128 



THE CRUSTACEA 



MORPHOLOGY or APODA. 



This order was established by Darwin for the reception of a 

 single species, Proteolepas bivincta, of which he found a solitary 

 specimen parasitic within the mantle-cavity of a pedunculate 

 Cirripede, Alepas cornuta, from the West Indies. No further 

 specimens have been seen by later investigators. 



Proteolepas (Fig. 79) is referred to the Cirripedia mainly because 

 it possesses adhering antennules which agree minutely with those of 



A. 



FIG. 78. 



Dendrogaster astericola. A, young specimen ; B, older specimen ; C, Cypris larva. a' r 

 antennule ; ae, aesthetasc ; abd, abdomen ; br, supra-oesophageal ganglion ; /, caudal furca ; 

 m.c, mouth-cone ; p, rudiment of penis ; st, stomach, sending a diverticulum into the shell- 

 valve ; v.n, ventral nerve-mass. (After Knipowitsch.) 



normal Cirripedes. It differs most conspicuously in the absence of 

 any trace of a mantle and of thoracic limbs. 



The body is elongated and maggot-like. It is divided into 

 eleven segments, but as one of the segments is in front of that 

 bearing the antennules, it seems clear that this segmentation does- 

 not express the number of true somites present. The mouth-parts, 

 borne on the first " segment," seem to be adapted for piercing and 

 sucking. The labrum partly ensheathes the gnathites, of which 

 there appear to be two pairs, turned outwards, and serrated on the 

 outer margin. From the dorsal surface of the second segment 



