Gnathophausia childressi, New Species, a Mysid from Deep Near-Bottom Waters off California, with Remarks on the Mouthparts of the Genus Gnathophausia

Gnathophausia childressi, new species (Mysidacea: Lophogastrida), discovered by Dr. J. J. Childress in 1985, is described. It was caught in the benthic boundary layer (BBL), in the deepest parts of the San Clemente Basin (at about 2,000 m), and has also been observed in the adjacent East Cortes Basin (about 1,800 m), where it has never been found in pelagic trawls fishing to depths of 1,500 m. It is closely allied to the rarest species of the genus, G. affinis, known only from the Atlantic at depths of 2,100-2,700 m, being in a manner its Pacific twin. Gnathophausia affinis apparently has the same benthopelagic habitat, which perhaps explains why it is rarely sampled. A noticeable reduction of the mandibles of G. childressi is an adaptation to this habitat. The paragnaths of all species of Gnathophausia are asymmetrical, lying closely against the posterior face of the mandibles. The left paragnath has molariform processes and it has been said that it is involved in mastication in cooperation with the movements of the left mandible. In fact, the two paragnaths are more probably involved in this function by their own musculature, perhaps a reminiscence of an ancestral function. They are not generally considered as appendages, but this is now questionable.