Family No. 228: CHIASMODONTIDAE
by R.K. Johnson & M.J. Keene
Swallowers
Slukkers
Body moderately compressed, elongate. Dorsal fin IXXIII + 18-29. Dorsal fin spines flexible. Anal fin 1,17-29.
Pectoral fin rays 9-15. Pelvic fins 1,5. Branchiostegal rays 6
or 7 (2 on epihyal). Vertebrae 33-48. Body naked (Kali,
Chiasmodon (half-grown, adults)), scabrous, with numerous small projecting spinules (Chiasmodon, postlarvae,
juveniles), or with 2 or more rows of larger (and fewer),
stout, projecting prickles (Dysalotus). Mouth large with
long teeth. Premaxilla and maxilla slender and elongate,
firmly connected distally. Jaw teeth in 1 or 2 rows (Chiasmodon, Kali) or in bands 3-5 teeth wide tapering to 1 or 2
rows posteriorly (Dysalotus). Teeth present on palatines,
present or absent on vomer. Lath-like gill-rakers lacking,
replaced (Dysalotus, Kali, but not Chiasmodon) with short
gill teeth, fixed (1-3 teeth per plate) on nodular bony plates.
Post-temporal bone distinctly forked, with ventral limb
connected (via a ligament) to opisthotic. All chiasmodontids
with a rather uniform blackish or brownish pigmentation
over entire body and fins, without any distinct concentration
into bars, stripes or other markings. Photophores lacking.
Chiasmodontids are oceanic and mesopelagic or bathypelagic piscivorous fishes. They reach a relatively large size
for midwater fishes (record for family: 262 mm SL in Kali
indica). Their ability to swallow large prey, sometimes as
large as themselves, has earned them the name "swallowers". The anterior anal fin pterygiophores are not embedded in the musculature, enhancing the ability of the
stomach to expand and accommodate large prey. Nothing is
known of the behaviour or reproduction of chiasmodontids.
The family is circumglobal in tropical and subtropical
oceanic areas, but of no commercial importance. Three
genera with a total of 11 currently recognised species, 9
species in our area or likely to occur here. The most recent
revisions are those by Norman (1929), Johnson (1969), and
Johnson & Cohen (1974).
KEY TO GENERA
(Adults)
la Jaw teeth arranged in bands up to 3-4 teeth
wide; large prickles along sides of body ....................... Dysalotus
Ib Jaw teeth in 1 or 2 rows, large prickles lacking ......................... 2
2a None of 3 anteriormost jaw teeth are as long as
some more posterior teeth in inner row; tooth plates
(small nodules of bone with 1-3 tiny teeth per plate)
present on 1st 3 gill arches; vertebrae 33-41 ......................... Kali
2b One or more of 3 anteriormost jaw teeth distinctly
longer than any posterior tooth; no gill tooth
plates; vertebrae 43-48 ........................................ Chiasmodon
228: CHIASMODONTIDAE (SWALLOWERS)
Genus Chiasmodon Johnson, 1863
Four currently recognised species, 2 off southern Africa.
The genus needs revision; information presented here 'is
based on the literature or on examination of limited material, most of it from the Atlantic.
KEY TO SPECIES
la Teeth strong; head 27-31 % SL; snout 22-25%
head length; interorbital width 18-20% head
length ..................................................................... C. niger
Ib Teeth moderate in size; head 23-27% SL; snout
27-30% head length; interorbital width 21-23%
head length ........................................................ C. bolangeri
228.1 Chiasmodon bo/angeri
Osorio, 1909
Chiasmodon bolangeri Osorio, 1909: 22, PI. 2, Fig. 1 (offSetubal, Portugal). Chiasmodon microcephalus Norman, 1929: 539, Fig. 86 (South
Atlantic, 39°50'S, 36°23'W and 33°25'S, 06°31'E).
D XI-XIII+26-29; A 1,26-29; P 12-15; vertebrae 43-46. Teeth smaller
and weaker, but otherwise arranged exactly as in C. niger. Spine at lower
angle of preoperculum weakly developed.
Most captures below 750 m. Not yet recorded from our
area but has been taken at 33°25'S, 06°37'E. Tropical/subtropical in Atlantic Ocean.
228.1 Chiasmodon bolangeri: head of 11.5 cm holotype of C. microcephalus
(drawn after Norman, 1929).
228.2 Chiasmodon niger
Johnson, 1863
Chiasmodon niger Johnson, 1863: 408 (off Madeira); Goode & Bean,
1896: 292*; Barnard, 1927: 434; Smith, SFSA No. 377*. Chiasmodus
niger: Gunther, 1864: 45 (invalid emendation of Chiasmodon); Gilchrist
& von Bonde, 1924: 12.
D XI-XIII+26-29; A 1,26-29; P 12-15; vertebrae 43-46. Teeth more
strongly developed than in C. bolangeri, acutely pointed, in 2 series in
each jaw. Expanded part of premaxilla with 3 canine teeth, the 1st fixed
and strongly curved, the 2nd of moderate size, depressible, directed posteriorly, and lying flat against roof of mouth when not erected; the 3rd very
large, depressible, crossing that of the opposite side when laid back; 3
anterior teeth on each dentary also enlarged, the 1st fixed, the 3rd very
long (see Norman, 1929). A small but stout spine at lower angle of
preopercle.
731
by R.K. Johnson & M.J. Keene
Swallowers
Slukkers
Body moderately compressed, elongate. Dorsal fin IXXIII + 18-29. Dorsal fin spines flexible. Anal fin 1,17-29.
Pectoral fin rays 9-15. Pelvic fins 1,5. Branchiostegal rays 6
or 7 (2 on epihyal). Vertebrae 33-48. Body naked (Kali,
Chiasmodon (half-grown, adults)), scabrous, with numerous small projecting spinules (Chiasmodon, postlarvae,
juveniles), or with 2 or more rows of larger (and fewer),
stout, projecting prickles (Dysalotus). Mouth large with
long teeth. Premaxilla and maxilla slender and elongate,
firmly connected distally. Jaw teeth in 1 or 2 rows (Chiasmodon, Kali) or in bands 3-5 teeth wide tapering to 1 or 2
rows posteriorly (Dysalotus). Teeth present on palatines,
present or absent on vomer. Lath-like gill-rakers lacking,
replaced (Dysalotus, Kali, but not Chiasmodon) with short
gill teeth, fixed (1-3 teeth per plate) on nodular bony plates.
Post-temporal bone distinctly forked, with ventral limb
connected (via a ligament) to opisthotic. All chiasmodontids
with a rather uniform blackish or brownish pigmentation
over entire body and fins, without any distinct concentration
into bars, stripes or other markings. Photophores lacking.
Chiasmodontids are oceanic and mesopelagic or bathypelagic piscivorous fishes. They reach a relatively large size
for midwater fishes (record for family: 262 mm SL in Kali
indica). Their ability to swallow large prey, sometimes as
large as themselves, has earned them the name "swallowers". The anterior anal fin pterygiophores are not embedded in the musculature, enhancing the ability of the
stomach to expand and accommodate large prey. Nothing is
known of the behaviour or reproduction of chiasmodontids.
The family is circumglobal in tropical and subtropical
oceanic areas, but of no commercial importance. Three
genera with a total of 11 currently recognised species, 9
species in our area or likely to occur here. The most recent
revisions are those by Norman (1929), Johnson (1969), and
Johnson & Cohen (1974).
KEY TO GENERA
(Adults)
la Jaw teeth arranged in bands up to 3-4 teeth
wide; large prickles along sides of body ....................... Dysalotus
Ib Jaw teeth in 1 or 2 rows, large prickles lacking ......................... 2
2a None of 3 anteriormost jaw teeth are as long as
some more posterior teeth in inner row; tooth plates
(small nodules of bone with 1-3 tiny teeth per plate)
present on 1st 3 gill arches; vertebrae 33-41 ......................... Kali
2b One or more of 3 anteriormost jaw teeth distinctly
longer than any posterior tooth; no gill tooth
plates; vertebrae 43-48 ........................................ Chiasmodon
228: CHIASMODONTIDAE (SWALLOWERS)
Genus Chiasmodon Johnson, 1863
Four currently recognised species, 2 off southern Africa.
The genus needs revision; information presented here 'is
based on the literature or on examination of limited material, most of it from the Atlantic.
KEY TO SPECIES
la Teeth strong; head 27-31 % SL; snout 22-25%
head length; interorbital width 18-20% head
length ..................................................................... C. niger
Ib Teeth moderate in size; head 23-27% SL; snout
27-30% head length; interorbital width 21-23%
head length ........................................................ C. bolangeri
228.1 Chiasmodon bo/angeri
Osorio, 1909
Chiasmodon bolangeri Osorio, 1909: 22, PI. 2, Fig. 1 (offSetubal, Portugal). Chiasmodon microcephalus Norman, 1929: 539, Fig. 86 (South
Atlantic, 39°50'S, 36°23'W and 33°25'S, 06°31'E).
D XI-XIII+26-29; A 1,26-29; P 12-15; vertebrae 43-46. Teeth smaller
and weaker, but otherwise arranged exactly as in C. niger. Spine at lower
angle of preoperculum weakly developed.
Most captures below 750 m. Not yet recorded from our
area but has been taken at 33°25'S, 06°37'E. Tropical/subtropical in Atlantic Ocean.
228.1 Chiasmodon bolangeri: head of 11.5 cm holotype of C. microcephalus
(drawn after Norman, 1929).
228.2 Chiasmodon niger
Johnson, 1863
Chiasmodon niger Johnson, 1863: 408 (off Madeira); Goode & Bean,
1896: 292*; Barnard, 1927: 434; Smith, SFSA No. 377*. Chiasmodus
niger: Gunther, 1864: 45 (invalid emendation of Chiasmodon); Gilchrist
& von Bonde, 1924: 12.
D XI-XIII+26-29; A 1,26-29; P 12-15; vertebrae 43-46. Teeth more
strongly developed than in C. bolangeri, acutely pointed, in 2 series in
each jaw. Expanded part of premaxilla with 3 canine teeth, the 1st fixed
and strongly curved, the 2nd of moderate size, depressible, directed posteriorly, and lying flat against roof of mouth when not erected; the 3rd very
large, depressible, crossing that of the opposite side when laid back; 3
anterior teeth on each dentary also enlarged, the 1st fixed, the 3rd very
long (see Norman, 1929). A small but stout spine at lower angle of
preopercle.
731