757 



ON THE CILETOSOMATID.E, WITH DESCRIPTIONS 

 OF NEW 8PECIE8, AND A NEW GENU8 FROM 

 THE COAST OF NEW SOUTH WALES. 



By Vera A. Irwin-Smith, B.Sc, Science Research Scholar 

 IN THE University of Sydney. 



(Plates xliv.-L, and 59 Text-figures.) 



Introduction. 



The C hfHtosoviatidcE are a group of curious, little, free-living, 

 marine worms, which appear to be related to the Nemathel- 

 minthes, more especially to the Nematoda, though they cannot 

 at present be directly included in any recognised class. They 

 have been found only along the shore line, and at shallow depths 

 off the coast, where they live on the rocky or stony sea-floor, 

 among clumps of seaweed and shell-tish; and creep along by 

 curious, looping movements like those of a leech. In this move- 

 ment, they are assisted by adhesive seise situated in rows on the 

 undersurface of the body towards the posterior end, and in a 

 fringe round the anterior margin of the "head-swelling." These 

 setye, and the enlargement of the anterior end of the body to 

 form a head-like swelling, constitute two of the most prominent 

 characteristics of the animal, by which it is distinguished from 

 any other known worm. All the ChcetosomatidcH are very small, 

 rarely exceeding 1 mm. in length, and cannot be detected by the 

 unaided eye. 



Historical. 



They escaped observation until 1863, when Claparede^l) dis- 

 covered a single female specimen on the coast of Normandy^ To 

 this, he gave the name Chcetosotua ophiocephalu7n. 



Three years later, Metschnikofi' found them in considerable 

 numbers in the Mediterranean Sea, near Salerno; and, in 1867, 

 published a brief description (2) of a species differing slightly from 

 that found In' Claparede. 



