ANNULOSA: GEPHYREA. 255 



the gullet, and all being united by longitudinal commissures. 

 Lateral locomotive appendages are usually present, but are not 

 composed of successive joints, nor are articulated to the body. 

 A true blood-vascular system is not developed ; but there is 

 usually a closed system of " pseudohaemal vessels." 



GEPHYREA. 



CLASS I. GEPHYREA ( = Sipunculoidea). Vermiform marine 

 animals, with usually elongated bodies which may be indistinctly 

 annulated, but are not segmented, and carry no locomotive append- 

 ages (beyond, occasionally, bristles]. Ventral nerve-cords not gang- 

 lionated ; sexes generally distinct ; a distinct metamorphosis in 

 development. 



The members of this class are generally known as " Spoon- 

 worms," and they form a connecting link between the Echino- 

 dermata and the Annelides. The body is worm-like, the in- 

 tegument sometimes ringed (fig. 124), but never divided into 



Fig. 124. Gephyrea. Syrinx nudus. (After Forbes.) 



distinct segments. There are no ambulacral tube-feet, nor 

 foot-tubercles ; but there may be bristles which act as locomo- 

 tive organs (as in Echiurus], while in Chcetoderma calcareous 

 spines occur in the integument. The outer layer of the in- 

 tegument is chitinous, and beneath the skin is a strong mus- 

 cular coat of longitudinal and circular fibres. The mouth is 

 placed at the front end of the body, and the ciliated alimentary 

 canal terminates in an anal aperture which may occupy the 

 hinder end of the body, or may be placed far forward on the 

 dorsal surface. A retractile or contractile proboscis is present, 

 and may be provided with bristles or tentacles. The intestine 

 is convoluted, and is suspended freely in a body-cavity, which 

 is filled with a corpusculated fluid, kept in circulation by 

 ciliary action. -A vascular (" pseudohaemal ") system may be 

 present, or in other cases is not developed. Respiration is 

 carried on by the general surface of the body, by hollow ten- 

 tacles placed round the mouth (Sipunculus), or by abdominal 



