CHAPTER XI 



PHYLUM GEPHYREA 



IN the older books of zoology under the head of Annelida a 

 subdivision is included which is termed Gephyrea. The Gephyrea 

 were defined as Annelida which had lost all signs of the metameric 

 segmentation of the body and in which moreover the ventral nerve- 

 cord is uniform in diameter throughout and in which there are no 

 septa dividing successive coelomic cavities from one another. What 

 remains of Annelid character is as follows: (1) The possession of 

 a dorsal brain, nerve-collar and ventral nerve -cord. (2) The pos- 

 session of a spacious body-cavity or coelom from whose walls, in the 

 majority of cases, the genital cells are produced. (3) The possession 

 of tubes opening to the exterior which in most cases combine the 

 functions of excretory organs and genital ducts. The group used 

 to be divided into Gephyrea nu da which burrowed in sand and 

 mud, and Gephyrea tubicola which lived in clear water sheltered 

 in leathery tubes secreted by the ectoderm. The Gephyrea nuda were 

 further divided into (a) Armata, which possessed a smaller or larger 

 number of chaetae embedded in the skin and which had an elongated 

 praeoral lobe or prostomium, and into (6) Inermia which were 

 devoid of chaetae and of prostomium, but in which the anterior part 

 of the body could be turned outside in or introverted like the finger 

 of a glove. 



Modern research seems to indicate that in the Gephyrea nuda 

 we have confounded together three quite distinct groups whose 

 connection with one another is more than doubtful. These are 

 as follows : (1) The Echiuroidea which possess chaetae embedded 

 in the skin, a much elongated, grooved and ciliated prostomium, 

 and in which the anus is at the posterior end of the body. (2) The 

 Sipunculoidea in which there is no prostomium, but in which the 

 front part of the body can be introverted into the hinder part, and 

 in which the anus is situated far forward on the dorsal surface of 



