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Drills
Family Muricidae
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Thais clavigera
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You will almost be certain to meet this ferocious predator on the
rocks of Chek Jawa!
Bored to Death: Drills that live
on the rocks are predatory molluscs that bore into other shelled creatures,
especially barnacles. To bore a hole through the victim's shell, a
drill softens the shell with an acid secreted by a special gland on
the underside of its foot. A hole is slowly created with a little
help from its radula. It can take eight hours for a drill to get through
a shell 2mm thick. Yawn!
Other Drill food and feeding methods:
Some drills may also pry open clam shells with a tooth on the lip
of their shell. Others may also get to limpets by inserting their
proboscis under the limpet's shell. Some may also hunt buried clams.
Some prey on oysters, limpets, worms, the eggs of other snails and
even corals. Some deeper-water members of the Family Muricidae eat
worms and sea urchins.
Among the common drill species on Chek Jawa are Rock-shell (Thais
sp.), Drupes (Morula sp.) and Murex (Chicoreus sp.).
Drills
usually have thick shells and a thick operculum made of a horn-like
material.
To dye for: Many Drills have a
gland that secretes a colourless mucus that turns purplish when exposed
to air. This secretion is a neurotoxin that paralyses or kills other
sea creatures. Humans have used this mucus as a rare dye (see below).
Drill Babies: Some drills lay
masses of bright yellow egg capsules. Each egg capsule may contain
20-40 eggs. The egg capsules turn purple when the free-swimming larvae
hatch. These swim about for a few weeks before they change into crawling
juveniles. In some, however, crawling juveniles emerge from the egg
capsules.
Human uses: Since 1,500 BC in
the Mediterranean, snails of the Family Muricidae were harvested to
produce a dye called Tyrian purple (which was actually more maroon).
The dye resisted fading, but involved so much labour to produce that
only royalty and the rich could afford it. Thousands of shells were
crushed to obtain minute quantities of the dye. The dye was worth
several times its weight in gold. The dye industry brought fame and
fortune to Tyre (now modern Lebanon). Tyre was a great Phoenician
city. In fact Phoenicia means "purple people". Tyre ruled
the seas and founded prosperous colonies such as Cadiz and Carthage.
The prosperity of Tyre allowed the arts and sciences to flourish.
For example, Marinus of Tyre was considered the founder of mathematical
geography and introduced the concept of latitude and longitude in
map design. As merchants who needed to keep records, the Phoenicians
simplified the 550 characters in the cuneiform alphabet with a phonetic
alphabet, based on distinct sounds, consisting of 22 alphabets. This
alphabet, with modifications introduced by the Greeks and Romans,
is the one we use today.
Some Drills are now considered a menace to oyster farms. Drills may
be used as a bio-indicator of the toxins used to paint ship hulls
to prevent barnacles from settling on them. The toxins kill Drill
larvae, or result in deformities in adults. |
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Thais gradata
Drills laying
egg capsules
Egg capsules can look quite pretty!
Attacking a bivalve
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quick
facts
2-3cm, common on the rocky shore
Classification:
Class Gastropoda
Phylum Mollusca |
