20
Snails: Friend or Foe in the Aquarium?
By Richard Brown
(Article previously published in Tank Talk)
Introduction
Snails have a bad reputation. When I first started keeping fish around 12 years
ago, I was told by many ?reliable‘ sources that snails were bad news: "They will
eat your plants," "they will breed like crazy and turn your tank into a creeping
mass of snails," "they will foul your water." Not surprisingly, for several years I
have treated snails with an amount of disgust and contempt. However, over the
last few years I have discovered that snails are actually a very useful and
decorative creature. I hope the following account will encourage some of you to
give snails a go.
The Biology of Snails
Along with creatures such as Clams and Oysters, snails belong to the phylum
Mollusca. A generalised trait of molluscs is that they are soft-bodied creatures
lacking supporting structures such as bones or exoskeletons. The topic of this
article, snails, belong to the class Gastropoda. Gastropods are distinguished by
their having a single shell. This shell is usually coiled and is part of the snail's
living body. The soft-bodied section of the snail can be withdrawn into the shell,
thus forming a defence against predators.
An important thing to know about snails is that they have been on this planet
probably longer than us, the primates, and our pets, the fish, combined. Snails
appear in the fossil record around 500 million years ago. They are easy to find
around many of the limestone cliffs on the Australian coast.
Snails are a very successful species, there are around 80,000 species of snails
that have been identified. The majority of snails, approximately 55,000, can be
found in the marine environment. The remainders are land snails and freshwater
snails. Water snails breathe through gills whereas land snails breathe through a
hole in their body near the base of the shell.
Land snails are hermaphroditic, that is, each snail has both male and female
parts. They still must mate to reproduce, however. A hole near the head is the
genital orifice where the snail mates and also from where it lays its eggs. Aquatic
snails have both hermaphroditic and heterosexual reproduction. Most snails lay
eggs, however a notable exception to this is the Malaysian Trumpet Snail, which
is a live-bearer.