322 



POLYCHAETA 



CHAP. 



of the prostomium, bears a pair of very long cirri (usually 

 termed " tentacles ") normally directed backwards, very mobile, 

 and more or less coiled. They are readily thrown off by the 

 animal. The notopodial cirri are long, finger-shaped, and curved 

 over the back ; they are vascular and ciliated, and function as 

 "gills.". The neuropodia project laterally. Both are usually 

 provided with a " podal membrane " along their outer margin. 

 There are no ventral cirri ; the dorsal chaetae are fringe 

 capillaries ; the ventral are " crotchets." The buccal region 

 eversible. The worms burrow in mud and sand. 



Spio seticornis Fabr. is a small worm less than an inch u 

 length, colourless except for the red blood in its vessels. It buik 

 long and flexible tubes of sand in the clefts of rocks and imdei 

 stones in the upper part of the littoral zone. The prostomium is 

 notched at the anterior margin. The gills commence on the 

 twelfth segment, and do not extend to the end of the body, 

 membrane-like cirrus exists also on the second chaetigerous seg- 

 ment. The podal membrane is adnate to the gill throughout its 

 extent. Four short anal cirri occur. Greenland and Scandinavia 

 Nerine is represented by two species, sometimes called " Kag- 

 worms." The genus is very similar to Spio, but the worms art 

 of larger size. The prostomium is compressed by the forwarc 

 growth of the peristomium, and appears as a ridge on the lattei 

 segment, extending downwards in front towards the mouth. The 

 " gills " commence on the second segment, and are continued u 



every segment except the hind- 

 most. Nerine (Scolecolepis] 

 vulgaris Jnstn. is readily distin- 

 guished from other species by 

 its somewhat T - shaped pro- 

 stomium. It is an extremely 

 common worm under stones and 

 amongst seaweed at low water. 

 It is some 3 or 4 inches in 

 length and more slender than 

 the following species. Its colour 

 stomium;] :, iv, following segments! is yellowish-brown, and the red 



gills directed upwards and back- 

 wards give the appearance of oblique red lines. The podal mem- 

 brane does not reach the tip of the gill. North Atlantic. It is 



Fig. 172. Nerine vulgaris Jnstn., enlarged. 

 (From Cunningham.) a, Prostomium ; 



e\ cirrus of peristomium 



"gill 1 



