Hatehetfishes
Tribe Stemoptychini
by R.e. Baird
8ylvisse
Small «12 cm) silvery coloured fishes with rigid, deep,
strongly compressed body. Bony scale-like plates form keel
below ventral photophores (light organs). Pelvic fin support
bones (basipterygia) joined vertically, fins lying in vertical
plane. Dorsal pterygiophores (not dorsal fin spines) extend
beyond body margin forming blade or spine-like projection
anterior to dorsal fin rays. Prominent spines on preopercle
(posterior to jaw) and on lower body margin. Light organs
in distinct paired groups, characteristically 10-12 photophores in the major abdominal group, 6 in lower jaw or
branchiostegal group and 4 in tailor subcaudal group.
Deep-sea pelagic fishes; juveniles and larvae generally
found deeper than 150 m; adults mesopelagic, usually
below 200 m, rarely in surface waters. Common in all
oceans including Mediterranean Sea; nowhere abundant or
commercially important. Three genera with about 31
species; 12 species of hatchetfishes proper can be expected
to occur in our area.
KEY TO GENERA
la Abdominal photophores 12; eyes telescopic,
dorsally oriented; several pterygiophores form
extensive blade anterior to D .............. .. .............. Argyropelecus
Ib Abdominal photophores 10; eyes normal; dorsal
blade consisting of only 1 or 2 spines from a
single or 2 fused pterygiophores ............................. ....... ....... 2
2a Anal photophores 6 or greater; a lateral
photophore; dorsal blade reduced; no large
transparent membrane above A rays .......................... Polyipnus
A S
SR
Argyropelecu$
75: STERNOPTYCHIDAE (HATCHETFISHES)
2b Anal photophores 3; no lateral photophore;
single large D spine with anterior serrate margin;
A support elements greatly enlarged, with triangulate
transparent membrane above fin rays ........................ Sternoptyx
Genus Argyropelecus Cocco, 1829
Seven species; 4 in our area and 1 probably occurs rarely.
KEY TO SPECIES
la Supra-abdominal, preanal, anal and subcaudal
photophores in a nearly continuous straight line;
distinct gap between each subcaudal photophore ............ .... .. .... 3
Ib Supra-abdominal, preanal, anal and subcaudal photophores
not in a continuous straight line; subcaudal photophores in
a continuous group set off from last anal photophore ...... ........... 2
2a A single, posteriorly directed, serrate , postabdominal
spine; Drays 8; trunk and caudal region elongate ... A. hemigymnus
2b Two separate post abdominal spines; Drays 9 .......................... 4
3a Dorsal blade height less than l) its length; body
margin not markedly raised posterior to dorsal
blade; ventral keel scales do not extend below
abdominal photophores .. .... ............... .... .... ... ....... .. ... A . affinis
3b Dorsal blade height more than l) its length; body
margin markedly raised posterior to dorsal blade;
ventral keel scales extend well below abdominal
photophores forming flap-like process; prominent
laterally directed spine near dorsoposterior edge of
eye ................. .... ... ............ ..... .. ..... ................. .. ... . A . gigas
4a Posterior postabdominal spine directed posteroventrally
and markedly larger than the anterior spine; pair
of enlarged canine teeth in lower jaw; subcaudal
spines of about equal length and size; pair of
large canine teeth in lower jaw ........ ........ ....... .... .... A . aculeatus
4b Postabdominal spines subequal; subcaudal spines
absent; no large canine teeth .. . .. .. .... .. .. .. .... .. ... .. ........ A. sladeni
••
Sternoptyx
PolyipnU$
Diagrammatic configuration of photophores and other external features ofthethree hatchetfish genera: AB = abdominal, AN = anal, BR = branchial, DB = dorsal blade,
OS = dorsal spine, I = isthmus, L = lateral. PAN = pre-anal. PAS = post-abdominal spine, PO = preorbital. PRO = preopercular, PTO = postorbital,
PTS = post-temporal spine, SAB = supra-abdominal, SAN = supra-anal, SC = subcaudal, SO = subopercular, SP = suprapectoral, TM = transparent membrane.
Pectoral fins not shown.
255
Tribe Stemoptychini
by R.e. Baird
8ylvisse
Small «12 cm) silvery coloured fishes with rigid, deep,
strongly compressed body. Bony scale-like plates form keel
below ventral photophores (light organs). Pelvic fin support
bones (basipterygia) joined vertically, fins lying in vertical
plane. Dorsal pterygiophores (not dorsal fin spines) extend
beyond body margin forming blade or spine-like projection
anterior to dorsal fin rays. Prominent spines on preopercle
(posterior to jaw) and on lower body margin. Light organs
in distinct paired groups, characteristically 10-12 photophores in the major abdominal group, 6 in lower jaw or
branchiostegal group and 4 in tailor subcaudal group.
Deep-sea pelagic fishes; juveniles and larvae generally
found deeper than 150 m; adults mesopelagic, usually
below 200 m, rarely in surface waters. Common in all
oceans including Mediterranean Sea; nowhere abundant or
commercially important. Three genera with about 31
species; 12 species of hatchetfishes proper can be expected
to occur in our area.
KEY TO GENERA
la Abdominal photophores 12; eyes telescopic,
dorsally oriented; several pterygiophores form
extensive blade anterior to D .............. .. .............. Argyropelecus
Ib Abdominal photophores 10; eyes normal; dorsal
blade consisting of only 1 or 2 spines from a
single or 2 fused pterygiophores ............................. ....... ....... 2
2a Anal photophores 6 or greater; a lateral
photophore; dorsal blade reduced; no large
transparent membrane above A rays .......................... Polyipnus
A S
SR
Argyropelecu$
75: STERNOPTYCHIDAE (HATCHETFISHES)
2b Anal photophores 3; no lateral photophore;
single large D spine with anterior serrate margin;
A support elements greatly enlarged, with triangulate
transparent membrane above fin rays ........................ Sternoptyx
Genus Argyropelecus Cocco, 1829
Seven species; 4 in our area and 1 probably occurs rarely.
KEY TO SPECIES
la Supra-abdominal, preanal, anal and subcaudal
photophores in a nearly continuous straight line;
distinct gap between each subcaudal photophore ............ .... .. .... 3
Ib Supra-abdominal, preanal, anal and subcaudal photophores
not in a continuous straight line; subcaudal photophores in
a continuous group set off from last anal photophore ...... ........... 2
2a A single, posteriorly directed, serrate , postabdominal
spine; Drays 8; trunk and caudal region elongate ... A. hemigymnus
2b Two separate post abdominal spines; Drays 9 .......................... 4
3a Dorsal blade height less than l) its length; body
margin not markedly raised posterior to dorsal
blade; ventral keel scales do not extend below
abdominal photophores .. .... ............... .... .... ... ....... .. ... A . affinis
3b Dorsal blade height more than l) its length; body
margin markedly raised posterior to dorsal blade;
ventral keel scales extend well below abdominal
photophores forming flap-like process; prominent
laterally directed spine near dorsoposterior edge of
eye ................. .... ... ............ ..... .. ..... ................. .. ... . A . gigas
4a Posterior postabdominal spine directed posteroventrally
and markedly larger than the anterior spine; pair
of enlarged canine teeth in lower jaw; subcaudal
spines of about equal length and size; pair of
large canine teeth in lower jaw ........ ........ ....... .... .... A . aculeatus
4b Postabdominal spines subequal; subcaudal spines
absent; no large canine teeth .. . .. .. .... .. .. .. .... .. ... .. ........ A. sladeni
••
Sternoptyx
PolyipnU$
Diagrammatic configuration of photophores and other external features ofthethree hatchetfish genera: AB = abdominal, AN = anal, BR = branchial, DB = dorsal blade,
OS = dorsal spine, I = isthmus, L = lateral. PAN = pre-anal. PAS = post-abdominal spine, PO = preorbital. PRO = preopercular, PTO = postorbital,
PTS = post-temporal spine, SAB = supra-abdominal, SAN = supra-anal, SC = subcaudal, SO = subopercular, SP = suprapectoral, TM = transparent membrane.
Pectoral fins not shown.
255