Monogenetic Trematodes, I — YAMAGUTI 
Vitellaria co-extensive with intestinal limbs ex- 
cept for their posteriormost portion. Gill para- 
sites of marine teleosts. 
TYPE SPECIE S: P. sphyraenae n. sp., on Sphy- 
raena barracuda; Hawaii. 
17. Areotestis sibi n. g., n. sp. 
Fig. 13 
HABITAT: Gill of Parathunnus sibi (type host), 
Neothunnus macr op terns, and Phunnus alaionga; 
Hawaii. 
HOLOTYPE: U. S. Nat. Mus. Helm. Coll., S.Y. 
No. 17. 
DESCRIPTION (based on 16 whole mounts): 
Body proper widened from level of anterior end 
of ovary to cotylophore, 11-25X4.5-16 mm, 
abruptly narrowed anterior to ovary and grad- 
ually tapering toward head which is 0.11-0.21 
mm in diameter. There are 63-105 clamps ar- 
ranged in an oblique row along entire posterior 
margin of body proper, whose posterior ex- 
tremity is prolonged into a conical appendage 
bearing two pairs of hooks; clamp skeleton con- 
sisting of two pairs of arcuate lateral arms, a 
pair of short basal arms, a pair of accessory 
sclerites and a median spring; longer prong of 
median spring anchor-shaped, but shorter prong 
slightly truncate apically and bearing simple, 
paired, and a terminally bifid, unpaired, poorly 
sclerotized, apical pieces just beneath the simple 
accessory sclerites. Of the caudal hooks the outer 
pair is 40-54/a long and the inner pair 22-30/a 
long, both with a very prominent guard and 
a long, well-curved blade. Head end usually 
rounded, with wide mouth aperture ventrally; 
at the bottom of the buccal cavity is a pair of 
comparatively small, aseptate, muscular suckers 
20-33/a by 27-50/a; pharynx oval, 45-60 X 35- 
50/a. Esophagus simple, 0.6- 1.6 mm long, bifur- 
cating a little behind genital pore; intestinal 
limbs simple anteriorly, sooner or later giving 
diverticles which unite with one another and 
form network extending throughout enlarged 
portion of body proper, enclosing variable num- 
ber of testes in the meshes. 
Testes rounded, separated into 70-170 flat 
areolae, very irregular in size and outline, com- 
mencing at junction of anterior with middle 
third of body; each areola comprising 1 to 20 
testes. Vas deferens strongly twisted posteriorly 
89 
when distended with sperm, running in inter- 
intestinal field dorsal to uterus but more loosely 
winding anteriorly and differentiated into a 
sigmoid pars prostatica surrounded by prostate 
cells a short distance posterior to genital pore. 
Ejaculatory duct narrow, winding; cirrus pouch 
funnel-shaped, containing bulbus cirri at its 
widest anterior portion, continued into genital 
atrium; cirrus consisting of a basal bulb 45-50/a 
in diameter and an apical bundle of elongate 
cuticular shingles projecting into genital atrium. 
The structure and number of the shingles could 
not be made out, because they are massed tightly 
together. They appear to arise from the anterior 
border of the truncate conical, membranous ex- 
tension of the bulbus cirri. Genital atrium 65- 
93g in diameter, provided with thick wall of 
circular muscle fibers, provided inside with a 
crown of 13 to 18 hooks which measure 40-55/a 
in length including the cylindrical base l4-19g 
long, each being bifid at the incurved tip. Geni- 
tal pore ventral to esophagus, 0.36-0.75 mm 
from head end. 
Ovary tubular, arising from posterior end of 
interintestinal field at anterior end of posterior 
third of body in form of a compact V-shaped 
mass of very small primordial germ cells, ex- 
tending forward just medial to left intestinal 
limb, turning back on itself at about midbody 
and descending along medial side of ascending 
portion; as a whole the ovary measures 2. 6-6. 5 
mm in length and 0.12-0.6 mm in maximum 
width. The germiduct arising from the distal 
end of the ovary joins the genito-intestinal duct 
on the left and then the vitelline reservoir on 
the right at the posterior end of the middle 
third of the body. Genito-intestinal duct fre- 
quently forming a rounded or elliptical seminal 
receptacle 12-25/a in diameter near its origin 
from germiduct, opening into left intestinal 
limb, usually at a level a little anterior to its 
origin. Eggs fusiform, thick-shelled, 175-265 X 
70-120/a in mounted condition, produced at 
each end into rigid process which is 70-200/a 
long and may or may not terminate in a disc 
8-25/a in diameter. Vagina entirely lacking. Vi- 
tellaria completely co-extensive with intestine 
and its network; their rudimentary follicles com- 
mencing along esophagus at varying levels 
posterior to genital atrium; vitelline reservoir 
Y-shaped, its stem 0.45-1.3 mm long, imme- 
