Frequent visitors to rubbly shores and seagrass patches will be familiar with the incessant clicking of snapping shrimps from burrows that litter the substrate. On occasion, the shrimp can be seen out in the open as they wander about to forage or fend off faint feelings of lonesomeness with a fellow Alpheid. But usually, the crustaceans are shy beasts who greet approaching shadows by scurrying hurriedly into their labyrinth, which often lies beneath a secure chunk of rock or coral rubble. At times, the shrimp can be observed performing rigorous house-keeping duties at the entrance of its burrow. Sand and debris are shuffled out in regular clouds that the shrimp scatters to maintain a clear passage. Typically, an expanding 'fan' of fine sand radiates from the burrow, which is kept clear of algae, seagrass and other sessile growth.
The visibility of shrimp burrows and their relative density makes them ready hidey-holes for other marine creatures, from small crabs to the congregations of gobies that trap themselves in shrinking tidal pools. Often, a fleeing animal would rush into a hole only to emerge with equal haste, presumably at the furious behest of the resident shrimp. At some point lost to history, a goby or two must have deemed it wise to hang around, and over time, acquired enough goodwill to become a trusted companion for the nearly-blind shrimp, which learnt that a pair of sharp eyes can come in handy to pre-empt lunging jaws. The partners enjoy a touchy relationship whereby one of the shrimp's antennae is almost always in contact with the fish, even when they venture out to feed together. A flick of the tail compels a rapid retreat by the duo into the burrow where unspeakable acts of interspecific intercourse takes place.
This pair has been tentatively identified as Alpheus macellarius and Cryptocentrus maudae. Alpheid taxonomy is an art best left to the experts, but A. macellarius is distinguished from others in the Brevirostris Group by its distinct, traverse groove or 'saddle' on the palm of the major claw, and the specific epithet comes from the source of the holotype, a meat market on Cebu island in the Philippines. My sickly duck spotted this couple one naked evening at Sentosa's last natural shore, a stone's throw away from the rockwall that protects weekend warriors from the rich waters beyond. The goby and shrimp have also been sighted at Labrador Park's shores, which lie almost directly opposite Tanjung Rimau. But given Labrador's present state of disrepair, it's likely that few, if any, of such associations remain by the mainland for waders to mull and marvel at their mysteries that now lie buried under the muck of unmindful men.
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