4 
PACIFIC SCIENCE, Vol. IX, January, 1955 
is a mucous trap feeder, and S. zelandicus 
differs widely from it, still making consider- 
able use of its ciliary feeding mechanism. 
We may regard Vermetus novae -hollandiae of 
Yonge’s account (1932) as the most primitive 
known type of the Vermetidae (Fig. Id). It is 
entirely a ciliary feeder, which must have been 
the original mode of life of all the Vermetidae 
after their development of the attached posi- 
tion; it lives cemented to coral or to calcareous 
algae on the wave-beaten shore line of the 
Great Barrier Reef and the tropical Pacific. 
Its shell tube is stout and straight with the 
sculpture concealed by encrusting growth. 
The foot is short and plug-shaped and bears 
a broad, saucer-shaped, chitinous operculum, 
overlapping a good deal at the sides of the 
foot. The gill is very large, and the ciliary 
currents, especially of the lateral and frontal 
fields, are very powerful. The filaments are, 
however, primitively triangular in shape, and 
form the least modified type of gill among 
the ciliary feeders discussed by Yonge (1938). 
There is a large pedal gland extending back- 
wards from the haemocoele of the foot into 
the cavity of the head and trunk, below the 
buccal mass and alongside the oesophagus. 
The sole of the foot, which formed the orig- 
inal creeping surface, is now greatly reduced, 
forming a small triangular area immediately 
in front of the mouth. Mucus is discharged 
from the pedal gland upon this area of the 
foot through a duct opening immediatel iny 
front of the foot; its aperture is flanked by a 
pair of short, stout pedal tentacles, unciliated 
except for a groove along their mesial sides, 
by which mucous secretion is carried to their 
tips. So far as can be ascertained the mucus 
of the pedal gland has little or no connection 
with feeding in Vermetus novae -hollandiae — it 
appears to perform a role of cleansing the 
surface of the head and foot adjacent to the 
mouth and carrying away rejected particles. 
Within the mantle cavity, extending along 
the right side of the roof and the right side 
of the floor respectively, are two further mu- 
cous glands forming wide epithelial tracts. 
The first is the hypobranchial gland forming a 
normal part of the pallial equipment in all 
prosobranchs and apparently little concerned 
with feeding in Vermetus. The other forms a 
food tract by which collected food particles 
deposited by the gill on the right side of the 
pallial floor are swept forward by long cilia 
to the region of the mouth, where they are 
seized, in small mucous boluses, by the radula. 
Though powerfully ciliated, the gill fila- 
ments of Vermetus novae -hollandiae are other- 
wise little specialised, and it is probable that 
the Vermetidae first originated as ciliary feed- 
ers of a type like this species. In rough water 
on a wave-beaten shore ciliary feeding is ob- 
viously much more efficient than the use of 
mucous traps. Calm water and some amount 
of shelter are required, in order to allow the 
use of the pedal gland in feeding; which is 
done to some extent by almost all the remain- 
ing members of the family. In retaining the 
more primitive feeding mechanism of the 
family, Vermetus novae -hollandiae has remained 
well-adapted to life in rough water. 
Two relatively primitive genera of the Ver- 
metidae, which, like Vermetus novae -hollandiae, 
retain a fully developed operculum are the 
New Zealand Novastoa (Fig. lb) and the 
American Spiroglyphus. From the structure of 
the operculum, the radula, and the embryonic 
shell, these two genera are evidently very 
closely related (Morton, (1951c)). A similar 
level of evolution has evidently been reached 
by the American Petaloconchus which the 
writer has handled only as fixed material, and 
has not watched feed. In Novastoa lamellosa , 
which we may take as a stage of evolution 
next advanced upon Vermetus novae-hollandiae , 
the chief means of food collection is still by 
cilia, and this species frequents disturbed 
water where mucous traps would be liable to 
dislodgment (Cranwell and Moore, 1938). 
The filaments of the gill are triangular and 
rather unspecialised and the pallial cavity has 
a ciliated food tract along its right floor. Here, 
in addition, the pedal gland is a long, well- 
developed strap passing well backwards into 
