Growth of Arachnoides placenta — Hines and Kenny 
233 
ff 
I 
I 
« 
I 
I 
I 
/ 5 ““* 
Fig. 3. Growth curve for A. placenta related to sea water temperatures at Townsville. 
(1934), where size and test thickness distin- 
guished an "inshore race’’ of Echinus escu- 
lentus. 
Direct comparison of the growth rate of A. 
placenta with the results of growth studies on 
other echinoids is difficult because of marked 
species differences in size and shape. In Table 2 
the increase in size per annum is expressed as 
a percentage of the diameter for the preceding 
year for selected species. The data for Mellita 
are possibly those most relevant, inasmuch as 
this species is similar in shape to Arachnoides 
in contrast to the spherical form of the other 
species listed. 
TABLE 2 
Comparison of Growth Rates of Selected Echinoids 
PERCENTAGE INCREASE IN D T AMETER 
YEAR 
Echinus 
( Moore, 
1935) 
Psam- 
mechinus 
(Bull, 
1938) 
Strongy- 
locentrotus 
(Norway) 
(Greig, 
1928* ) 
2 
36 
30 
150 
3 
12 
12 
60 
4 
10 
3 
33 
5 
14 
23 
25 
6 
5 
20 
Strongy- 
locentroius 
(Maine) 
Mellita 
(Swan, 
( Crozier, 
1958) 
1920) 
Arachnoides 
176 
30 
22 
68 
14 
19 
25 
43 
Quoted by Hyman (1955). 
