More shrimpy mischief and this time its another one of those ubiquitous Palaemonid shrimps that flock in tidal pools and scatter like flies before a trampling bootie. This fellow decided to ditch the dirt and go all frilly by getting on top a busily feeding crinoid (probably Comaster gracilis) on the fringing reef of Pulau Hantu. Also known as feather stars, crinoids are echinoderms like starfish, sea urchins and sea cucumbers. Known from fossils dating back to 500 million years, when the class formed a dominant part of marine fauna, crinoids are now past their heyday, with just about 550 species known worldwide.
Like sea stars and bristlestars, crinoids have a central disc with a mouth and anus on the upper side and between 10 and 200 radiating arms with feathery appendages called pinnules. Species that live in deep and dark waters have long stalks that are attached to the seafloor and are commonly called sea lilies. Shallow water species lose the stalk as they grow and are able to wander about in search of ideal feeding spots where the current brings in ample streams of plankton. The mesh of pinnules trap edible particles which are brought to the central disc for consumption. The little shrimp is a latecomer to the game, as many crustaceans and worms have already evolved to become associates of crinoids, making a living by pilfering food before it reaches the oral cavity.
Even more than corals, crinoids and their distant relatives the basket stars have fared poorly in Singapore's turbid waters, where the high levels of suspended sediments due to dredging for reclamation and near-shore activities probably reduce their ability to feed. The authors of this book note that many species once known from local shores are no longer present, even during intensive sub-tidal surveys in the 1990s. Lost with these frittered feathers are their associated shrimp, crabs, squat lobsters and Myzostome worms. But surprises can still emerge, as seen in the unexpected basket star spotted at Big Sister's Island recently, which could be the first record of the animal since 1896. And havens such as Pulau Hantu and Raffles Lighthouse (which thankfully is beyond the reach of most, even friendly ducks) remain to show the wealth of marine life that could exist in this sea by the city, if effort is made to mitigate the effects of anthropomorphic activities so that these waters might serve the vessels that cruise its crests as well as those who could harvest from it both food and fun.
Further reading:
Charles Messing's Crinoid Pages
Crinoidea at the Tree of Life project
Lim, G.S.Y. and L.M. Chou, The echinoderm fauna of sediment stressed reefs in Singapore. Abstract on ReefBase.org
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