AMPHINEURA 483 



Order 1. APLACOPHORA.* (Solenogastres.) 



Body worm-like, being more or less cylindrical and usually elongate, 

 and without a shell. The exceptionally thick cuticula contains calcareous 

 spicules which sometimes project above the surface and represent the shell 

 of the higher mollusks. On the ventral surface, except in Chcetoderma, is 

 a median longitudinal groove representing a rudimentaiy mantle cavity, 

 the two sides of which are formed by the mantle-folds. Within this groove 

 lies a ciliated ridge which represents the rudimentary foot. At the hinder 

 end of the body this groove widens to form the cloacal cavity, in which are 

 the anus, the two kidney pores, and the two gills. 



The mouth opens into a pharynx in which a radula and salivary glands 

 are usually present. The alimentary tract is straight. The nervous system 

 is more highly developed than in Chiton, and has a distinct brain and 

 numerous ganglia. The heart lies in a large pericardium at the hinder end 

 of the body; this cavity represents the coelom and communicates with the 

 cloacal cavity by means of a pair of nephridial tubes. The gonads are 

 paired and, except in Cli(Eto derma, hermaphroditic. They are sac-like in 

 structure and lie in front of the pericardium, into which they open. Their 

 products pass into the pericardium and through the nephridia to the outside. 



The Solenogastres are marine animals which live on or near the bottom 

 in from 20 to 1,000 fathoms, in various parts of the world. Many species 

 live on and among hydroids; others feed on crustaceans and many on 

 plants. 



The order contains 2 suborders, 13 genera, and about 30 species. 



Key to the suborders of Aplacopliora : 



fli Mid-ventral groove present 1. Neomeniina 



Oa No mid-ventral groove 2. Ch^todermatina 



Suborder 1. NEOMENIINA. 



Head and cloaca but little or not at all developed; mid- ventral 

 groove present, at the f orw^ard end of which is a large gland ; gills simple, 

 sac-like evaginations of the cloaca and not feathered; animals hermaph- 

 roditic ; nephridia unite and open to the outside through a single median 

 pore beneath the anus; radula sometimes wanting; intestine with lateral 

 pockets : 4 families and about 27 species. 



Family 1. NEOMENIIDAE. 



Body short and thick, with both ends alike; cloaca and mouth ven- 

 tral, the former with a row of short respiratory papillae around its edge; 



* See "Aplacophora," by H. A. Pilsbry, Man. of Conch., Vol. 17, 1892. 



