 oceanic areas and even different coasts present different species, 

 but we know practically nothing of variation amongst Polychaeta, 

 and many so called species may be mere local varieties, for 

 frequently the descriptions of "new species" are scarcely intel- 

 ligible. At any rate we know that certain species occur at 

 widely separated localities, for two or three species of Polynoids 

 occur in Japan, and again at Dinard on the French coast. A 

 considerable number of species are common to both sides of the 

 North Atlantic ocean, having been obtained off Norway and 

 in the Gulf of the St. Lawrence. A few of these which are 

 common on our coasts may be enumerated : Nereis pelagica, 

 Nicomache lumbricalis, Glycera capitata, Thelepus cincinnatus, 

 Scoloplos armiger, Sabella pavonia, Ophelia limacina, Aphrodite 

 aculeata, Trophonia plumosa, Polynoe squamata, Capitella capi- 

 tata, Sthenelais limicola. 



1 See "Challenger Reports," and St. Josep\ loc. cit. 



