CONTENTS
Flora index
Fauna index
guide to the mangroves of singapore
Molluscs
Peter K L Ng and N Sivasothi (editors)
 
Mangrove slugs
Family Onchidiidae


There are more than 15 species in several genera of shell-less mangrove slugs all over Singapore mangroves, burrowing in the mud, on the forest floor, under wood and even climbing trees!

Species identification is difficult, requiring an examination of the texture and features on the dorsal and ventral surface, and even the arrangement of internal organs! Hence they are often referred to collectively as 'Onchs' - which means lump! (Onchidium is the Latinised derivation of the Greek word for 'little lump'!).

close-up of underside
Ventral surface:
the centre is the foot.
It is usually narrow in
Platyvindex sp.

close-up of under and upperside
Onchidium griseum
has an orange margin
on the ventral surface

close-up of underside
Onchidium nigram
has a yellowish
orange foot (above)
and black specks
around the foot (below)
magnified close-up of foot
close-up of onch on mud
Paraonchidium sp.

group of onchs on sand
Paraonchidium
is a gregarious species
(length 1.5 cm)

wide shot of sand bank with onchs
Paraonchidium sp.
(the smaller specks on
the sandback surface)
emerge from the
burrows to feed
Like the ellobiid snails, 'Onchs' are hermaphrodites, with a complicated system of ducts, glands and sacs to ensure cross- but not self-fertilisation.

Most species probably graze on detritus and surface algae.
The most common species in our mangroves is Onchidium aberrans, and many of the tree-climbers are species of Platyvindex.

Paraonchidium sp. is a small, burrowing species and may occur in densities of up to 200 individuals per square metre on some patches of muddy sand during low tides. Being air-breathers, they burrow to form S-shaped tubes, forming an air pocket from which they breathe during immersion. On sandy banks smoothened by the receeding tide, they create a spectacular sight of churned sand as they emerge from their burrows to graze above ground.

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What is mangrove?
Introduction

The Ecosystem

Abiotic
Biotic

Value
Intro
Products
Indirect uses
Potential uses

About Mangroves
in Singapore

History
Mangroves to visit
Conservation
 
From "A Guide to Mangroves of Singapore", Peter K. L. Ng and N. Sivasothi (editors)
Volume 1: The Ecosystem and Plant Diversity and Volume 2: Animal Diversity
Authors: Kelvin K. P. Lim, Dennis H. Murphy, T. Morgany, N. Sivasothi, Peter K. L. Ng,
B. C. Soong, Hugh T. W. Tan, K. S. Tan & T. K. Tan
BP Guide to Nature Series published by the Singapore Science Centre, sponsored by British Petroleum
2001 Raffles Museum of Biodiversity Research, The National University of Singapore & The Singapore Science Centre