Gnathophausior—PEQXJEGN AT 
401 
KEY TO THE THREE MOST COMMON GENERA 
OF THE SUBORDER LOPHOGASTRIDA 3 
1. Branchiae present on all or some of the 
thoracic limbs. Pleopods well developed in 
both sexes, natatory, unmodified. No stato- 
cyst. Marsupium with seven pairs of brood 
lamellae (oostegites) . 2 
2. Pleural plates of abdominal somites distinct 
and moderately well developed. .... 3 
2'. No pleural plates on abdominal somites. 
Outer margin of scale naked. Telson en- 
tire . Eucopia 
3. Exopod of uropod divided by a suture near 
the apex. Maxillules with endopod in the 
form of a reflexed two-segmented palp. . . 
. . . . . . . . . . . Gnathophausia 
3'. Exopod of uropod undivided; outer margin 
naked and ending in a tooth. Maxillules 
without endopod. Antennal scale heart- 
shaped, outer margin serrated . Lophogaster 
Distinguishing Characteristics 
of the Genus Gnathophausia 4 
1. CARAPACE: Rather large, only loosely cov- 
ering the trunk for most of its length, and ex- 
teriorly provided with raised longitudinal keels. 
Posterior part of carapace usually drawn out 
dorsally into a posteriorly pointing spine ( more 
pronounced in younger than in mature speci- 
mens ) . 
2. ROSTRUM: Elongated and spiniform. 
3. ANTENNULE: Antennular peduncle short 
and thick, outer flagellum greatly produced. 
4. ANTENNA: Antennal scale of somewhat 
varying form in different species. 
5. EYES: Eyes well-developed with a small 
papilla issuing from the stalk anteriorly. 
6. maxillule: Posteriorly recurved palp on 
maxillule armed with long setae especially at 
distal end. 
7. MAXILLA: Third segment has a long, 
well-chitinized lobe which is incised right to its 
3 From Tattersall and Tattersall, 1951. 
4 Compiled from Sars, 1885; Fage, 1941; and Tat- 
tersall and Tattersall, 1951. 
Fig. 2. Comparison of Isaacs-Kidd Mid water Trawl 
with non-depressing net. (From SIO Oceanographic 
Equipment Report, 1953.) 
base forming two long, slender, finger-like 
processes armed with setae only at their tips. 
On the outer side of the coxa there is a brightly 
pigmented papilla which bears the opening of 
a gland producing a luminous secretion. 
8. THORACIC LIMBS: Maxillipeds with ex- 
opodites either very small or entirely lacking. 
Remaining thoracic limbs nearly uniform, all 
provided with exopods. 
9. branchiae: Those on second to seventh 
thoracic limbs divided into four branches with 
irregularly lobed pinnules. Branchiae on eighth 
thoracic limb rudimentary. 
10. thoracic STERNITES: In males each 
thoracic sternite bears a tubercle. 
11. ABDOMEN: Abdominal segments narrow 
with small bilobed epimera. A transverse groove 
dividing the sixth abdominal segment. 
12. UROPODS: External branch broader than 
internal branch with two segments on external 
branch. 
13. TELSON: Large, constricted near the 
base; two long keels present on dorsal surface; 
lateral margins armed with spines arranged in 
series of larger spines with smaller ones be- 
tween; apex armed with two strong, curved 
spines connected at the base to form a back- 
wardly directed crescent. 
14. MARSUPIUM: Seven pairs of oostegites. 
