Solenogaster Mollusks— Schwabl 
275 
Fig. 20. Crystallopbrisson riedli. Sta. 2838. 
is frequently more contracted than the anterior 
half (Fig. 20). The dorsoterminal organ is 
very short but continuous with the opening 
of the cloacal chamber. The buccal plate is 
rounded and has a dorsal cleft containing the 
mouth opening. The abdominal gland zone is 
present. Spines (Fig. 19) are of medium size 
and have a marked keel. 
Dorsal, lateral, and ventral retractor muscles 
are present at the front end; the longitudinal 
muscle layer in the prothorax is gradually split 
up into numerous bundles. The gill retractors 
are short; the ventral anterior ones are very 
heavy; the second pair of dorsal posterior ones 
are lacking or, if present, attach to the cloacal 
wall between the gills. Lateral, ventral, and 
part of the dorsal anterior gill retractor unite 
before entering the gill, which gives the trans- 
verse section of the gill a very characteristic 
appearance. The gill axis consists of a bulbous 
ventral half, and a very slender dorsal half. 
The posterior vertical diaphragm is unusually 
strong. 
The nervous system is typical; the buccal 
nerve leaves the common root very soon. The 
fore-gut has a strong circular and longitudinal 
muscle layer, circular in outline. Numerous 
buccal glands occur behind the sphincter mus- 
cle. All three kinds of salivary glands are pres- 
ent but the ventral ones are very small. The 
radula is typical. Granular cells in the liver 
are not only concentrated on the dorsal wall 
but irregularly distributed. The circulatory or- 
gans are typical, with two atrioventricular open- 
ings. The gonopericardial duct is fairly long 
and curved; the ciliated part of the gonoducts 
is comparatively long. The openings of the 
gonoducts are mostly on flat papillae, and their 
epithelium is not continued on the wall of the 
cloacal chamber. 
FIG. 21. Crystallopbrisson inf latum. Characteristic 
spicules from body regions a, b, c, and d. 
