THE BURROWING BARNACLES (CIRRIPEDIA: ACROTHORACICA ) 11 



The cirriped can, at most, be considered a modest shell-weakening 

 pest, and in general does little if any harm to the host. All species of 

 the order collect food without taking from or giving anything of 

 value to the host. 



The excavation of the burrow is allometric, with an initial elonga- 

 tion of the slit preceding a deepening and widening. This provides an 

 initial access to the outside with room to manipulate the cirri before 

 the extensive brood pouch and ovarian area are developed. The 

 growth rate is difficult to estimate, and is apparently typical of 

 invertebrates in being largely dependent on temperature and food 

 availability. I have kept Trypetesa lateralis alive in shallow dishes in 

 a cold box for over a year, with no perceptible increase in burrow 

 size. 



A major structural element within the burrow is the attachment 

 area, which provides the fulcrum for mantle movement already 

 mentioned. The cement affording the attachment apparently is 

 provided by glands on the dorsal mantle area (cf . Lithoglyptes spinatus 

 Tomlinson and Newman, 1961). The cemented area may be small if 

 the mantle has a conspicuous horny "knob," or large if a horny 

 "disk" is on the mantle. Acid will release the mantle at the point of 

 attachment, but it is not certain whether this involves releasing the 

 cement or destroying the shell surface to which the cement is applied. 



It is clear that all species examined are cemented into the burrow, 

 and no species hangs in the burrow by hooks or spines as suggested 

 by some early workers. 



The Mantle 



The conspicuous features of the exterior of the mantle include the 

 apertural armament, the teeth, the lateral bars if present, and the 

 cemented horny disk or knob. 



The cemented area was just discussed under the subject of the 

 burrow. The mantle, being cemented firmly to the burrow wall, 

 cannot molt in this area. As a consequence, many layers of exuviae 

 build up, becoming "horny" in appearance. Since this cemented area 

 often expands with the growth of the female, the consecutive layers 

 usually are not deposited directly on top of each other, but in eccentric 

 rings with the wider gaps between rings posteriorly. Males often are 

 attached to the margins of this homy disk. 



The flattening of this attachment area is, perhaps, a consequence 

 of the inability of the center of the area to continue to abrade the 

 shell, while the edges do continue to abrade. Hence, the otherwise 

 rounded mantle sack usually is flattened in the attachment area. 



327-241 O - 69 



