learn only 3 things about them ...
Super stars of the echinoderms: they are the largest group
of echinoderms, fastest moving, most nervous--falling
Although numerous, they are shy and seldom seen.
live inside sponges and on other animals.
Brittle stars are the most common echinoderms on our shores but are
rarely seen as they shun the light and are more active at night. Often,
all that can be seen of a brittle star are its skinny, spiny arms!
Ones with longer arms may be seen hiding among coral rubble. Tiny
ones shelter under rocks, beneath the sand and in even on other animals
such as sponges.
What are brittle stars? Brittle
stars belong to Phylum Echinodermata
and Subclass Ophiuroidea which has about 2,100 known species. This
makes Ophiuroidea the largest group of echinoderms. About 300 brittle
star species are found in shallow tropical waters.
Features: Brittle stars are related
to sea stars but belong to a different class and have somewhat different
features and habits. Like other echinoderms, brittle stars are symmetrical
along five axes, have spiny skin and tube feet.
An armful: A brittle star is almost all arms. Its central
disk is usually only a few centimeters wide while its thin, flexible
arms can be very long. The arms are made up of large, well developed
ossicles (plates made mostly of calcium carbonate). The ossicles are
connected together like a vertebrate with ball-and-socket joints.
A brittle star lengthens its arms by adding ossicles where the arm
joins the central disk.
Sometimes confused with
Here's more on how to tell them
apart. Feather stars
may also appear similar but they usually have 10 or more arms.
Speedy stars: Brittle stars are the fastest-moving echinoderms!
While sea stars use their tube feet to move slowly, brittle stars
use their highly flexible, spiny arms instead. Their arms move in
a snaky manner, 'Ophiuroidea' means 'snake-like'.
To move, a brittle star generally gets a grip on something with one
or two spiny arms. These then pull while the remaining arms push or
trail behind. Some brittle stars may also 'swim' by vigorously rowing
their highly flexible arms, similar to the breast-stroke!
Falling apart: As its name suggests,
a brittle star has a tendency to fall apart. It may purposely throw
off an arm when threatened. So please don't handle brittle stars.
The dropped arm may continue to wriggle to distract the predator while
the brittle star escapes. The brittle star is able to do this because
the ossicles in its arms are connected by mutable connective tissue.
The brittle star can rapidly change the consistency of this tissue
from rock hard to almost liquid. The arm eventually re-grows, but
it can take months before it is fully restored.
Brittle stars have only one opening on their underside that functions
as both a mouth and anus! Unlike sea stars, the digestive system of
brittle stars doesn't extend into their arms. A brittle star's mouth
is surrounded by jaws made up of a circle of five large toothed plates
that meet in the middle. Unlike sea urchins, the jaws cannot be extended
What do they eat? Many brittle
stars feed on detritus, using their arms to gather this from the surface
or to filter these out of the water. Unlike sea stars, a brittle star
doesn't have a groove on the underside of its arms.
Tiny tube feet emerge from holes between the ossicles in the arms.
These may 'wipe off' food particles stuck on the hooked or mucous-coated
spines, or collect particles off the surface, and pass these on to
the central mouth. Other brittle stars are carnivores that use their
arms to sweep tiny creatures to their mouths. Yet others are scavengers,
nibbling on their food with their jaws or using the tube feet near
their mouth. Some brittle stars use their tube feet to sense chemicals
released by their food.
Stars come out at night: Brittle
stars are plentiful but seldom seen. They have many predators, so
brittle stars usually only come out at night. Creatures that snack
on brittle stars include fish, crabs, hermit crabs, mantis shrimp
and even sea stars and other brittle stars.
Star-spangled sponges: Tiny brittle
stars (1-2cm with arms) often live inside sponges.
Look closely at the holes of a sponge and you might see their little
arms sticking out. They may also be found living with corals and even
other echinoderms. One tiny brittle star Ophiosphaera insignis
lives near the mouth of the sea urchin Diadema setosum. Here,
the brittle star finds safety and food that is gathered by the sea
urchin. Another tiny brittle star Ophiomaza
cacaotica shelters near the mouth of feather
stars. Yet others cling to the branches of gorgonians.
Brittle star babies: Most brittle
stars have separate genders and are usually either male or female.
Sperm or eggs are stored in pouch-like chambers in the central disk.
These are usually released simultaneously into the water. This usually
happens at night. Some spawning brittle stars assume a push-up posture,
raising the central disk into the water currents by standing on the
tips of their arms.
Brittle stars undergo metamorphosis and their larvae look nothing
like their adults. The form that first hatches from the eggs are bilaterally
symmetrical and free-swimming, drifting with the plankton. They eventually
settle down and develop into tiny brittle stars. Some brittle stars
brood their eggs.
Basket case: Included in Class
Ophiuroidea are the basket stars (Suborder
Euryalina) that have branched arms and thus appear basket-like. Large
ones are generally found in deeper water, although small ones have
been encountered on the intertidal.
Human uses: Brittle stars are
not used for human purposes.
stars on Singapore shores
Ophiuroidea recorded for Singapore
Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in
*additions from Lane, David J.W. and Didier Vandenspiegel. 2003. A
Guide to Sea Stars and Other Echinderms 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.
stars seen awaiting identification
Brittle stars can
only be positively identified from microscopic examination of
their internal parts and are thus difficult to distinguish in
the field. On this website, unidentified brittle stars seen
are grouped by general colour and pattern for convenience of
*Ophiosphaera insignis (**previously in Family Ophiactidae)
savignyi (Tiny in-a-sponge brittle star)
*Ophiactis maculosa=**Ophiactis savignyi
*Ophiactis sinensis=**Ophiactis picteti
*Ophiactis versicolor=**Ophiactis savignyi
lineocaerulea=Ophiothrix lineocaerulea (Blue-lined brittle star)
longipeda (Very long-armed brittle star)
Ophiomaza cacaotica (Feather-hitching brittle star)
*Ophiothela danae (Tiny colourful brittle star)
(Upsidedown brittle star)
Ophiothrix galatheae=**Macrophiothrix galatheae
*Ophiothrix melanosticta=**Macrophiothrix melanosticta
Ophiothrix nereidina=**Macrophiothrix nereidina
*Ophiothrix propinqua=**Macrophiothrix propinqua
Euryale aspersa (DD:
EN? Data deficient, possibly Endangered)
- Lane, David
J.W. and Didier Vandenspiegel. 2003. A
Guide to Sea Stars and Other Echinoderms of Singapore.
Singapore Science Centre. 187pp.
- Chou, L.
M., 1998. A
Guide to the Coral Reef Life of Singapore. Singapore Science
Centre. 128 pages.
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.
- Wee Y.C.
and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore.
National Council on the Environment. 163pp.
Terrence M., David W. Behrens and Gary C. Williams. 1996. Coral
Reef Animals of the Indo-Pacific: Animal life from Africa to Hawaii
exclusive of the vertebrates
Sea Challengers. 314pp.
- Allen, Gerald
R and Roger Steene. 2002. Indo-Pacific
Coral Reef Field Guide.
Tropical Reef Research. 378pp.
- Edward E.
Ruppert, Richard S. Fox, Robert D. Barnes. 2004.Invertebrate
Brooks/Cole of Thomson Learning Inc., 7th Edition. pp. 963
Jan A., 2005. Biology
of the Invertebrates.
5th edition. McGraw-Hill Book Co., Singapore. 578 pp.
Gordon, John E. Miller, David L. Pawson and Porter M. Kier, 1995.
Stars, Sea Urchins, and Allies: Echinoderms of Florida and the
Smithsonian Institution Press. 390 pp.
Sabine, 2000. Echinoderms
of the Philippines: A guide to common shallow water sea stars,
brittle stars, sea urchins, sea cucumbers and feather stars.
Times Edition, Singapore. 144 pp.
Neville. undated. Sea
Stars of Australasia and their relatives. Neville Coleman's
World of Water, Australia. 64pp.