10. ELECTRIC ORGANS
383
h. Snout long, tubular, and down curving. Sternarchorhynchus oryrhynchusf
hh. Snout long, tubular, horizontal and straight
i. Mouth large, opens a t least one-third the distance back to the level of the
ii. Mouth small, opens less than one-sixth the distance back to the level of the
eye; upper profile of head markedly convex. Sternarchorhamphus
eye, upper profile quite straight. Orthosternarchus tamandua“
hhh. Snout not long unless mouth is very large
j. Teeth present in both jaws; some located externally on what appear to be
swollen lips. Oedemognathus exodon
k. Dorsal region of body virtually entirely scaled from head posteriorly to
1. Mouth large, its angle extending a t least as far posteriorly as the
11. Mouth small, its angle extending no farther posteriorly than thepostekk. Scales absent from much of the body above the lateral line anterior to
the dorsal filament (shaded in Fig. 16); scales near lateral line much
larger than more dorsally. Porotergus
jj. Teeth present in both jaws but inside mouth
origin of dorsal filament
anterior margin of the eye. Sternarchus
rior naris. Sternarchella
jjj. Teeth absent from upper jaw
m. Lower jaw toothless and with a distinct midline groove into which the
beaklike upper jaw fits; middorsal region of body scaled anteriorly.
Adontosternarchus
mm. Lower jaw sometimes toothed and fitting into a midline groove in the
upper jaw; middorsal region of body naked anteriorly. Sternarchogiton
a Modified from Ellis (1913), Eigenmann and Allen (1942), and Gery and Vu-TbnTu& (1964) who should be consulted for more extensive descriptions.
Sternopygus, Eigcnmannia, Hypopornus, and Steatogenys are normally grouped together as the family Sternopygidae. Properties of the electrocytes and their innervation
indicates that Hypopomus and Steatogenys are more closely affiliated to the Rhamphichthyidae. Greenwood et al. (1966) observe “Peculiar specializations in [the gymnotids]
are many, and a complete study may alter the family arrangement accepted here.”
The author has not seen members of these genera nor are there any physiological
data from them.
Only one species is described in the taxonomic literature, but there is a second species
described here that has somewhat different rostra1 electric organ.
There is a proposed revision of Sternarchidae and Sternarchus to Apteronotidae and
Aptcronotus on grounds of priority (1800 vs. 1801). As Sternarchus has been used for a
long time and provides the basis of many other generic names in the family, the author
stands with Ellis (1913) who uses this name and derivatives.
f Although this genus has been considered to be monospecific, two apparent species
of each were found on the Rio Negro expedition of the Alpha Helix.
Martins-Ferreira, 1953; Altamirano et al., 1953). The eel emits two
classes of pulses, small pulses about 10 V in amplitude and large pulses
some 500 V or more in amplitude. All the pulses are monophasic, head
positive, and about 2 msec in duration. The voltage increases with the
length of the fish, which can exceed 1.5 meters, but even a baby 7-10
cm long can emit close to 1OOV. When the animal is resting, the small
383
h. Snout long, tubular, and down curving. Sternarchorhynchus oryrhynchusf
hh. Snout long, tubular, horizontal and straight
i. Mouth large, opens a t least one-third the distance back to the level of the
ii. Mouth small, opens less than one-sixth the distance back to the level of the
eye; upper profile of head markedly convex. Sternarchorhamphus
eye, upper profile quite straight. Orthosternarchus tamandua“
hhh. Snout not long unless mouth is very large
j. Teeth present in both jaws; some located externally on what appear to be
swollen lips. Oedemognathus exodon
k. Dorsal region of body virtually entirely scaled from head posteriorly to
1. Mouth large, its angle extending a t least as far posteriorly as the
11. Mouth small, its angle extending no farther posteriorly than thepostekk. Scales absent from much of the body above the lateral line anterior to
the dorsal filament (shaded in Fig. 16); scales near lateral line much
larger than more dorsally. Porotergus
jj. Teeth present in both jaws but inside mouth
origin of dorsal filament
anterior margin of the eye. Sternarchus
rior naris. Sternarchella
jjj. Teeth absent from upper jaw
m. Lower jaw toothless and with a distinct midline groove into which the
beaklike upper jaw fits; middorsal region of body scaled anteriorly.
Adontosternarchus
mm. Lower jaw sometimes toothed and fitting into a midline groove in the
upper jaw; middorsal region of body naked anteriorly. Sternarchogiton
a Modified from Ellis (1913), Eigenmann and Allen (1942), and Gery and Vu-TbnTu& (1964) who should be consulted for more extensive descriptions.
Sternopygus, Eigcnmannia, Hypopornus, and Steatogenys are normally grouped together as the family Sternopygidae. Properties of the electrocytes and their innervation
indicates that Hypopomus and Steatogenys are more closely affiliated to the Rhamphichthyidae. Greenwood et al. (1966) observe “Peculiar specializations in [the gymnotids]
are many, and a complete study may alter the family arrangement accepted here.”
The author has not seen members of these genera nor are there any physiological
data from them.
Only one species is described in the taxonomic literature, but there is a second species
described here that has somewhat different rostra1 electric organ.
There is a proposed revision of Sternarchidae and Sternarchus to Apteronotidae and
Aptcronotus on grounds of priority (1800 vs. 1801). As Sternarchus has been used for a
long time and provides the basis of many other generic names in the family, the author
stands with Ellis (1913) who uses this name and derivatives.
f Although this genus has been considered to be monospecific, two apparent species
of each were found on the Rio Negro expedition of the Alpha Helix.
Martins-Ferreira, 1953; Altamirano et al., 1953). The eel emits two
classes of pulses, small pulses about 10 V in amplitude and large pulses
some 500 V or more in amplitude. All the pulses are monophasic, head
positive, and about 2 msec in duration. The voltage increases with the
length of the fish, which can exceed 1.5 meters, but even a baby 7-10
cm long can emit close to 1OOV. When the animal is resting, the small