learn only 3 things about them ...
hares may secrete a purple dye. But don't tease them to
make them do this.
they can be quite large, they are well camouflaged. Watch
Sea hares have very specialised diets and should not be
kept in home aquariums.
Among the largest sea slugs to be seen,
sea hares may be commonly seen on our Northern and Southern shores
in silty and sandy areas near seagrasses and with seaweeds. However,
they appear to be seasonal. Sometimes they are everywhere, at other
times, none are to be seen.
What are sea hares? Sea hares
are molluscs. They belong to Phylum Mollusca
and Class Gastropoda like snails.
Like many other sea slugs (Subclass Opistobranchia),
sea hares lack external shells as adults. Sea hares belong to Order
Anaspidea and are NOT nudibranchs,
which belong to a different Order Nudibranchia.
Features: Sea hares have two pairs
of tentacles. The front pair (called oral tentacles) are next to the
mouth and usually large and fleshy, sometimes with flaps. The second
pair (called rhinophores) is further behind on top of the 'head' and
usually smaller. The tentacles are made up of rolled tubes containing
chemical sensors. Some have tiny simple eyes at the base of the rhinophores.
Sea hares have a pair of 'wings' or flaps (called parapodia) that
cover the centre part of the body. Some sea hares can swim by flapping
Like other gastropods, most sea hares have a shell, but this is reduced,
thin and just under the skin. These internal shells may be made of
calcium or a horn-like material. Some sea hares lack internal shells.
The shell encloses the gills and the heart. The body wall (called
the mantle) has openings or a siphon to pump water in and out over
Sea hares can be quite large with reports of animals elsewhere reaching
60cm long and weighing 5kgs!
Sometimes confused with other
sea slugs that appear similar but belong to different orders. Here's
more on how to tell apart sea hares
from other sea slugs.
You are what you eat: Sea hares
eat seaweed and algae. They often match their food, in colour and
sometimes, texture as well!
Why are they called hares? It's
not really certain, but sea hares do move rather quickly, for a slug!
With some imagination, the tentacles on their head do resemble the
ears of a rabbit. Also, they are herbivores, eating seaweed.
Hare dye: Some sea hares produce
a purple dye when disturbed. The function of this dye is not known.
Unlike an octopus or squid, it doesn't form a screen for a quick escape
as most of these slugs usually don't move very fast. One
study found that the dye irriates other animals such as crabs,
sea urchins, fishes and bristleworms. It is believed that the dye
is a by-product of the seaweeds that the sea hare eats. Some kinds
of sea hares may have a gland that produces a white secretion. Sea
hares may also store in their skin, distasteful and even toxic chemicals
that they obtain from the seaweed that they eat.
Hare today, gone tomorrow! Sea
hares do not live long as large, mature adults, rarely longer than
a year. They die soon after they reproduce. They are hermaphrodites,
each animal having both male and female reproductive organs. The male
organ appears on the neck, and the female opening is within the body
mantle. Some sea hares are said to form mating chains, each one acting
as male to the one in front of it and as a female to the one behind.
They lay eggs in strings or ribbons. There is often a seasonal abundance
of sea hares on our shores, with not a hare in sight in between.
Human uses: It is said that some
Pacific Islanders eat sea hares. Yet again, there are reports of dogs
being poisoned after eating sea hares. It appears that the algae that
the sea hares eat may be responsible for the toxins.
Status and threats: None of our
sea hares are listed among the threatened animals of Singapore. However,
like other creatures of the intertidal zone, they are affected by
human activities such as reclamation and pollution. Trampling by careless
visitors can also have an impact on local populations.
pairs of tentacles
Changi, Jun 05
pair of flaps cover the body,
thin internal shell.
Changi, Jun 07
release a purple dye when disturbed
Pulau Sekudu, Apr 05
seen half buried in soft ground.
Changi, Apr 12
Changi, Jun 05
Cyrene Reef, Apr 10
Photo shared by Toh Chay Hoon on her
A mating pair with one nestled between the
parapodia of another!
sea hares of Singapore
sea hares of Singapore
Pulau Hantu, Aug 14
Photo shared by Marcus Ng on flickr.
Anaspidea recorded for Singapore
Tan Siong Kiat and Henrietta P. M. Woo, 2010 Preliminary Checklist
of The Molluscs of Singapore.
- 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.
- Wee Y.C.
and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore.
National Council on the Environment. 163pp.
- Chou, L.
M., 1998. A
Guide to the Coral Reef Life of Singapore. Singapore Science
Centre. 128 pages.
Helmut, 2001. Nudibranchs
and Sea Snails: Indo-Pacific Field Guide IKAN-Unterwasserachiv, Frankfurt. 321 pp.
- Wells, Fred
E. and Clayton W. Bryce. 2000. Slugs
of Western Australia: A guide to the species from the Indian to
West Pacific Oceans.
Western Australian Museum. 184 pp.
Neville. 2001. 1001
Nudibranchs: Catalogue of Indo-Pacific Sea Slugs. Neville
Coleman's Underwater Geographic Pty Ltd, Australia.144pp.
Neville, 1989. Nudibranchs
of the South Pacific Vol 1. 64 pp.
- Humann, Paul
and Ned Deloach. 2010. Reef
Creature Identification: Tropical Pacific New World Publications.
- Kuiter, Rudie
H and Helmut Debelius. 2009. World
Atlas of Marine Fauna. IKAN-Unterwasserachiv. 723pp.