xii SPIONIFORMIA TEREBELLIFORMIA 325 



Chaetopterus is highly phosphorescent (see p. 295). It 

 is further interesting on account of the green colouring-matter, 

 which is extracted by alcohol. Two commensal Polynoids occur 

 in the tube, viz. Polynoe glabra and P. cirrosa. The larva is 

 " mesotrochal " (with a ciliated ring round its middle), that region 

 of the body lying in front of the cilia giving rise to the region 

 A, whilst the rest of the body gives rise to regions B and C. 



FAM. 4. Magelonidae. This family includes only the very 

 peculiar worm, Magelona papillicornis Fr. MiilL, which lives 

 buried in sand, between tide-marks, in various parts of our coast 

 and that of the United States. Its chief features are the large, 

 flat, spoon-shaped prostomium ; the long peristomial cirri, slightly 

 expanded terminally, carrying papillae along one side; the 

 enormous, eversible buccal region, which is an important 

 respiratory organ. The blood is of a madder-pink colour, and 

 the blood-vessels in the thorax are greatly dilated. The body 

 of the worm is divisible into two well-marked regions, owing to 

 differences in the chaetae. 1 



FAM. 5. Ammocharidae. This family contains only one 

 species, Owenia filiformis D. Ch. Some of the anterior segments 

 are longer than the hinder ones, though the arrangement of 

 chaetae is alike throughout. The mouth is wide, like that of 

 Chaetopterus, and is surrounded, except ventrally, by a membrane, 

 so deeply notched as to give rise to flattened filaments containing 

 blood-vessels. These " gills " appear to belong to the peristo- 

 mium. The small worm in its sandy tube is plentiful on our 

 coasts in about 20 fathoms. Off Greenland and the Mediter- 

 ranean. 



Sub-Order 3. Terebelliformia. 



FAM. 1. Cirratulidae. These worms have a cylindrical body, 

 more or less attenuated at each end ; the segments are distinct, 

 and similar throughout, with capillary chaetae on each side in 

 two bundles, carried by small papillae. The prostomium is 

 conical, the peristomium usually without cirri. On more or 

 fewer segments the dorsal cirri are long and filamentous, and 

 function as gills. There is a single pair of anterior nephridia : 

 the septa and genital ducts are repeated throughout the hinder 

 part of the body. The worms usually live in burrows. 



1 For literature, see Benham, Quart. J. Micr. Sd. xxxix. part 1, 1896, p. 1. 



