Vermetid Gastropods — Morton 
7 
certainly in Spiroglyphus , the egg capsules re- 
main unattached, lying freely within the man- 
tle cavity. But in the nonoperculate forms 
which retreat quickly into narrower parts of 
the shell, egg capsules so retained would be 
liable to damage during the rapid withdrawal 
of the head and foot into the mantle cavity 
as the animal darts into the shell. By means 
of the pallial slit a row of three or four egg 
capsules can be attached directly to the inner 
surface of the shell by short stalks. On the 
retreat of the animal, the capsules remain 
attached near the mouth of the shell; as the 
animal again expands the mantle wall extends 
forward around them. 
The genus Bivonia , of which the Mediter- 
ranean species triqueter is the best known ex- 
ample, appears to have reached the Serpulorbis 
zelandicus stage of evolution. The operculum 
however remains as a small button-like vestige 
upon the terminal disc of the foot. The shell 
is long, irregular, and vermiform, and the 
animal retreats deeply and has a slit mantle 
in the female. According to Yonge (1932), 
mucous traps are formed by the pedal gland, 
but in addition the gill remains well-developed. 
The most advanced group of Vermetidae, 
in feeding habits, is probably that typified by 
Serpulorbis gigas, whose feeding mechanism 
has been described in great detail by Boettger, 
and Aletes squamigerus , of which the McGinities 
(1949) have given an account. There is also 
a brief general description of the feeding 
habits of the latter and a good figure in 
Ricketts and Calvin (1948). In both these 
species mucous traps have entirely replaced 
the cilia of the pallial cavity in feeding. The 
gill is very small and insignificant, and the 
ciliary tracts and glandular region of the pallial 
floor much reduced in importance. No doubt 
strong inhalant and exhalant currents, if pres- 
ent at the opening of the mantle cavity, would 
impede the full employment of mucous traps. 
In Serpulorbis gigas , mucous strings are ex- 
truded, which reach 8 or 9 inches in length, 
i.e. several times the average length of the 
animal. These are waved about gently with 
the slight movements of the surrounding 
water and presently withdrawn and ingested 
with the food particles that have become at- 
tached to them. It is claimed by Boettger 
that S. gigas captures small zooplankton in 
this way, and in one case, the presence in the 
stomach of numerous small shells of gastro- 
pods (possibly veliger larvae?) was reported. 
Yonge (1932) maintained that the crystalline 
style and gastric shield were lost, with the 
abandonment of ciliary feeding. Later Yonge 
and lies (1939) reported the presence of a 
small gastric shield of greatly reduced extent. 
A dissection of fixed Serpulorbis gigas by the 
present writer reveals a style sac and gastric 
shield of similar proportions to that of Ser- 
pulorbis zelandicus; in Aletes , too, the stomach 
has its normal structure with a prominent 
style sac and shield. The loss or reduction of 
the crystalline style is thus evidently not an 
accompaniment of this type of mucous feed- 
ing in vermetids, and the mode of action of 
the stomach conforms to that of style-bearing 
prosobranchs in general, as discussed by 
Morton (1952). 
In Aletes squamigerus , (Fig. Id) the reduction 
of the gill has been accompanied by great 
development of the pedal gland as in Ser- 
pulorbis gigas, but here, instead of the forma- 
tion of long separate strings, the extruded 
mucus takes on the form of a continuous 
sheet and feeding becomes the combined ac- 
tivity of a large cluster of gregarious indi- 
viduals. As described by the McGinities 
(1949), "When the animals occur in clusters, 
the fan-shaped sheets of mucus they put out 
become entangled, and the table with its bill 
of fare becomes a community affair. When 
one member in such a group begins to eat 
the mucus sheet, all the others start swallow- 
ing. The sheets of mucus may extend upward 
into the water for five or six inches/’ 
The demarcation of genera in the Aletes- 
Serpulorbis series is at present a very uncertain 
proceeding. There would appear to be no 
well-marked conchological characters to dis- 
criminate between forms such as Serpulorbis 
