MALAYSIAN PARASITES XIII 
STUDIES OF LARVAL TREMATODES FROM SNAILS 
By 
A. A. SANDOSHAM 
First Batch of Live Snails 
In order to complete the morphological and life-history studies of the member of the 
“Elvae” group causing cercarial dermatitis in man in Malaya reported in the preceding paper 
(Sandosham 1953), a batch of fresh-water snails was flown to London. 
About 50 snails, kindly identified by Dr. W. J. Rees of the British Museum as Lymnaea 
crosseana Mabille, had been packed alive in moist charcoal at Singapore and the journey to 
London had taken five days. All but six were found dead. 
The five snails were transferred to some fresh water in separate 3" x 1" tubes and exposed 
to bright fight. Three of the snails discharged cercariae. Snails 1 and 2 discharged two 
different types of cercariae. One was an echinostome with 37 collar spines and the other a 
furcocercous variety. Snail 3 discharged two types of echinostome cercariae, one with 37 
collar spines and the other, which was slightly smaller, with 43 spines. 
Description of Cercariae 
Both types of Echinostome cercariae swim powerfully at random by the vigorous movements of the 
tail, the body being doubled up by bending ventrally while swimming. When not swimming actively, 
the body straightens out and the cercariae tend to gravitate to the bottom of the container. On a slide 
and in the bottom of the container, the cercariae creep about fairly rapidly by the alternate use of the two 
suckers. They remain active for 8 to 10 hours after which they tend to collect at the bottom and finally 
die at the end of about 24 hours. They exhibit no evidence of phototaxis. 
Echinostome Cercaria with 37 Collar Spines (Fig. 1 ) 
The body is elongate, pointed anteriorly and has its greatest width at about the level of the ventral 
sucker. The body and, to a lesser extent, the tail are capable of a considerable degree of extension and 
contraction. The measurements given below are of specimens fixed in formalin. The body measures 0.3 
to 0.43 mm in length and 0.1 to 0.15 mm in width. The tail is 0.35 to 0.4 mm long and 0.04 mm wide. 
At the posterior end the tail tapers to a blunt point. In view of the importance attached by Sandground 
and Bonne (1940) to the presence of fluted fins on the tail in the cercaria of E. lindoensis which they 
described, these were carefully looked for but were found wanting. 
The cuticle on both surfaces is covered, more noticeably in the anterior part, with fine spines which 
can only be seen with difficulty in unstained specimens. They become more evident after staining the 
cercariae lightly with methylene blue. 
The reniform cephalic collar (which is more prominent in fixed specimens) measures 0.07 to 0.1 mm 
across and carries 37 spines of approximately the same size arranged in two alternating rows. There is a 
corner group of 5 spines on each side. 
The mouth is subterminal but in preserved material appears terminal in position. The oral sucker 
measures 0.05 mm in diameter while the ventral sucker, which is behind the middle of the body, measures 
0.06 mm. The pharynx measures 0.026 mm long by 0.02 mm broad and is separated from the mouth 
by a short prepharynx. The oesophagus is 0.09 mm long and bifurcates in front of the ventral sucker 
into two simple intestinal caeca which extend to near the posterior end of the body. 
The excretory vesicle is rectangular with the antero-lateral comers and the centre of the posterior 
surface drawn out to receive the excretory canals. The main lateral canals are narrow from the bladder 
to the level of the ventral suckers after which they expand, and become more wavy and filled with numerous 
dark refractive granules. At the level of the collar they become narrower and free of granules and recurve 
and continue posteriorly to the end of the body where they again turn forwards. Beyond this level, the 
fine tubules could not be followed with any degree of certainty. A fine collecting vessel extends from the 
posterior end of the bladder to the tip of the tail giving off near the proximal part a pair of branches which 
run outwards to terminate at the sides of the tail. Several flame cells were observed but it was not possible 
to determine their full number and the pattern and flame cell formulae were not worked out. 
Echinostome Cercaria with 43 Collar Spines 
This cercaria is very similar to the one described above but can be easily distinguished by the collar 
spines which number 43 instead of 37 and the corner group is composed of 4 instead of 5 spines. This 
MALAYA , No. 26. 1953 
