Pram Bug (Phronima)

© 2000 by Image Quest 3-D
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This deep sea amphipod genus is particularly renowned for its house-building. This transparent organism feeds upon free-living, planktonic sea squirts and salps. It devours the internal soft body parts of its live prey and is then left surrounded by a tough, transparent husk of tunicin. It is this outer casing that it then modifies to form an open-ended barrel, the final shape of which is particular to the species of Phronima and the salp in question.

This macabre activity seems to be conducted by the female amphipods, and in time eggs or hatchlings are deposited as a saddle on the inner wall of the barrel (see above). Here they remain and grow, aerated by a constant flow of water that moves through the barrel as the female swims through the water column. With advancing age comes the spirit of adventure and juveniles start to stray from their brood site towards the margins of the barrel (see above).

The eyes of the adult Phronima are a further feature of wonder in an animal already beset with extraordinary habits and adaptations. It has compound eyes, like most crustacea and insects, but unlike most it has four, not two. Each pair of eyes is situated on the side of the head. The outer and inner eye of each pair are actually in contact with each other. The outer eye is surrounded by a lozenge-shaped ball of eye-facet lenses commanding an enormous field of view - perhaps 270 degrees. One pair of eyes keeps a constant watch on the world ahead, whereas the other pair views the surroundings through the transparent walls of its temporary home.

 

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2001 by Image Quest 3-D
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