264 
PACIFIC SCIENCE, Vol. XVII, July 1963 
Fig. 3- Plathymenia branchiosa. Sta. 2324. 
without a radula but has unicellular subepithe- 
lial dorsal diffuse) and very small ventral 
salivary glands; a well-developed oesophagus 
with villi is surrounded by numerous gland- 
follicles. The mid-gut is largely divided into 
diverticles, and the gonads also have large 
lateral diverticles. The brain is bilobed, has a 
dorsoterminal organ of the Entonomenia type. 
The shell-gland has subepithelial glands; there 
are no copulatory organs. 
The genus is known for a single species, 
P. branchiosa Schwabl. 
Plathymenia branchiosa Schwabl, 1961 
Fig. 3 
Schwabl, 1961 b, p. 100, figs. 1-5. 
COLLECTION: 2324 (1) in 400 fm, with 
Crystallophrisson riedli n. sp. 
DIAGNOSIS (translated from the German): 
The species has the characteristics of the genus. 
The body is flattened ventrally; length of the 
body is 10 mm, width 2.5 mm. There is no 
dorsal keel but a tapering front end and a 
broadened or rounded hind end. Color in alco- 
hol is muddy gray. The cuticle is heavy and 
there are no epidermal papillae. The spicules 
are hollow, straight or slightly curved needles, 
the radial ones up to 700 /x long, the tangential 
ones up to 100 /x. The ventral furrow is dis- 
tinctly separated from the cloacal opening, one 
single ventral fold. About 30 sensory setae in 
epidermal pockets surround the atrial opening. 
The muscles are very weak. The parenchyma 
of the hind end has a gelatinous basic sub- 
stance. The pericardium is very large and has 
short distal appendages. The ventricle for half 
its length is dorsally connected with the peri- 
cardium, the auricle is free, and has two atrio- 
ventricular openings. A large cloacal chamber 
has about 110 simple radial gill-folds. There 
are no abdominal spicules. 
DISTRIBUTION: This species is known 
through a single specimen from the San Pedro 
area, in 400 fm, in mud with glass sponge. 
FIG. 4. Prochaetoderma californicum n. sp. Sta. 
2802-54. 
