FISHES OF THE GULF OF MAINE 



LUMINESCENT FISHES 



141 



FAMILIES MYCTOPHIDAE, MAUROLICIDAE, CHAULIODONTIDAE, GONOSTOMIDAE, 



STOMIATIDAE, AND STERNOPTYCHIDAE 



These families include a heterogeneous assem- 

 blage of small oceanic fishes, that are primitive in 

 some respects, but are highly specialized in others 

 for existence in mid-depths, on the high seas. 



They all have light-producing organs, which no 

 other Gulf of Maine fish has; this is the only reason 

 why we group them together here. 



KEY TO GULF OF MAINE LUMINESCENT FISHES 



1. Trunk at least Yi as deep as it is long from tip of snout to base of tail fin; front part of rayed dorsal fin is a 



hard triangular plate, supported by 7 or 8 spines Hatchet fish, p. 149 



Trunk less than % as deep as it is long from tip of snout to base of tail fin; rayed dorsal fin does not commence with a 

 hard plate or hard spines 2 



2. Mouth does not gape back as far as the eye Pearl sides, p. 144 



Mouth gapes back beyond the eye 3 



3. No barbel on the chin; the ventral fins are about mid- way of the trunk; origin of rayed dorsal fin either in front of mid- 



length of trunk or at least not much behind it 4 



There is a long fleshy barbel on the chin; the ventral fins are considerably behind the mid-length of the trunk; the 

 rayed dorsal fin is far back, close to the tail fin 7 



4. The rayed dorsal fin is far in advance of the ventrals; the jaws are armed with long and conspicuous 



fangs Viperfish, p. 145 



The rayed dorsal fin is about over the ventral fins (it may be a little in front of them or a little behind) ; the teeth are 

 small 5 



5. Eyes very small; no adipose fin behind the rayed dorsal fin; anal fin reaches nearly to the base of the 



caudal Cyclothone, p. 146 



Eyes very large; there is an adipose fin behind the rayed dorsal; there is a considerable interspace between the rear end 

 of the anal fin and the origin of the tail fin 6 



6. There are 3 or 4 separate luminescent dots at the base of the caudal fin; the Gulf of Maine species has a large lumines- 



cent patch on the snout Headlight fish, p. 142 



There are only 2 separate luminous dots at the base of the caudal fin; the snout does not have a large luminescent 

 patch Lanternfish, p. 143 



7. The point of origin of the anal fin is in advance of the origin of the rayed dorsal fin by a distance about as long as 



the diameter of the eye; the tip of the chin barbel is distinctly swollen as well as bearing several 



filaments Stomioides, p. 147 



The point of origin of the anal fin is not in advance of the rayed dorsal fin, the tip of the chin barbel is not swollen.. 8 



8. Each side has only about 68 luminescent spots; there is a large luminescent patch crossing the top of the cheek, behind 



the eye; the point of origin of rayed dorsal fin is in advance of origin of anal fin by a distance about as long as the 

 diameter of the eye; the tip of the lower jaw does not enclose the tip of the upper jaw when the mouth 



is closed Trigonolampa, p. 148 



Each side has about 85 luminescent spots; the side of the cheek behind the eye does not have a large luminescent 

 patch; the point of origin of rayed dorsal fin is about over origin of anal fin; the tip of the lower jaw encloses the tip 

 of the upper jaw when the mouth is closed Stomias, p. 147 



LANTERN FISHES. FAMILY MYCTOPHIDAE 



The most distinctive external characters of the 

 lanternfishes are their large eyes (situated close to 

 the tip of the blunt snout), wide mouths gaping 

 back beyond the eye, one soft-rayed dorsal fin, a 

 deeply forked tail, and the presence of a series of 

 luminous organs as conspicuous pale spots along 

 the sides. Some of them have an adipose fin on 

 the back behind the dorsal fin, but others lack 

 this. When present, this fin is so small and 

 fragile that it is apt to be destroyed by the rough 



treatment the fish receive in the tow net in which 

 they are taken. They most aearly resemble the 

 anchovy (p. 118), the pearlsides (p. 144), and the 

 cyclothone (p. 146) among Gulf of Maine fishes; 

 but they are readily distinguished from the first 

 of these by the presence of luminous organs and 

 by the fact that the snout does not project 

 beyond the mouth; from the second by their 

 much wider mouths; and from the third by their 

 much larger eyes. 



