THE BURROWING BARNACLES (CIRRIPEDIA: ACROTHORACICA) 151 



Phylogeny 



The multiplicity of families in the order Acrothoracica appears to 

 be a result of emphasis on different features which appeared at the 

 time to be of major importance. I have retained these families up to 

 the present writing for two reasons: they could be very nicely dif- 

 ferentiated by the number of terminal cirri and caudal appendages, 

 and I was optimistic that many new species of acrothoracicans would 

 be found and new genera would be erected. For this reason, I erected 

 the new family Utinomiidae. My hopes regarding the many new species 

 seems to have been well founded, but these species have fit nicely into 

 existing genera, and it now appears that the order is "top heavy" with 

 families, most of which are monotypic. 



I believe that we would be putting the systematics of the order in 

 more realistic terms if we rejected most of these families, and retained 

 only the three major extant groups represented by the Cryptophialidae, 

 the Trypetesidae, and the Lithoglyptidae, the latter incorporating the 

 old families Berndtiidae, Balanodytidae, Kochlorinidae, Utinomiidae, 

 and Chytraeidae. 



It is likely that the members of the fossil form-families Zapfellidae 

 and Rogerellidae also would fit into the family Lithoglyptidae if the 

 animals themselves were known. 



Although there remains little need for the suborders Pygophora and 

 Apygophora, when there are only three extant families to incorporate 

 within them, they can be retained without problems. It seems obvious 

 that the Trypetesidae, the sole family of the Apygophora, is more 

 specialized and divergent than the two families in the Pygophora. 



There are several clear trends in the order Acrothoracica, primarily 

 in the direction of reduction of appendages and a simplification of 

 organ systems. One specialization is in the loss of thoracic and caudal 

 appendages, with a change from biramous to uniramous condition m 

 the suborder Apygophora. The grouping of the thoracic cirri onto the 

 end of the thorax seems to necessitate the adaptation of the first pair 

 of cirri toward removal of food from these closely associated thoracic 

 appendages. The members of this pair are called the "mouth cirri." 



In thoracican barnacles the cirri are spaced far enough apart so that 

 they move in relation to each other as the thorax is flexed and extended 

 in a feeding motion. Thus food is passed along to the progressively 

 smaller cirri near the mouth, to be seized by the mouthparts and 

 ingested. The acrothoracicans, on the other hand, have most of their 

 cirri bunched at the terminal end of the thorax, and hence movement 

 in relation to one another is impossible, and food material cannot be 

 transferred from one pair of cirri to another. They would, therefore, 



