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Top
shell snails
Family Trochidae
updated
Aug 10
if you
learn only 3 things about them ...
 One
Family member is the very large Giant top shell.
The
tiny Button shell snail is a member of the Family too!
Many are threatened by over-collection. |
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Where
seen? These snails with top-shaped shells are commonly
seen on many of our rocky shores including man-made sea walls. Top
shell snails are not as well adapted to dry conditions as the Nerites
and Periwinkles, and are thus generally found closer to the low water
mark.
Features: 3-15cm. The thick shell
is shaped like a top. The operculum is circular with a clear spiral.
It is made of a thin, horn-like material and is flexible. This allows
the snail to withdraw deep into the coils of the shell, hopefully
out of the reach of crab pincers. The shell is sometimes covered in
encrusting lifeforms. In some species, the foot of the living animal
is fringed with long tentacles.
Sometimes confused with the Turban
snail (Family Turbinidae) which has a shell with more distinct
whorls and a thick, chalky operculum. While the Top snail has a more
pyramidal shell and a thin operculum made of a horn-like material.
Here's more on how to tell apart turban
and top shell snails.
What do they eat? Top shells graze the algae that thrive
on the rocks, scraping this off with their radula.
Human uses: The shell
is lined with mother-of-pearl. Larger species are collected for food
and their shells that are made into ornaments and pearl buttons. This
is still a significant industry in some Pacific Islands and effort
is being made to establish a susbtainable method of farming these
snails.
Status and threats: The Giant
top shell (Trochus niloticus) and Button
snails (Umbonium vestiarium) are listed as 'Vulnerable'
on the Red List of threatened animals of Singapore.
Like other creatures of the intertidal zone, the rest of our top shell
snails are affected by human activities such as reclamation and pollution.
Trampling by careless visitors and over-collection can also have an
impact on local populations.
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Family
Trochidae recorded for Singapore
from
Tan Siong Kiat and Henrietta P. M. Woo, 2010 Preliminary Checklist
of The Molluscs of Singapore.
in red are those listed among the threatened
animals of Singapore from Davison, G.W. H. and P. K. L. Ng
and Ho Hua Chew, 2008. The Singapore Red Data Book: Threatened plants
and animals of Singapore.
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Top
shells seen awaiting identification
Species are difficult to positively identify without
close examination.
On this website, they are grouped by external features for convenience
of display. |
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Chrysostoma
paradoxum
Clanculus granosus
Clanculus margaritarius
Ethminolia vitiliginea
Euchelus asper
Euchelus atratus
Euchelus quadricarinatus
Granata sulcifera
Hybochelus cancellatus
Minolia biangulosa
Minolia holdsworthana
Minolia singaporensis
Monilea callifera
Monilea lentiginosa
Monilea solanderi
Monodonta labio (Toothed top shell
snail)
Pagodatrochus variabilis
Pseudominolia musiva
Tectus pyramis
Thaliota zebuensis
Trochus maculatus (Spotted top
shell snail)
Trochus niloticus
(Giant top shell snail) (VU: Vulnerable)
Trochus radiatus
Trochus tentorium
Trochus tricatenatus
Turcica maculata
Umbonium vestiarium
(Button snail) (VU: Vulnerable) |
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| Links
References
- Tan Siong
Kiat and Henrietta P. M. Woo, 2010 Preliminary
Checklist of The Molluscs of Singapore (pdf), Raffles
Museum of Biodiversity Research, National University of Singapore.
- Tan, K. S.
& L. M. Chou, 2000. A
Guide to the Common Seashells of Singapore. Singapore
Science Centre. 160 pp.
- Wee Y.C.
and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore.
National Council on the Environment. 163pp.
- Davison,
G.W. H. and P. K. L. Ng and Ho Hua Chew, 2008. The Singapore
Red Data Book: Threatened plants and animals of Singapore.
Nature Society (Singapore). 285 pp.
- Abbott, R.
Tucker, 1991. Seashells
of South East Asia
 .
Graham Brash, Singapore. 145 pp.
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