POLYCLAD FLATWORMS — HYMAN 649 



Section Schematommata 

 Family Leptoplanidae Stimpson, 1857 



Stylochoplana minuta, new species 



Figure 2o-c 



Material: One specimen collected from algal washings in the in- 

 tertidal zone, Sept. 22, 1953, on Ifaluk Atoll between Elangalap 

 and Falarik Islets, Sta. 65-D-3. Another specimen, collected by D. 

 Reish, Sept. 4, 1956, on fronds of algae on the reef flat on Eniwetok 

 Atoll, Sta. E-79, was doubtfully assigned to this species. 



General features: This is a very small species; the Ifaluk 

 specimen was 5 mm. long, the Eniwetok specimen 4 mm. long. But 

 both specimens were seen to be sexually mature by the presence of 

 relatively large eggs in a lateral strand on each side (fig. 2a). The 

 form is typically leptoplanid, slender, elongated, rounded anteriorly, 

 tapering to a pointed posterior end. Tentacles are wanting. Both 

 specimens appeared colorless or white. The eyes of both specimens 

 are not arranged in tentacular and cerebral clusters, as common in 

 the Leptoplanidae, but form a single irregular row, of 15 eyes on one 

 side, 12 on the other, in the Ifaluk specimen (fig. 26). They were 

 not counted in the other specimen. Even in the cleared specimens 

 little could be seen of the interior structure except the presence of 

 eggs. 



CoPULATORY apparatus: The posterior end of the Ifaluk specimen 

 was removed and sectioned sagittally. The copulatory apparatuses 

 found therein are depicted in figure 2c. The gonopores are somewhat 

 distant from each other (about 0.5 mm.). The male gonopore leads 

 into a tubular, slanting male antrum that appeared to widen internally 

 around a probable penis papilla but these parts were imperfectly 

 present in the sections, hence their representation in figure 2c is 

 somewhat conjectural. The lining epithelium of the male antrum 

 is highly glandular, filled with coarse eosinophilous granules. The 

 presence of a penis papilla could not be definitely ascertained. There 

 is present an elongated oval prostatic vesicle with muscular wall 

 and glandular interior. Beneath its proximal end occurs an oval 

 muscular seminal vesicle; the connection of this with the prostatic 

 vesicle was vague in the sections but probably occurs as indicated 

 by the dotted lines in figure 2c. The expanded spermiducal vesicle 

 filled with sperm was seen entering the seminal vesicle. 



The female apparatus was in a better state of preservation than 

 the male apparatus and its details could be ascertained. The female 

 antrum ascending in a curve from the gonopore is continuous with 

 the vagina of which the distal part is remarkable for its thick mus- 



