The amphipod genus Acidostoma

The genus Acidostoma was established by Lilljeborg (1865, p. 24) to receive Anonyx obesus Sp. Bate (1862, p. 74). Afterwards two further species have been added, viz. A. laticorne G. O. Sars (1879, p. 440) and A. nodiferum Stephensen (1923, p. 40). In the present paper it will be shown that A. laticorne as generally understood comprises two superficially similar but clearly distinct species with a widely different geographical range. On the whole the species of Acidostoma appear to be nowhere numerous and practically nothing is known about their ecology. The present writer has had access to a comparatively large number of specimens collected by the Danish Fisheries Research vessels in the North Sea. From these it was possible to draw some further information both on taxonomy and ecology. DEFINITION OF THE GENUS In most respects the Acidostoma species are typical representatives of the family Lysianassidae, but the mouth-parts are peculiar and show a series of interesting adaptations. The generic name was chosen by Lilljeborg in order to call attention to the fact that they form a long and protruding cone. The generic definition given by Lilljeborg (1865) runs as follows: "Forma corporis et antennarum cum genere Anonycis congruit, oris partes appendiculares tamen plane diversae. Labii rami laterales angusti. Mandibulae processu accessorio, maxillae 1: mi paris palpo, et palpus maxillipedum ungue carentes, et hae partes oris conjunctim acumen productum praebent. Pedes trunci 1: mi paris robusti, manu prehensili. Pedes 2: di paris graciles, ungue carentes." This definition was amplified by Della Valle (1893, p. 782), G. O. Sars (1895, pp. 37-38), and Stebbing (1906, p. 14). It was demonstrated that