The luxury of a long, late night, in shadows that cloaked all deeds, fair or flagrant, gave us free rein of Pulau Sekudu this Friday, on a day of dry winds and air so dense it felt like a miasma of heat, a swathe of thickness and tightness that threatened to stifle thought, stir fright and turn brains into a sour slop, wanderings in a purgatory of uric pores, a stumble-through with no markers, no milestones, no intervals and no time to lose before the sun and tide return and release us from this survey of an amphibian island. The frog and other rocks that make up this islet shelter at their feet companies of crown stars, climber crabs, spiral melongenas, volcano barnacles, sea squirts, limpets and drills. Gentle slopes surround these formations and swell as dawn falls to reveal a landscape of untidy bays, of arms of sediment draped in weed and rubble, of buried rays and scooting stars. Carpets of Halophila and tangles of Ulva, which peter out into a flat of bare bottoms at the edge of the straits, teem with minute decapods, loose worms, dapper urchins, swimming anemones, naked snails and tiny Astropecten, many in a state of dishabille with arms, tubes and orifices aflutter. Under every stone is an orange portunid or a stone crab, or two, with sneering green eyes. In every hole, a claw snaps, an arm waves, a lidless eye. In every pool, countless nameless things swim, sit, stalk, slide and scatter before a light beam and a heavy boot.
Night shrimps are small carideans in the family Processidae that live in shallow flats of sand or grass, emerging after sundown to feed on lesser invertebrates, flee from other nocturnal hunters and engage in trysts between partners in red, one of whom dons a soft breeding dress and issues notes of chemical excitement to turn a touch into a feeler-up and an affair that is barely skin-deep and ends with a cuticular pocket of spermatophores. Processids remain a little-known group, understudied by carcinologists and overlooked by gourmands, save two sister species found in the Mediterranean and eastern Atlantic; in local waters, they occur in the seagrass meadows of Sekudu, Changi and Semakau as well as the coral rubble of Sentosa and the Sisters, but never seem as abundant as the palaemonids that prance about in tidal concavities, the alpheids that snuggle in dens of silt or the broken-back shrimps that lurk on bright green blades and in the dimmer reaches of broken reefs.
Large eyes with well-developed corneas and a short rostrum with an apical tooth are shared features of night shrimps, but the distinguishing feature of the family, save Ambidexter, an aberrant genus, are their dissimilar first pereopods: this pair of appendages, both of which are usually modified into powerful or dextrous chelae in most caridean families, consists in processids of a typical claw at the end of one arm and a strong dactylus or unclawed toe at the other. The second, often unequal, pereopods, meanwhile, are elongate and bear highly divided segments. The functional morphology of processids is a largely blank page: the crustaceans, clad in pigments that recall deep-sea cousins, are known to shun light and have fossorial habits. But little has been said, if at all, about how they hide. Bauer (2004) suggests that seagrass species "may well utilize preformed burrows".
Penaeids, which abound in the same habitat at Sekudu, bury themselves by using their barrage of pereiopods to displace and sink into soft sediments until nothing but their eyes are exposed. Processids, whose last three pairs of pereiopods are spindly hallmarks of the caridoid facies, employ a quite different method of digging in. Two individuals, found separately in isolated puddles, adopted a curious head-down stance after attempts to weave out of sight hit weedy barriers; each animal, though heavily berried, then plunged its forequarters into the sand before the entire shrimp vanished beneath the grains, to levels deep enough to evade probing fingers. Whether or how the first pereiopods work, perhaps in concert with rather well-developed third maxillipeds, to achieve this feat is unclear, but the creatures' ability to evade capture and elude observers by entering a lower stratum should now mark a far from final frontier for students of little beasts that spend the day in holes of their making before popping up to paddle through a bed of darkness amid a sea of stars.