18
R. H. MILLAR
1.63 140 )
0
a* 1.2,a 1.0.
: 0.8B
fl
-- 0 . 8 -
c
r A
W
W
m
0.21.3 mm (Millar, 1962b), Eudistom fantasianum at 1.5 mm (Kott,
1957a)) Polyeitor circes a t 2.5 mm (Millar, 1963)) Hypsistozoa fmmeriana
at 2.5 mm (Brewin, 1956a, 1950) and Eudistomdigitatum at 4 4 - 4 6 inm
(Millar, 1964s).
The functional significance of larval structure has been interpreted
by Berrill (1955) in relation to the choice of a suitable site for adult life.
Within the order Enterogona the large solitary forms live in places
whcrc their small simple larva is adequate for site choice, but the compound forms have a more specialized habitat requiring a larger more
efficient larva. Berrill traces a similar correspondence betwcen larval
type and adult habitat through the families of the order Pleurogona. In
particular the family Molgulidae shows an adaptive loss of the larval
ocellus, for many molgulids live on sublittoral sand and mud, where
larval reactions to changes in light intensity (shadow reflex) are unimportant or definitely disadvantageous. A further step has been taken
by a number of the sand-dwelling molgulid species, by elimination of
the larval stage, and the same adaptation has arisen independently in
response to similar habitat requirements in the styelids Pelonaia
corrugata Forbes and Goodsir (Millar, 1954a) and Polycarpa tinetor
(Quoy and Gaimard) (Millar, 1962a).
2.0
1
I
1
0!2 0!4
0!6
0!8
l!O
112
114
l!6
1.8
2.0
2.2
I
I
Tail length, m m
FIG. 6. Swimming sped in relation to size of larva (from data in Berrill, 1931).
R. H. MILLAR
1.63 140 )
0
a* 1.2,a 1.0.
: 0.8B
fl
-- 0 . 8 -
c
r A
W
W
m
0.21.3 mm (Millar, 1962b), Eudistom fantasianum at 1.5 mm (Kott,
1957a)) Polyeitor circes a t 2.5 mm (Millar, 1963)) Hypsistozoa fmmeriana
at 2.5 mm (Brewin, 1956a, 1950) and Eudistomdigitatum at 4 4 - 4 6 inm
(Millar, 1964s).
The functional significance of larval structure has been interpreted
by Berrill (1955) in relation to the choice of a suitable site for adult life.
Within the order Enterogona the large solitary forms live in places
whcrc their small simple larva is adequate for site choice, but the compound forms have a more specialized habitat requiring a larger more
efficient larva. Berrill traces a similar correspondence betwcen larval
type and adult habitat through the families of the order Pleurogona. In
particular the family Molgulidae shows an adaptive loss of the larval
ocellus, for many molgulids live on sublittoral sand and mud, where
larval reactions to changes in light intensity (shadow reflex) are unimportant or definitely disadvantageous. A further step has been taken
by a number of the sand-dwelling molgulid species, by elimination of
the larval stage, and the same adaptation has arisen independently in
response to similar habitat requirements in the styelids Pelonaia
corrugata Forbes and Goodsir (Millar, 1954a) and Polycarpa tinetor
(Quoy and Gaimard) (Millar, 1962a).
2.0
1
I
1
0!2 0!4
0!6
0!8
l!O
112
114
l!6
1.8
2.0
2.2
I
I
Tail length, m m
FIG. 6. Swimming sped in relation to size of larva (from data in Berrill, 1931).