SYSTEMATIC REPORT 3I 



Eight species have up to the present been referred to this genus, Gnathophausia ingens (Dohrn), 

 gigas W.-Suhm, zoea W.-Suhm, gracilis W.-Suhm, elegans G. O. Sars, longispina G. O. Sars, 

 affinis G.O. Sars and scapularis Ortmann. These species fall very sharply into two groups according 

 to the form of the antennal scale. In ingens and gigas the scale is lanceolate and unsegmented 

 with an acutely pointed apex and with the outer margin armed with teeth. In the other six species the 

 scale resembles that found in the Caridea. The outer margin is thickened to form a strong rib which 

 is produced distally into a spine from the base of which an oblique suture runs across the scale. The 

 outer margin bears a number of teeth and in one species the spine of the outer margin is dentate on 

 both its margins. 



A second character which separates ingens and gigas from the other species of the genus is the 

 peculiar modification of the epimeral plates of the last abdominal somite. In the young, these are 

 separate and distinct as in other species of Gnathophausia, but in ingens and gigas, as growth proceeds, 

 they bend under the body to fuse eventually in the median line into a single epimeral plate. 



The differences between the species are so marked that they might be considered as of generic 

 significance, ingens and gigas being placed in a separate genus, were it not for the fact that another 

 very profound difference occurs among the species which would divide the genus in quite another 

 way. In ingens, gigas and gracilis the exopod of the first thoracic appendage is present in the form 

 of a small, slender, unsegmented plate, adorned distally with a few very long plumose setae. In 

 the remaining known species of the genus the exopod of this appendage is completely lacking, but its 

 position is marked on the sympod by a shallow oval depression. If any subdivision of the genus 

 were to be made, it would be logical to arrange the species into three distinct subgenera, separating 

 ingens and gigas into a subgenus based on the form of the antennal scale, the ventral epimeral 

 plate of the last abdominal somite and the presence of an exopod on the first thoracic appendage ; 

 placing zoea, longispinis, elegans and scapularis in a second based on the form of the antennal 

 scale, the separate epimera of the sixth abdominal somite and the absence of an exopod on the first 

 thoracic appendage ; and gracilis in a third subgenus by itself, resembling the first in the form of the 

 scale and epimera of the last abdominal somite and the second in having an exopod on the first 

 thoracic appendage. 



While so few species are included in the genus there is not much point in changing the present 

 nomenclature, but if further exploration of the deep waters of the oceans should reveal many new 

 forms there would be ample grounds for the division of the genus into subgenera. 



The genus Gnathophausia includes the largest mysids which have ever been recorded. All the 

 known species are bathypelagic and no specimen has ever been taken at the surface or in very 

 shallow water. 



Only four of the known species have been collected by the ' Discovery ' : G. ingens (Dohrn), G. gigas 

 W.-Suhm, G. zoea W.-Suhm and G. gracilis W.-Suhm. 



Gnathophausia ingens (Dohrn), 1870 



1870 Lophogaster ingens Dohrn, p. 610, figs. 



1873 Gnathophausia inflata W.-Suhm, in MS. 



1885 a Gnathophausia ingens, G. O. Sars, p. 30, figs. 



1885 a Gnathophausia calcarata G. O. Sars, p. 35, figs. 



18916 Gnathophausia bengalensis Wood-Mason, J., and Alcock, A., p. 269. 



19066 Gnathophausia doryphora Illig, p. 227; 1930, p. 407, figs, (as G. ingens). 



1906 Gnathophausia ingens, Ortmann, p. 28. 



1912 Gnathophausia ingens, Hansen, p. 184; 1927, p. 15, figs. 



195 J Gnathophausia ingens, W. M. Tattersall, p. 25. 



