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Starfishes
Starfishes belong to the Phylum Echinodermata. Other groups belonging to the Echinodermata are the Brittle Stars, feather stars, sea urchins and sea cucumbers.
The pentagonal shape that is inherent in the echinoderms is apparent in the physical form of starfishes. Most species in Malaysian waters have five arms although one may find a specimen with one more arm or less. The usefulness of these arms is aplenty. As predators, starfishes feed on a great variety of bottom-dwelling creatures such as bivalves, clams, crustaceans, worms and even other echinoderms. The starfish uses its arms to entrap the prey, then throws part of its stomach out of its mouth to envelop the victim. This process enables them to digest externally. The tube feet, which are found lining the undersides of the arms, are used for mobility and on top of that, the powerful suction capabilities are sometimes used to pry open bivalves. These tube feet are connected to what is known as the 'water vascular system'. The water is pumped through the feet, which in turn responds by contracting and retracting.
This starfish is often seen during dives and is not uncommon in shallower waters suitable for snorkelling. Sometimes, comets of the starfish are found. Starfishes have amazing regenerative powers. If there are bits of starfishes left behind by predators, for example, that piece - known as comet can regenerate and build itself into a whole new starfish in as little time as a few weeks.
The beautifully designed red tipped starfish uses the water vascular system, like all other echinoderms, to retract and expand its arms for mobility. The water is drawn through the sieve plate located on the central mass area. This plate is obvious in this starfish…painted in a red patch.
A diver would have a greater chance of meeting these large starfishes during a night dive. The Giant Sea Star is easily recognised by its crimson colour and its enormous size as compared with the other species. The starfish has 5 equal segments, each having a duplicate set of internal organs. The mouth is located centrally on the underside and its anus is on its topside or aboral surface.
This starfish has very thick arms and can inflate themselves into a blobbish ball. The Pin cushion sea star has tiny symbiotic shrimps living on the lower surfaces. It feeds on coral polyps, by stifling the patch of polyps with its body and throwing its gut out of its mouth to ingest the polyps externally. Sometimes, pearl fishes are found living in its gut.
The multi -armed Crown-of-thorns have a terrible reputation for killing corals especially when there is a plague of them. Regular divers are encouraged to destroy them whenever they chance upon these infamous creatures during their dives. The Hongkong and Shanghai Bank sponsor a once a year Crown-of-thorn clean up jamboree on Pulau Redang to rid these pests from the marine parks. These dangerous starfishes have toxic substances in their prickly thorns and can inflict much pain and hence only experienced recreational(and beyond) divers are allowed to participate in this jamboree, volunteering their services.
There are however, two schools of thought. Some scientists argue that over-fishing , over harvesting of the crown-of-thorn's predator especially the triton conch, and excess pollution had exarcebated the conditions where these starfishes have plagued entire coral reefs, reducing them to a graveyard of corals. The crown-of-thorn relishes on live coral polyps. Other scientists believe that plagues are natural phenomenon and that reducing the spread of dominant coral species may encourage species diversity on the reef by allowing space for other slow growing corals to expand. Moreover, they insist that plagued coral patches have recovered relatively quickly and that continuous removal of these starfishes may have an adverse long-term effect.
Brittle stars
Brittle stars are similar in appearance to starfishes but have thin, brittle arms that are composed of individual calcareous segments held together by muscle. This enables them to move its entire arm when scuttling on the bottom. An incredibly shy animal and light sensitive, these creatures are hardly seen in the open during the day. When disturbed, they have a special ability of breaking off parts or even whole arms as decoy while it makes for shelter. Many feed on organic matter by sieving through sand and mud, and others filter plankton animals from the currents. Some brittle star species tunnel into the sandy bottoms, covering the disk shaped body and upper arms, leaving only the tips of the arms flying in the current to catch passing organic matter and detritus.
This animal is often seen clinging on to sponges and sea gorgonian fans, forming symbiotic relationships with them where they feed on organic debris that cling on to the surface of its host. Brittle Stars have only one set of internal organs (unlike the sea stars), have a mouth on the underside but no separate anal opening on the topside.
This brittle star is often found in a symbiotic relationship with black corals. It wraps its smooth arms round the coral branches and feeds off the organic matter that clings on to the surface of its host.
Feather Stars or Chrinoids
Feather stars are often seen sticking out of sea gorgonian fans or edges of sponges. They anchor themselves on their host using a set of short clasping, tubular arms known as cirri. These arms are also used to travel from one place to another on the sandy bottom or on their host. The longer feathery arms that extends especially during the night when feeding activity is at its peak, can number as many as 30 in some species. The feathery arms have short side branching which excretes a film of mucus used to trap plankton organisms floating by in the current. The trapped food is transferred to the mouth located at the central disk, by using a system of grooves in the tube feet.
Some are nocturnal while others are diurnal and some feed both day and night. The Feather Stars are extremely sensitive to strengths and direction of current flow, moving their arms for maximum area exposure when currents change directions. When the current gets too strong, they retract their arms or move to areas where they can get a stronger foothold.
This star can often be seen on sea gorgonian fans in the outer reef slopes where currents are almost continuous. They have 20 - 30 arms, which are extended into the currents to entrap passing plankton matter.
This feather star comes in a variety of colours and is usually seen in clear waters, bathed with strong currents between a depth range of 6 - 30m . They are often seen clinging on to sea gorgonian fans and whip corals. The side branches or pinnules secrete a thin film of mucus slime used to trap passing food. Look closer and one would often see a host of symbiotic creatures such as tiny shrimps, crabs and clingfishes making home or taking shelter among the arms.
Illustrations provided by Dennis Ho: Underwater photography by Moti Uttam
Corals & Fishes in Malaysia
| Corals - Hard & Soft Corals | Eels | Sharks | Rays | Octopus | Squids and Cuttlefish | Nautilus | Nudibranchs | Clams | Starfish | Brittlestars | Featherstars | Sea Urchins | Sea Cucumbers | Worms | Sponges | Jellyfish | Damselfish | Butterflyfish | Angelfish | Surgeonfish | Parrotfish | Wrasse | Triggerfish | Batfish | Trumpetfish | Squirrelfish | Catfish | Grouper | Athias | Sweetlips | Fusiliers | Puffers | Filefish | Trevally | Snappers | Scorpionfish | Cardinalfish | Goby | Barracuda | Rainbow Runner | Pompano | Bream | Goatfish |
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