THE BURROWING BARNACLES (CIRRIPEDIA: ACROTHORACICA ) 23 



A heavy set of muscle bands typically extends from the body near 

 the upper attachment disk to the dorsal end of the orifice. This 

 retractor oriUcii would have the function of pulling the body down into 

 the mantle sac. 



The muscles of the body proper are numerous and complicated. 

 Utinomi (1960) separates them into three groups: the longitudinal or 

 extensors, the oblique or flexors, and the transverse set. The first two 

 groups are paired. The most obvious and typical sets of muscles include 

 the retractor corporis which originates in the dorsal opercular muscle 

 mass and inserts along the anterior dorsal thorax, more or less con- 

 tinuous with the longitudinal or longissimus corporis along the dorsal 

 thorax to terminal cirri. The adductor capitis and protractor corporis 

 arise in the muscle mass of the dorsal opercular area, the former in- 

 serting on the head and mouthparts and the latter on the sides of the 

 thorax. 



A variable number of transverse muscles connect the body walls of 

 both sides of the thorax, especially anteriorly. One lies just ventro- 

 posteriorly to the curvature of the esophagus. This transverse muscle 

 is of particular interest, in that a similar muscle is found in thoracicans 

 on the dorsoanterior side of the esophagus curve, except in the genus 

 Ihla. This is discussed in the genus Cryptophialus by Berndt (1907a) 

 and by Batham and Tomlinson (1965). 



The muscles of the mouthparts are complex, but in general are 

 similar to those of the thoracicans. 



The muscles of the cirri are not as well developed as in the thoraci- 

 cans, and Utinomi (1960) suggests that they therefore cannot flex 

 their cirri as far as can the thoracicans. This is substantiated by my 

 own field observations on several species of both orders. 



Before the muscles can become useful characteristics in under- 

 standing the systematics of the order Acrothoracica, they will have to 

 be thoroughly examined in many species, ideally by one worker. The 

 present study is not adequate for this comparison, inasmuch as most of 

 the material was recovered dried. The musculature cannot be carefully 

 considered in dried material. The designation of specific muscles is 

 extremely tenuous, inasmuch as small strands of muscle are scattered 

 about the body and mantle, and the designation of particular strands 

 as major muscles is often arbitrary. The presence of an orificial knob 

 in some species makes the designation of these muscle masses associated 

 with the orifice and attachment processes and disks quite diflScult. 



The muscles are in no way as definitive a characteristic as a cirral 

 count. Whether the muscles become useful in designating natural 

 groups remains to be seen, but at present 1 am doubtful. 



