418 
5mm 
Fig. 2. Ventral view of head of macrophthalmia of 
Mordacia mordax. 
the two species, another striking difference be- 
tween them is the more posterior position of 
the cloacal aperture in M. mordax. This is ex- 
pressible in relation to the total length of the 
body, in relation to the anterior border of the 
second dorsal fin, or in the number of precloacal 
myomeres. 
COMPARISON OF AMMOCOETES OF 
G. australis AND M. mordax 
It was possible that the Mordacia macroph- 
thalmia had been accidentally included in a 
PACIFIC SCIENCE, Vol. XIV, October I960 
sample of Geotria ammocoetes, but examination 
of these showed that in the position of the cloaca 
they closely resembled the Mordacia specimen 
and differed from known ammocoetes of Geotria 
(Table 2). Dissection of several of the ammo- 
coetes revealed that each possessed only one 
intestinal diverticulum, thus confirming Has- 
kells original observation. Figure IB shows the 
body proportions of an ammocoete 123 mm. 
long. 
DISCUSSION 
It is unfortunate that the sample of Mordacia 
ammocoetes contained no smaller specimens 
which could be compared with small specimens 
of Geotria. However, the great uniformity in 
proportions over the length range, 100-160 mm., 
suggests that smaller ammocoetes of Af. mordax 
would also be distinguishable by the position of 
the cloaca. In adult specimens of Mordacia the 
cloaca is found at 83-84 per cent of the length 
of the body, there being no difference in this 
respect between M. mordax, M. lapicida , or M. 
acutidens specimens in the British Museum. In 
the velasia stage of G. australis the cloaca 
occupies almost the same position as in the 
macrophthalmia and the ammocoete. Eleven 
unpouched specimens had the cloaca at 77 ± 
1 per cent of the total length. However, the 
resorption of the tail tissues, consequent upon 
the cessation of feeding in the adults, causes a 
relative backward shift in the position of the 
cloaca and the first dorsal fin. In 11 pouched 
adults, these occurred at 79 zb 3 per cent of the 
total length. 
TABLE 1 
Comparison of Macrophthalmia Stages of Mordacia mordax and Geotria australis , Based on One 
Specimen of M. mordax and Six Specimens of G. australis 
(Standard deviations calculated for all means) 
M. mordax 
G. australis 
Total length (T. L. ) 
122 mm. 
57% of T. L. 
72% of T. L. 
83% of T.L. 
102 
two, each with 3 cusps 
absent 
absent* 
103 ± 5 mm. 
58 ± 1% of T.L. 
76 ± 1% of T.L. 
76 ± 1% of T.L. 
93 ± 2 
one, with 4 cusps 
present 
present 
Tip of head to origin of first dorsal fin 
Tip of head to origin of second dorsal fin 
Tip of head to anterior border of cloaca 
Number of precloacal myomeres 
Supraoral lamina 
Pair of enlarged lateral buccal cirri 
Coloured dorsal stripes 
* The skin of this specimen is very similar to that of an ammocoete, having no metallic lustre. It is possible that the speci- 
men is incompletely metamorphosed in this respect or that the specimen became decolourized by preservation. 
