Moon snails belong to a family of gastropod molluscs
called the Naticidae or moon snails. This group is characterised by
large rounded or globose shells and large bodies (the body tissue of
molluscs is referred to as the mantle). The last whorl of the moon
shell is very large making up around 85% of the entire shell. The entrance
to the shell of living specimens is covered by a chitinous operculum
(The operculum is the “door” that enables the shell to
be sealed thus protecting the snail from predation). When the animal
active the mantle will cover a large percentage of the shell. On the
rare occasions that you observe this species above the sand, which
is usually when it is in hunting mode, you can observe a thickening
body tissue at the front of the animal. This acts like the blade of
a plough, pushing sand out of the way of the animal. The relatively
food of the snail acts like a snowshoe, spreading its weight and allowing
for relatively fast movement across a treacherous substrate. This is
also aided by the production of copious amounts of mucus that binds
the sand together leaning that the animal is less likely to sink beneath
It is incredible to observe a moon snail unpacking its massive body
from inside the relatively small shell but it can do it. It’s
like watching a driver’s airbag inflating in slow motion. The
snail is unlikely to remain in a closed state for too long as it is
known to have extreme difficulty in breathing when packed inside its
shell and it is far more reluctant to shut itself away in the first
place preferring to wait for extreme emergencies before it takes evasive
action. Once the snail is out it can then bury itself in the substrate-the
environment of choice for the Naticidae, something that it can achieve
in a very short period of time. Even large specimens can be completely
concealed beneath the substrate in less than a minute. So the fact
that you are not going to see much of this beautiful snail in you aquarium
is one good reason not to purchase it. However, take a look at the
diet of this species and you will have several more.
Moon snails are carnivorous and their range of prey items is such
that they will preclude their inclusion in most reef aquaria. The
Naticidae are renowned for their predation of bivalve molluscs and
to the tropical reef aquarist that means flame scallops and Tridacna
or Hippopus clams. Their style of attack depends upon the size and
species of prey item involved. Large clams are often literally undermined
by the snail: the snail excavates the substrate from beneath the
clam causing the bivalve to fall into the void space. It then becomes
smothered by sand and suffocates realizing its large adductor muscles
that are responsible for keeping the shell closed. The moon snail
can then feed at its leisure without once venturing above the surface
of the substrate.
If the victim is not susceptible to mining then the snail might try
using its specialized feeding apparatus, the radula, to bore a
hole into the hinge of the clam. This structure is located at the
of a long and flexible proboscis that secretes chemicals to aid
in the drilling process. Once the hinge has been broken the snail
gain access to the fleshy interior, which it macerates with the
radula and uses digestive secretions to break down before sucking
contents. Both of these strategies are generally employed in situations
where the victim is significantly large than the snail. The drill-hole
of a moon snail is quite characteristic being described as “funnel-shaped” by
many authors and is wider at the top than the bottom.
Smaller prey items are treated differently despite having thinner
shells that would be easier to penetrate by drilling. The moon
snail will use its large foot to grip and smother its victim. Aquarists
without any bivalve molluscs in their aquaria should not necessarily
feel confident that their aquarium could be home to a moon snail.
Captive specimens have been observed feeding upon Nassarius snails
using the foot-hold-and-suffocate technique and it would be prudent
not to introduce moon snails to an aquarium containing any species
of mollusc including the various herbivorous gastropods collecting
known as “turbos”.
Many species of moon snail are reported to supplement their shellfish
diet with scavenging upon the corpses of fish or invertebrates. In
captivity the acceptance of whole dead cockles, mussels or pieces of
fish seems to depend upon the individual concerned. If an aquarist
envisages a role for this species, for example in an isolated deep
sand bed where it will turn over the sand and prevent it from becoming
compacted then it would be wise to observe a specimen feeding on dead
material before introducing it to the aquarium. As is often the case
with species that are largely unsuitable for most marine aquaria the
white moon snail has so wonderful characteristics that would immediately
endear it to aquarists and not least amongst these is the production
of “sand collars”.
There will be a small number of aquarists out there that have bought
white moon snail for their advertised sand shifting abilities. A number
of these individuals will have awoken one morning and gone for their
morning aquarium inspection to be greeted by a bizarre structure arising
from their sand. This is a sand collar and despite resembling a medieval
ruff crafted by a highly skilled artisan from fine grains of sand it
is in fact the egg mass of the white moon snail. Even when armed with
this knowledge close scrutiny of the structure does not help to explain
how the snail is capable of creating such a delicate structure. Each
layer is very thin and delicate and yet the entire structure seems
to be quite durable; withstanding strong flow and the boisterous behaviour
of fish. This is because the entire construction is held together by
First of all the snail cements a ribbon of sand together by exuding
mucus from the underside of its broad foot. It then deposits a thin
layer of eggs on top of this that is sandwiched by another layer of
sand and so on. All the time this process is going on the snail moves
in a circular manner creating the characteristic multilayered structure.
This behavior seems to have been elaborated from the production of
egg masses within a gelatinous cocoon made entirely from mucous. Some
members of the Family Naticidae still produce these to protect their
eggs. Other species in the group produce much simpler sand collars
than the white moon snail consisting of a single whorl, sometimes not
even creating a complete circle.
On average the moon snail will deposit around 100,000 – 500,000
eggs when fully grown. These will stay in the sand collar for approximately
2-6 weeks depending upon thespecies. When the eggs the larvae are planktonic
and therefore will not survive for long but may give some corals and
other invertebrates a good feeding before they are taken care of by
the aquarium filtration. Ironically, the veliger larvae of the moon
snail are exactly the type of zooplankton that is filtered out of the
water column by bivalve molluscs.
At the present time the hobby is only having what might be called a
brief flirtation with the moon snails and Polinices tumidus is the
only species being imported with any regularity. Some species have
been reported as being the size of an apple with an appetite to match.
Adult Naticidae have been shown to consume around one bivalve
every four days on average which means that most would make short work
an aquarists clam collection in a very short period of time!
Moon snails are unlikely to be confused with many other mollusc families
but the most similar group are a small group of primitive opistobranchs
that have retained their shells and are commonly know as bubble snails.
It is thought that they represent a “missing” link between
the relatively sophisticated shell-less sea slugs and the shelled
mollusc. There are a number of characteristics of each that the aquarist
use to separate these two families.
Hydatina albocincta is an opistobranch mollusc that is superficially
similar to the moon snail family. The enlarged foot surrounds the
The large foot of the moon snails is mirrored in the Hydatinidae yet
in the latter it is far more elaborate having curled edges and seemingly
indulgent folds. However, this is designed for creeping along the surface
of sandy substrates not for digging. The opistobranch does not need
a plough or shovel with which to bury itself. A second distinguishing
characteristic is the shell itself. It is difficult to ascertain why
Hydatina spp retain the shells as it is of sufficiently insubstantial
structure not to deter many predators. It could be that the brightly
coloured foot advertises that these molluscs are distasteful or even
toxic, a trait they would share with the moon snails that are known
to contain amounts of tetrodotoxin (this is the same potentially lethal
poison found in some species of pufferfish) but nonetheless it is possible
to discern significant differences between the shell of the moon snails
and that of the Hydatindidae.
Contain Toxic TTX Tetrodotoxin-same toxin found in pufferfish.
Volume 70 Issue 6 Page 1106 - December 2004
Neurotoxin tetrodotoxin as attractant for toxic snails
PAI-AN HWANG1, TAMAO NOGUCHI1 AND DENG-FWU HWANG1*
Ecology: Vol. 58, No. 6, pp. 1218–1236.
Feeding and Growth Rates of Polinices Duplicatus Preying on Mya arenaria
at Barnstable Harbor, Massachusetts
Kingsley-Smith, P. R., Richardson, C.A. & Seed, R. 2003.
Stereotypic and size-selective predation in Polinices pulchellus (Gastropoda:
Naticidae) Risso 1826. Journal of Experimental Marine Biology and Ecology,
Kingsley-Smith, P. R., Richardson, C. A. & Seed, R. (2005). Growth
and development of the veliger larvae and juveniles of Polinices pulchellus
(Gastropoda: Naticidae). Journal of the Marine Biological Association
of the UK. Vol. 85, pp. 171-174.
Kingsley-Smith, P. R., Richardson, C. A. and Seed, R. (2003). Seasonal
and size-related egg collar production by Polinices pulchellus (Gastropoda:
Naticidae) Risso 1826. Journal of Experimental Marine Biology and Ecology.
Vol. 295, pp. 191-206.
Kingsley-Smith, P. (2003). Polinices pulchellus: The James Dean of
gastropods: Living fast, dying young. Journal of Shellfish Research.
Vol. 22, p. 337.