These families include a heterogeneous assemblage 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 ½ 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 ¼ 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 midlength 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 luminescent 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 | |