18 UNITED STATES NATIONAL MUSEUM BULLETIN 296 



to each other to any appreciable degree, and hence cannot move the 

 food progressively toward the mouth as is done in the thoracicans. 

 Probably for this reason one pair of cirri is isolated near the mouth 

 (hence the name "mouth cirri") and almost certainly serves to remove 

 the food from the terminal cirri by wiping action. Perhaps the comb 

 collar also serves as cirral combs or wipers when it is pressed 

 against the cirri by the mantle operculum. This latter action would 

 not seem to aid in feeding other than to keep the cirri clean. The excep- 

 tion to the function of the mouth cirri described is to be found in the 

 members of the family CryptophiaUdae, where those mouth cirri 

 present are reduced to mere stumps with a few hairs. They have 

 instead a well-developed labrum, which extends in a long tongue up 

 to and even beyond the mantle aperture. The labrum is hairy on the 

 ventral surface and lateral margins, and could serve to direct food 

 material to the mouth, once it has been brushed from the terminal cirri. 



The mouthparts consist of a pair each of mandibles and first and 

 second maxillae. The former are strongest, with heavy teeth along the 

 cutting edge, and they usually possess fine hairs along the ventral 

 and posterior surfaces and angles. The first maxillae typically have 

 two (or three) strong spines at the anterolateral angle, a pronounced 

 gap or diastema, and an array of finer spines and hairs on the pos- 

 teromedial angle. A long apodeme connects the first maxilla to a 

 more medial fulcrum. 



The second maxillae, placed close together at the posterior end of 

 the mouth field, are soft and rounded with a dense coat of hairs. 

 Haired "keels" often extend from the medial edge of the second 

 maxillae dorsally between the bases of the first maxillae. 



The mouth itself is immediately below the chitinized posterior 

 curvature of the labrum, and leads to a dorsally directed muscular 

 esophagus. 



The esophagus makes a dorsal bend around a heavy transverse 

 adductor muscle, and then it leads directly into the stomach of all 

 aero thoracicans except the cryptophialids. In the latter a heavy 

 triturating mill, called a "gizzard," directly precedes the stomach. 



The stomach is large, glandular, and relatively nonmuscular. It 

 may have one or more digestive glands extending from it. 



In the suborder Pygophora a simple tube-hke intestine leads to an 

 anus between the terminal cirri on the dorsal side. The suborder 

 Apygophora, represented by the unique family Trypetesidae, does not 

 possess an intestine or anus. 



In those acrothoracicans having a pair of caudal appendages, they 

 are uniramous, short, and flank the anus. They were once called anal 

 appendages, and perhaps serve the function of clearing the anal area 

 of debris. Many species are without them, however. 



