304 POLYCHAETA 



special cirri ; the parapodia are well-marked locomotor organs, 

 supported by acicula, and carry dorsal and ventral cirri. The 

 chaetae are usually jointed, though unjointed ones may coexist 

 with these ; uncini are never present. An eversible buccal region 

 leads into a muscular pharynx, which in the majority is armed 

 with chitinous jaws ; the septa and nephridia are regularly 

 repeated throughout the body. The worms lead a predaceous life, 

 and are mostly carnivorous ; a few form tubes. 



SUB-ORDER 2. The Spioniformia possess neither tentacles 

 nor palps ; the peristomium usually carries a pair of long 

 tentacular cirri, and extends forwards at the sides of the pro- 

 stomium. The parapodia project only to a slight degree ; the 

 dorsal cirri may attain a considerable size, and act as gills 

 throughout the greater part of the body. The chaetae are 

 unjointed ; uncini are only present in the aberrant Chaetoptervs.^ 

 The body may present two regions more or less distinctly marked 

 externally, but without corresponding internal differences. The 

 buccal region may be eversible, but there are no jaws. Septa 

 and nephridia are regularly developed. The worms are burrowers, 

 or tubicolous. 



SUB-ORDER 3. Terebelliformia. The prostomium is a more or 

 less prominent lobe (upper lip) with or without tentacles but 

 without palps. The peristomium may carry cirri or " tentacular 

 filaments." 2 The parapodia are feebly developed ; there are no 

 ventral cirri ; the dorsal cirri may exist and function as gills 

 on more or fewer of the anterior segments. The chaetae are 

 unjointed, and uncini are usually present. The buccal region 

 is not eversible; there are no jaws. The septa are usually 

 incomplete, with the exception of one strongly-developed " dia- 

 phragm " anteriorly ; the nephridia are dimorphic, those of the 

 anterior (prediaphragmatic) segments are of large size and are 

 excretory ; the posterior series are mere funnels, and act as 

 genital ducts. These worms are burrowers or tube-formers, and in 

 the majority the tube-forming glands are grouped on the ventral 

 surface of the anterior segments to form " gland-shields." 



1 The Chaetopteridae may have to be placed elsewhere in the system, as they are 

 peculiarly modified, and present features recalling the Cryptocephala, from which 

 it is possible they have descended. 



2 Meyer (Aft. Zool. Stat. Neapcl, vii. 1887, p. 669, note) suggests that the 

 tentacular filaments of Cirratulids are really prostomial, but have shifted back on 

 to the peristomium, or even farther. 



