6 
PACIFIC SCIENCE, Vol. IX, January, 1955 
the haemocoele of the trunk. Fairly constant- 
ly, while the animal is feeding, the gland 
extrudes a small triangular or conical mass of 
mucus which hangs indecisively over the 
edge of the foot. The mucous gland of the 
foot is here evidently beginning to develop 
a feeding as well as a cleansing function; but 
although the animals were watched during a 
long period of feeding by the aid of water 
goggles, the mucous traps with their col- 
lected particles were never seen to be ingested 
and the disturbance of the water surface by 
wave action often impeded their proper for- 
mation. 
The gill in the Vermetidae never becomes 
more specialised than at the Vermetus-Novastoa 
level; on the contrary two other trends have 
begun to appear, to a greater or lesser extent, 
in all the other members of the family: a loss 
of reliance on the pallial organs in feeding, 
and the exploiting of the pedal mucous gland, 
which in every member of the family is al- 
ready prominently developed. 
Serpulorbis zelandicus (Fig. 1 c) is probably 
typical of the Vermetidae which are beginning 
to undertake mucous feeding. This species 
undoubtedly uses the gill in feeding to a 
major extent (Morton, 195 1^) and also puts 
out long slender mucous strings from the 
pedal gland, which are evidently drawn in by 
the pedal tentacles or the radula, and ingested 
after they have become loaded with micro- 
scopic particles. The pedal gland is very stout 
in Serpulorbis zelandicus , much more so than 
in Vermetus novae -hollandiae or Novastoa lamel- 
losa (where it is still relatively narrow) and 
more nearly resembles in extent that of Ser- 
pulorbis gigas. The ciliary feeding mechanism 
of the pallial cavity has, however, undergone 
hardly any reduction as yet; the gill filaments 
are large and triangular and prominently 
ciliated, and although, as is always the case 
in Vermetidae, there is no glandular "endo- 
style” running along the gill axis the ciliated 
and mucus-producing food tract is strongly 
developed. The cross-section (Fig. 3) across 
the trunk and pallial cavity illustrates the lo- 
cation of the glandular tracts; the hypobran- 
chial gland is well-developed too, although it 
plays little part in supplying mucus for food 
collecting. 
The serpulorbids have two further modi- 
fications which can be regarded as being asso- 
ciated with the feeding adaptations. First, the 
operculum is entirely lost and the terminal 
disc of the foot is naked and generally bright 
coloured. Its edge is very thin and mobile and 
may easily be indented or retracted at any 
point so that the formation of mucous strings 
and their employment is not impeded, as 
would be the case in the presence of the rigid 
edge of a projecting operculum. The sole of 
the foot is also very small in Serpulorbis , and 
relatively much less conspicuous than in Ver- 
metus novae -hollandiae or Novastoa lamellosa. 
The loss of the operculum makes necessary 
the power of quick retreat into the shell; and 
this is probably correlated in turn with the 
tendency of the shell in Serpulorbis, Aletes, and 
Bivonia to become long and vermiform, of 
far greater length than is normally occupied 
by the animal. However, other factors no 
doubt enter into the determining of shell 
form, or lack of it, in vermetids; thus in genera 
such as Novastoa and Spiro glyphus which do not 
retreat deeply, but rely on large opercula, the 
shell also tends to become elongated. More- 
over, in some of the species of Serpulorbis the 
deeper parts of the shell are cut off by septa. 
The length of the visceral mass also increases 
in the species of Serpulorbis , whereas in Ver- 
metus and in many specimens of Novastoa 
lamellosa the visceral mass, including the pos- 
terior lobe of the digestive gland, is rather 
short and blunt. 
A related adaptive trend in the evolution 
of the Vermetidae is the development of a 
long median slit in the mantle of the female; 
this is associated with the protection of the 
eggs, which in all genera of the family are 
retained in capsules within the mantle cavity 
until the emergence of the crawling benthic 
embryo with its regular spiral shell. In Nova- 
stoa, Petaloconchus, and Vermetus, and almost 
