Life Cycle of Mesostephanus appendiculatus 
(Ciurea, 1916) Lutz, 1935 (Trematoda: Cyathocotylidae) 1 
W. E. Martin 2 
For a number of years, the author has been 
studying trematode larvae which develop in the 
California horn-shell snail, Cerithidea calif ornica 
Haldeman. One of these, a pharyngeate, fur- 
cocercous cercaria, proved to be the larva of 
Mesostephanus appendiculatus. The adults of 
this species were first described from the small 
intestines of Rumanian cats and dogs by Ciurea 
(1916). Ciurea, however, placed this species 
in the genus Prohemistomum. Price (1928) 
found this parasite in the small intestine of a 
dog that had lived in the vicinity of Washing- 
ton, D.C. Lutz (1935) transferred this and 
some other species to his new genus, Mesoste- 
phanus. , naming M. fajardensis (Price, 1934) as 
type species. Dubois (1953) includes the fol- 
lowing species in the genus Mesostephanus: 
M. fajardensis (Price, 1934); M. appendicula- 
tus (Ciurra, 1916); M. appendiculatoides 
(Price, 1934); M. cubdensis Allegret, 1941; M. 
haliasturis Tubangui and Masilungan, 1941; and 
M. longisaccus Chandler, 1950. Caballero, Gro- 
cott, and Zerecero (1954) added M. micro- 
bur sa from the intestine of Pelecanus occiden- 
talis calif ornicus. Dubois (1953) believes that 
the members of the genus are natural parasites 
of certain fish-eating birds and accidental par- 
asites of dogs. 
MATERIAL AND METHODS 
Infected Cerithidea californica were isolated 
in finger bowls. Emerged cercariae were studied 
1 These studies were aided by a contract between 
the Office of Naval Research, Department of the 
Navy, and the University of Southern California, NR 
165-252. Manuscript received June 9, 1959. 
The opinions and assertions contained herein are 
the private ones of the author and are not to be con- 
strued as official or reflecting the views of the Navy 
Department or the naval service at large. 
2 Biology Department and Hancock Foundation, 
University of Southern California, Los Angeles. 
alive and as fixed and stained whole mounts. 
Cercariae were fixed without pressure by forci- 
bly ejecting them into cold Bouin’s solution. 
Earlier larval stages and percentages of infec- 
tion were obtained by crushing snails. Unin- 
fected Fundulus parvipinnis parvipinnis (Gi- 
rard ) and Gillichthys mirabilis Cooper were col- 
lected in an isolated pool where there were no 
snails. These fish were exposed to cercariae and, 
following a lapse of 2-3 weeks, were fed to 
hatchery-raised chicks. The chicks were exam- 
ined 9 days after the experimental feeding. The 
adult worms obtained were fixed in Bouin’s 
solution under slight cover-glass pressure. Lar- 
val and adult stages were stained with para- 
carmine and mounted in Permount. 
All measurements are in millimeters. 
OBSERVATIONS 
The sporocysts and cercariae of Mesostepha- 
nus appendiculatus develop in the digestive 
gland of the brackish- water snail, Cerithidea 
californica. During a 12 -month survey (Mar- 
tin, 1955), in which at least 1,000 snails were 
examined each month, only 7 infections of this 
parasite were found in 12,995 snails. 
sporocyst ( Fig. 2 ) : Mother sporocysts were 
not observed. Daughter sporocysts are saccular 
and elongate. Measurements of 20 stained and 
mounted specimens are: length 1.368-3.355, av. 
2.38; maximum width 0.173-302, av. 0.236. 
The wall of the sporocyst has transverse con- 
tractile bands. At intervals there are thicker 
bands which give a false appearance of seg- 
mentation. One end of the sporocyst has a thick 
wall which is traversed by a birth canal. 
CERCARIA (Figs. 3, 4): The cercariae are 
nonoculate and furcocercous. Though they lack 
eyespots, they show positive phototropism. The 
body surface is covered with minute, quincun- 
cially arranged spines and scattered papillae 
278 
