THE BURROWING BARNACLES (CIRRIPEDIA: ACROTHORACICA ) 57 



This species is a typical lithoglyptid except for the mantle aperture 

 armature. The genus Lithoglyptes appears to be troublesome in the 

 variability of the mantle armament, but the existing species of the 

 genus are differentiated largely by this characteristic, which is of 

 sufficient complexity and stability to be useful if fully mature speci- 

 mens are found. 



This species was found in association with L. spinatus. The latter 

 had unmistakable characteristics precisely as described, and was 

 found in another Tridacna maxima from the same locality. Sufficient 

 variation exists between these two species to establish a new species. 

 The name is derived from the bent spines on the aperture. 



The aperture is long, measuring an average of 0.69 mm from ori- 

 ficial knob to comb collar. This is 63 percent of the greatest mantle 

 width, as compared to 33}^ percent for L. hicornis, 25 percent for 

 i. ampulla, and 50 percent for L. spinatus. Two prominent spines 

 arise in about the middle of the apertural lips and bend anteriorly 

 at their tips. These spines are equipped with bifid teeth and long 

 bristles. On the left lip a strong conical elevation, topped by several 

 strong teeth and many bristles, arises near the posterior end. The 

 remainder of the lips, analogous to the opercula of thoracican cirripeds, 

 are armed with numerous bifid teeth on simple small spines, with 

 scattered bristles at the posterior end and the typical comb collar at 

 the anteroventral end. The sides of the apertural area are scaly, 

 with the scales in places discernable as rows of extremely fine dots. 

 A weak pair of lateral bars arise from the base of the spines and 

 extend posteroventrally along the sides of the mantle. 



The rest of the mantle is equipped with small teeth, mostly 

 simple or bifid, but occasionally trifid. The anterior sides of the mantle 

 are almost devoid of these, but bear short bristles along the ventral 

 surface. 



The internal structures are typical of the genus. The mouth cirri 

 are faintly segmented into three and one segments for the anterior 

 and posterior rami, respectively. The mouthparts appear very similar 

 to those of L. spinatus. The caudal appendage is two-segmented. 

 Larvae are retained in the female mantle cavity until the cyprid stage. 



Segment counts are difficult, inasmuch as the distal ends are broken 

 off of some rami of every specimen dissected. A pooled count follows : 



