Introduction to Animal Morphology. 193 



hooks ; intestine usually spiral ; anus dorsal ; teeth none ; 

 skin netted with anastomosing muscle fibres (Sipunculus), or 

 papillose, with cylindrical (Phascolosoma), or clustered (Den- 

 drostomum) tentacles. Family 2. Aspidosiphonidae with 

 two dermal shields beside the proboscis, and a posterior 

 anus, ex. Aspidosiphon, Diesingia. Family 3. Priapulidae 

 proboscis retractile, ribbed ; tentacles none ; anus posterior; 

 tail bearing a tuft of hollow, pouch-like processes, and with 

 a pore into the body cavity (absent in Halicryptus) ; the pro- 

 cesses are thread-like in ten long rows in Lacazia. Anoplo- 

 somatum has cnidae. 



Order 2. Armata bristled, with a developed vascular 

 system. Family 4. Thalassemidae cylindrical or fusiform, 

 with a non-retractile proboscis above the mouth ; anus pos- 

 terior ; excretory organs opening into the intestine ; proboscis 

 short, undivided (Echiurus), or long, single (Thalassema), or 

 forked (Bonellia), or absent, but a tubularly protrusible mouth 

 instead (Ancistropus). Family 5. Sternaspideae ringed ; 

 abdomen flat, with a posterior horny shield, bristled round its 

 edge ; several girdles of bristles anteriorly ; anus dorsal, sub- 

 terminal, ending in a retractile papilla, with simple tubular 

 threads beside it, ex. Sternaspis. Family 6. Chaetodermidae 

 surface beset with spines ; gills 2, branched ; proboscis 

 retractile. 



CHAPTER XXVIII. 

 CLASS 6. ROTATORIA (Ehrcnberg}. 



MICROSCOPIC,* dioecious, aquatic, smooth, or slightly 



annulated animals. Tim rinifs arc most distinct when 



not fully chiti nixed, and arc often six, 



equal or unequal ; but tin r is no trace of visceral re- 



'..,-,',." long. 



