POLYCLAD FLATWORMS — ^HYMAN 583 



(Hyman, 1953a), Acanthozoon cannot become a subgenus of Pseudo- 

 ceros but would more logically be made a subgenus of Thysanozoon, 

 which would then include all pseudocerids witli dorsal elevations. 

 In fact, one may anticipate that difficulty must eventually arise in 

 determining when the elevations are low enough to fit into Acantho- 

 zoon and when tall enough to fit into Thysanozoon. This dilemma has 

 not yet arisen. Eveline Marcus (1955) has listed the species to be 

 transferred to Acanthozoon and this information therefore need not be 

 given here. I favor retaining the genus Acanthozoon for the species 

 listed by Marcus. 



Acanthozoon albopapillosus, new species 



Figure 14a,6 



Material: One damaged specimen collected July 22, 1954, in the 

 Palau Islands. No other data available. 



General characters: The specimen is nearly circular but the 

 posterior part is missing, hence the shape of the intact worm was 

 probably oval. The sides are also damaged. The tentacular folds 

 ai"e poorly preserved. A pair of eye clusters can be seen in the tentac- 

 ular region and behind them is a single oval cluster of cerebral eyes. 

 The ruffled pharynx is large and voluminous, so much so that damage 

 and rupture are suggested. Behind the pharynx is seen the sucker 

 whose pointed shape is probably unnatm'al. There are no indications 

 of any part of the reproductive system, hence this must be a large 

 worm when intact and mature. Because of extensive damage the 

 dimensions of the specimen are of little value. In the longitudinal 

 axis it measures 26 mm., in width 25 mm. anteriorly, 35 mm. poste- 

 riorly. Despite damage the specimen is worth naming because of the 

 distinctive color pattern. It is black with flesh-colored marginal 

 band and rounded pinkish buff areas all over the dorsal surface. These 

 areas are in general smaller towards the periphery. The pattern is 

 indicated on the right side of figure 14a. The entu'e dorsal surface is 

 thickly strewn with small rounded white papillae, hence this surface 

 appears dotted with white to the naked eye. These papillae are 

 indicated in the upper left of figure 14a. The ventral surface is pale 

 except for a wide black band subtending the paJe margin. This 

 black band is shown on an upturned fold in the lower left of figure 

 14a. It is quite conspicuous when the worm is viewed from the 

 ventral side. 



Papillae: A small bit of the worm was removed and sectioned 

 to see the structure of the papillae. The histology of the papillae of 

 Acanthozoon was given by Kato (1934) for A. micropapUlosus and by 

 Eveline Marcus (1955) for A. hispidus. Both find that the papillae 

 are elevations of the mesenchyme covered with a cuboidal epithelium 



472590—59 4 



