98 A renicolidae 



sunrise, of specimens (80-120 mm. long) in the smface tow-net, in 

 sliallow water at Heligoland. 



Arcnicola marina is present in certain estuaries in wliicli, especially 

 in times of flood, tlie water is of much less density than sea water. 

 The few records available indicate that Arcnicola adapts itself less 

 readily than Nereis to estuarine conditions — e.g. Ferronniere found, 

 while collecting in the estuary of the Loire, that A. marina ceased at 

 St. Nazaire — i.e. at the mouth of the river, while N. divcrsicolor 

 extended about sixteen kilometres further up the river, to a point 

 well above Paimboeuf. Similarly only one specimen of A. marina 

 was found at Greenlands, three miles up the estuary of the Exe, 

 although iV. (lirersicolor was very common there.^ The water in this 

 estuary is, at certain times, of low density.^ Eecent observations in 

 the Forth show that A. marina extends a considerable distance into 

 estuarine water, and, indeed, occurs in situations — e.g. a quarter of a 

 mile above Kincardine ^ — which are suljject from time to time to 

 submersion in almost fresh water. Above Kincardine the river 

 channel is comparatively narrow ; below that town it opens out into 

 the broad estuary. Specimens living above Kincardine will therefore 

 be submerged in water of low density, and, in times of flood, in 

 practically fresh water. Possibly at those times the worms retire 

 deep into the mud, and thus, perhaps, minimise the effects pioduced 

 by fluctuation in the density of the water. 



Food. — Arcnicola marina feeds on small living organisms, sucli 

 as diatoms, algae, foraminifera, etc., but probably to a greater extent 

 on the small dead animals — Crustacea, worms, etc. — or their frag- 

 ments, which are to be found in the littoral ;cone where Arcnicola 

 marina occurs in greatest abundance. Occasionally a larger object is 

 found in the alimentary tract of the lugwonn — for instance, a piece 

 of seaweed, or a partially digested Nereis. 



' J. Mar. Biol. Ass., n.s., vi, pp. 299, 321. 



- Dr. Miohaelsen {op. cit. (1896), p. 195) thinks that the decrease in the 

 Polychaete fauna, observed on passing from the Sound and the Belt into the 

 Baltic, is probably correlated with the decrease in the salinity of the water. 

 In the Belt there are ninety-six species of Polychaeta, in the western part of the 

 Baltic only forty-three, and in the eastern part, from and including Riigen, only 

 nine, including A. marina. Sassnitz, on Eiigen, is the most easterly locality 

 in the Baltic from which A. marina has been recorded (Mobius). The occur- 

 rence of this worm much further eastwards seems unlikely, for had it been 

 present it would doubtless have been noted in the faunistic lists given for East 

 Prussia. Dr. Alex. Luther, of the University of Helsingfors, has inforn:ied the 

 writer that Arcnicola does not occur in the vicinity of Helsingfors. 



" The author is indebted to Mr. William Evans for this unpublished record. 



