326 



POLYCHAETA 



Cirratulus. The prostomium is long, sometimes annulated. 



In addition to the segrnental filamentous " gills " there is a 

 transverse row of long " tentacular fila- 

 ments " across one of the anterior seg- 

 ments, and it has been suggested that 

 they are really prostomial tentacles 

 which have shifted backwards. They 

 and the gills twist about in a very 

 active fashion during life, and look 

 like small independent worms, especially 

 when they are detached. C. cirratus 

 Mull, is a brown or dirty yellowish 

 worm about 4 to 6 inches in length, 

 usually to be found under stones, 

 partially embedded in the mud or sand. 

 The prostomium carries a pair of 

 linear groups of " eye-spots " ; the first 

 chaetigerous segment carries a trans- 

 verse row of tentacular filaments, and 

 the red gill -filaments commence on 

 the same segment. Common. C. ten- 

 taculatus Mont, is a larger worm, dark 

 red in colour, and is distinguished from 

 the preceding by the absence of eyes 



FIG. 174. Cirratulus tentacu- and by the fact that the tentacular 



filaments are on the seventh chaeti - 



gerous segment, while the gills com- 

 mence more anteriorly. Atlantic and the Mediterranean... 



Chaetozone setosa Mgrn. occurs in the North Atlantic. 

 Dodecaceria concharum Oerst. is about an inch in length, olive- 

 green or brownish in colour, and is not uncommon amongst 

 roots of Laminaria. It is stated to live also in tortuous tubes 

 bored in shells and stones, but whether it makes these tubes is 

 uncertain. The worm has two thick tentacular filaments, and 

 the thinner gills are only on four segments. Jfekaterobranchus 

 shrubsolii Buch. 1 is a small worm some ^ inch long, found at 

 Sheerness, where it occurs at low tide in soft mud ; here it 

 forms a loosely coherent tube, though it also moves freely in 

 the mud. Its chief features are (1) a pair of long, ciliated 



1 F. Buchanan, Quart. J. Micr. Sci. xxxi. 1890, p. 175. 



