GASTROTRICHA 243 



instance, in roof gutters and amongst moss. The group to which these 

 forms belong is called the "bdelloid" or leech-like rotifers, because 

 they not only swim, but progress by a looping method like that of 

 Hydra or a leech. 



PHYLUM GASTROTRICHA 



Minute wormlike, unsegmented animals, with certain tracts of the 

 skin ciliated, the cuticle often forming bristles and scales; a non- 

 cellular hypodermis, forming adhesive papillae, longitudinal muscle 

 cells which do not form a continuous sheath; straight alimentary 

 canal consisting of a muscular pharynx like that of the nematodes 

 and a mid gut without diverticule ; a pair of nephridia in freshwater 

 representatives; a nervous system consisting of a cerebral ganglion 

 and two lateral cords ; hermaphrodite individuals in one division of 

 the phylum (Macrodasyoidea) and parthenogenetic females in the 

 other (Chaetonotoidea) ; the single female aperture opening near 

 the anus, and the male aperture when present variable in position. 

 Development direct and cleavage total. 



These small animals (Fig. 172) are usually elongated and creep 

 or swim by means of their cilia or move in a leech-like manner 

 using their musculature. They feed on minute animals and plants 

 which are sucked in by the pharynx. 



The Gastrotricha have features in common with the Rotifera, such 

 as the external ciliation, the bifid foot and the excretory system with 

 flame cells, but in the character of the gut they recall the Nematoda. 



