424 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 2 



Mecoderus oligoplitis, new genus, new species 

 (Plates 46 and 47, figs. 108-110) 



Host: Oligoplites saurus (Bloch and Schneider) 



Location: Stomach and gills 



Locality: San Francisco, Ecuador 



Number: 10 specimens were collected, 8 from the stomach of 

 one fish, 2 from the gills of another 



SPECIFIC DIAGNOSIS OF MECODERUS OLIGOPLITIS 



Smooth-skinned, tailed hemiurids with much narrowed, elongated 

 anterior region and short, wide, plump posterior region containing most 

 of reproductive organs. Total length of body including extended portion 

 of ecsoma 5.872 to 7.425; greatest width 0.600 to 1.309. Forebody veiy 

 short; equally wide, 0.622 to 0.877 in length or somewhat less than %o 

 total body length. Anterior portion of body slender, flexible, very long, 

 3.105 to 4.455 in length, always more than half total body length, about 

 equally wide, widening abruptly to form body proper; distance from 

 acetabulum to wide portion of body 2.025 to 3.240. Wide portion of 

 body 1.087 to 2.025. Ecsoma partially extended in most specimens (from 

 0.810 to 1.433) but always at least partially retracted (wholly so in one 

 specimen). Oral sucker subterminal, large, somewhat longer than wide; 

 0.277 to 0.420 in transverse diameter. Several pairs of papillae around 

 oral aperture. Posterior edge of mouth with conspicuous lobes, 3 median 

 lobes evident, a smaller lobe on each side sometimes evident; total: 5 

 lobes. Acetabulum 0.337 to 0.450 in diameter; at least slightly larger 

 than oral sucker ; ratio may be up to 3 :4. 



Pharynx 0.202 to 0.225 in length by 0.165 to 0.195 in width; lateral 

 thickenings of phaiynx wall at anterior edge; esophagus subcircular, 

 capable of inflation into a saclike outpocketing or esophageal diverticulum 

 so vaiying in appearance as to suggest it is an inconstant structure (it is 

 probably an elastic bulb capable of expansion) ; ceca bow forward slight- 

 ly, then extend, rather close together, to extreme posterior end of ecsoma, 

 considerably wrinkled and folded in the partially extended ecsoma. 



Genital pore an inconspicuous transverse slit opposite middle of phar- 

 ynx. Testes smooth, subtriangular to ellipsoidal, close together, oblique, 

 at anterior end of widened portion of body. Seminal vesicle a thin-walled 

 sac, immediately anterior to and overlapping anterior testis, at anterior 

 border of widened portion of body. Pars prostatica, surrounded by pro- 

 static cells, coiled or sinuous, rather short, extending only a short distance 



