A Comparison of the Ammocoete and Macrophthalmia Stages of 
Mordacia mordax and Geotria australis (Petromyzonidae) 
R. Strahan 1 
Very little is known of the biology of 
the lampreys of the Southern Hemisphere. On 
the available evidence (Strahan, 1959), there 
appears to be only one species of Geotria, G. 
australis Gray 1851, extending from Western 
Australia eastwards to the Falkland Islands. Al- 
most nothing is known of its distribution while 
in the marine stage of its life history. The 
northern limits of its distribution in estuaries 
and rivers appear to be 32° S. on the west coast 
of Australia and 37° S. on the east coast of Aus- 
tralia and the North Island of New Zealand; 
40° S. on the west coast of South America and 
35° S. on the east coast. It extends southwards to 
Tasmania, the South Island of New Zealand, and 
Tierra del Fuego. 
Three species of Mordacia have been de- 
scribed. M. mordax (Richards) 1846 has a 
north-south distribution similar to that of Geo- 
tria australis but is restricted to the Pacific 
coasts of Australia ( where it extends northwards 
to about 34° S.) and of South America. The 
other two species, Mordacia lapicida (Gray) 
1851 and M. acutidens (Philippi) 1863, are 
apparently restricted to the Pacific coast of South 
America (Plate, 1902; Lahille, 1915; Holly, 
1933; Mann, 1954). 
In the course of the past century, Geotria 
australis was divided into as many as seven 
genera and nine species. This seems to have 
been due partly to enthusiastic "splitting,” but 
more to ignorance of the life history of the 
species, which is now known to comprise well- 
marked ammocoete, "macrophthalmia,” "vela- 
sia,” and adult stages ( Masked, 1929; Strahan, 
1959). In the almost complete absence of in- 
formation on the life history of any species of 
Mordacia, the possibility arises that a similar 
confusion exists here. Mann (1954) has sug- 
gested that the Chilean forms described as Mor- 
' Department of Zoology, University of Hong Kong, 
Hong Kong. Manuscript received April 16, 1959. 
dacia are the late developmental stages of 
Geotria, but this is unlikely since the dentition 
of Mordacia is very characteristic, it being the 
only lamprey with two supraoral laminae on the 
buccal funnel. Certainly the situation cannot be 
clarified until more is known of the development 
of Mordacia. 
Masked ( 1932 ) stated that the ammocoete 
of Mordacia has one intestinal ( exocrine pan- 
creatic ) diverticulum on the left side of the 
oesophagus, and can thereby be distinguished 
from the ammocoete of Geotria, which has both 
right and left diverticula, and from the ammo- 
coete of Petromyzon, which has no diverticula. 
However, the question arises : How did Masked 
know that the ammocoetes with only one diver- 
ticulum were referable to Mordacia? The only 
author to comment upon the external ap- 
pearance of Mordacia ammocoetes was Ogilby 
(1896), who stated that the dorsal and caudal 
fins are continuous in the ammocoete but sepa- 
rate in the adult. This is also characteristic of 
Geotria. Some of Masked’s Mordacia ammo- 
coetes were obtained from the Australian 
Museum, Sydney, N.S.W. Since they were dem- 
onstrably not Geotria, they could have belonged 
only to M. mordax or, rather improbably, to 
some undescribed Australian lamprey. Others 
were obtained from the British Museum (Nat- 
ural History ) , London, and their place of col- 
lection is not recorded. It is probably fortuitous 
that these were correctly identified. Conclusive 
proof of identity depends upon establishing a 
series of intermediate stages between the am- 
mocoete and identifiable postmetamorphic in- 
dividuals. 
DESCRIPTION OF MACROPHTHALMIA OF 
M. mordax 
The author had the good fortune recently, 
while revising the British Museum collection of 
lampreys from the Southern Hemisphere, to find 
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