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peculiar form of the dorsal fin certain fresh- and brackish-water fishes from




BOHNKAX KKATHKU-li.U'K ( ; \ ll.lt. Size).

West Africa and the Oriental region, one of which (Nut<>i>i<'i'n* borneensis)
is shown in the illustration herewith^ have received the not inappropriate name
of feather-backs. They constitute a family differing from all the others in
this section by the tail being tapering and fringed inferiorly by a continuation
of the anal fin, as well as by the presence of a cavity in the ring-like pterotic
bone, the base of the skull being double. Both the body and the head are
covered with small scales; barbels are wanting; the margin of the upper jaw is
formed in front by the premaxillae and at the sides by the maxilla' : and the
opercular bones are incomplete. There is no fatty fin, and the dorsal, when
present, is very short, and situated in the caudal region ; the pelvic pair being
rudimental or wanting. The air-bladder is divided internally into several com-
partments, and terminates at each end in a pair of narrow prolongations, of which
the anterior ones are in communication with the organ of hearing. A further
peculiarity is that the spawn falls into the cavity of the abdomen previous to its
exclusion. There are two Indian representatives of the genus, one of which grows
to a couple of feet in length; a third is Bomean, and the other two an' Wi
African. An extinct species has been described from the Eocene of Sumatra.

THE SOUTHERN PIKELETS, Family GALAXIIJ>.I:.

For want of a better name we may designate by the name of southern piki
lets agenusof small fresh-water lishes from ihe Southern Hemisphere, one of whicl
(Galaxias attenuating is represented in the lower figure of the illustration 01
p. 475. Together with the members of the next family, these fishes are dis-
tinguished from the other genera, of the present sectional group noticed here by
having the base of the cranium simple, the tail being rounded or forked, and the



ARAPAIMAS.



477



Z-e-





pterotic bone devoid of a cavity in its interior. Externally these fishes may be
recognised by the naked body and the absence of barbels; the fatty fin being
absent, and the medium-sized dorsal opposite the anal. Internally the air-bladder
is large and simple ; and the eggs, as in the last family, fall into the abdominal
cavity. Represented by rather more than a dozen species, the largest of which
seldom exceeds 8 inches in length, these fish are of especial interest from a
distributional point of view, since they occur in such isolated areas as New
Zealand, New South Wales, Tasmania, and the southern extremity of South
merica. From their spotted bodies, the New Zealand representatives of the genus
ere formerly known as trout by the colonists. An allied New Zealand genus
'eochanna), represented by a single species, differs in the absence of pelvic fins;
all the known specimens of this singular form having been found buried in burrows
if clay or hard mud at a considerable distance from the water.




THE ARAPAIMAS, Family OSTEOQLOSSID&

Agreeing with the last family in the conformation of the base of the skull,
the large tropical fresh-water fishes, which may be collectively known as arapaimas
(although this name properly belongs only to the Brazilian species here figured),



478 TUBE-BLADDERED GROUP.

are fully as interesting as the latter from their geographical distribution,
which presents a curious general similarity to that of the existing lung-fishes,
although in the present instance one of the genera has a much wider range than
either of the lung-fishes. In confirmation of the northern origin of the present
group, it is noteworthy that an arapaima exists in Sumatra, and also that an extinct
genus (Dapedoglossus) occurs in the Eocene strata of the United States. From the
preceding the more typical representatives of this family are structurally dis-
tinguished by the upper pharyngeal bones being three, instead of only two in number.
External!}' these fishes have the body covered with large, hard scales of a mosaic-like
structure ; the lateral line being formed by wide openings of the mucus-canal ; and
the scaleless head nearly covered with roughened ossifications of the skin. The
margin of the upper jaw is formed both by the premaxillse and maxillae, the gill-
openings are wide, and false gills are wanting. The long dorsal closely resembles
the anal fin, over which it is placed in the caudal region of the body ; both coming
very close to the tail-fin, with which they may unite as an abnormality. In
structure the air-bladder may be either simple or divided into cells.

The true arapaima (Arapaima giyas) of the larger rivers of
Brazil and the Guianas, which is the sole representative of its genus,
occupies the proud position of being the largest fresh-water bony fish, its length
not unfrequently exceeding 15 feet, while its weight may reach upwards of 400 Ibs.
As a genus, it is distinguished by the broad cleft of the mouth, in which the lower
jaw is very prominent, and the absence of barbels, as well as by the rounded lower
surface of the body, and the moderate length of the pectoral fins. In addition to
an outer series of small conical teeth in the margins of the jaws, there are rows of
rasp-like teeth not only on all the bones of the palate, but likewise on the tongue
and hyoid bones. In spite of its enormous dimensions, the arapaima is captured
by the natives of Brazil with a hook and line ; its flesh being highly esteemed as
food, and in a salted condition largely exported. It is also taken by being struck
with an arrow, to which a line is attached ; and a graphic account of this method
of hunting is given by Schomburgk. It appears that a party go out in a boat,
and row about until a fish is sighted, when the bow and arrow are brought
into requisition, and if the shot be successful, the monster is at length landed.
Barbeiied The four representatives of the typical genus Osteoylossum m:\y

Arapaimas. h e distinguished from the last by the presence of a pair of barbels to
the lower jaw, the obliquity of the cleft of the mouth, the sharp lower surface of
the body, and the greater length of the pectoral fins. Of the four species the first
is American, and has the same distribution as the true arapaima, the second occurs
in Sumatra and Borneo, while the other two are Australian. The two latter have,
however, but a very local distribution, the one (0. leicJtitrdti) being confined to the
rivers of Queensland, where it is known to the natives as the barramundi, and to
the colonists as the Dawson River salmon ; while the second (0. jardinei), which
is distinguished by the absence of a spine to the anal fin, inhabits the rivers dis-
charging into the Gulf of Carpentaria. The flesh of both these species is highly
esteemed as an article of food.

small-Mouthed The third genus of the family, which includes only a single
Arapaima. species (Hctcrotis nilotifii}, differs from both the foregoing in having



MOON-EYE AND CHISEL-JAW.



479



the pharyngeal bones numerically the same as in the southern pikelets, on which
account Professor Cope regards it as the type of a distinct family. Differing from
the other two genera in the comparatively small size of the cleft of the mouth, and
also in the approximate equality of the length of the jaws, this fish has no barbels,
and only a single series of teeth in the jaws, teeth being also present on the
pterygoid and hyoid bones, but wanting on the vomer and palatines. A further
peculiarity is to be found in the presence of a peculiar spiral organ on the fourth
gill-arch ; and the air-bladder differs from that of the other members of the family
in its cellular structure, while the stomach comprises a membranous and a muscular
portion. The fish in question is found alike in the upper Nile and in the rivers of
Western Africa. It grows to about 2 feet in length.



MOON-EYE AND CHISEL- JAW, Families HYODONTID^ and PANTODONTID^;.

Each of the two fishes figured in the annexed illustration is the only represent-
ative not only of a genus, but likewise of a separate family ; these families agreeing




CHISEL-JAW AND MOON-EYE (^ liat. size



with all the remaining ones of the present section in having the pterotic bone
normal, the base of the skull double, and four upper pharyngeal bones, all of which
are distinct, and the third the largest and directed forwards. In the first family
the parietal bones are united, and there are two true tail -vertebra? in front of the
complex bone supporting the rays of the caudal fin.



480 TUBE-BLADDERED GROUP.

Externally, the moon-eye (H>/<></<>i> /V,Y//,S'^.V) ; as the single
representative of the first of the two families is popularly termed, has
the body covered with cycloid scales, the head naked, and no barbels. The margin
of the upper jaw is formed by the premaxillae in front and the maxilla; at tin- sides,
the latter bones being articulated to the former at the point of junction; and all
the elements of the gill-cover are present. There is no fatty fin, and the short
dorsal is placed in the caudal region, above the fore-part of the longer anal ; the
caudal fin being forked. The gill-openings are wide; the stomach is hors< -shoe-
shaped, the intestine short, and the air-bladder simple; false gills being absent.
In form the body is oblong and compressed, with a part of the lower surface form-
ing a sharp edge ; and the cleft of the mouth is somewhat oblique ; all the bones of the
palate bearing small teeth, and the edges of the tongue carrying a larger series.
Before their exclusion, the eggs fall into the cavity of the abdomen. The moon-
eye, shown in the lower figure of the cut on p. 479, grows to a length of from
1 foot to 18 inches, and is confined to the fresh waters of North America, where
it is abundant in the lakes and rivers of the western side of the continent.

The small fish (Pantodon buckholzi) represented in the upper

figure of the cut on p. 479, was discovered not very many years ago in

the rivers on the West Coast of Africa, and takes its name from the strong dental







BEAKED SALMON (J nat. size).

armature of the jaws. Remarkably like a cyprinodont in external appearance,
this fish has the body covered with relatively large scales, and the sides of the head
with bony plates ; the margin of the upper jaw being formed in front by the united
premaxillse, and at the sides by the maxillae. The short dorsal fin is situated stil
further back than in the last genus, its front margin being considerably behhx
that of the rather longer anal; both the pectoral and pelvic fins are very tall, tin
rays of the latter forming isolated filaments, and the caudal is long and pointed,
with some of its rays projecting. The muz/le is blunt, and the cleft of the month
directed upwards. In the gill-cover there is only an opercular and a preopercular
bone, the gill-openings are wide, and the branch lost cgal rays arc numerous.
False gills are absent,; the air-bladder is simple: and the ovaries of the female,
and the corresponding organs of the opposite sex, are furnished with a duct.



BEAKED SALMON. 481

THE BEAKED SALMON, Family GONORHYNCHID^E.

A third fish of the present section, constituting a family by itself, is the so-
called beaked salmon (Gonorhynchus greyi) from the seas of the Cape, Japan, and
Australia. Agreeing with the two preceding families in the absence of a fatty fin
this fish differs in having barbels to the mouth, while in the tail there is no true
caudal vertebra. Both the head and body are completely covered with scales, of
which the free edges are spinose ; and the margin of the upper jaw is formed entirely
by the short premaxillae, which are continued downwards over the maxillae. The
short dorsal fin is situated far back on the body, above the pelvic pair, the still shorter
anal having a more posterior position; and the tail-fin is slightly forked. The
gill-openings are narrow, the air-bladder is wanting, and the stomach simple.
Measuring from 12 to 18 inches in length, this fish seems to be partly pelagic
and partly littoral in its habits ; being found in New Zealand, where it is known
as the sand-eel, in bays with a sandy bottom, while elsewhere it has been taken
in the open sea. In New Zealand its flesh forms an article of food. The family
is also represented by an extinct genus (Notogoneus) from the Eocene of the
United States.

THE SCOPELOIDS, Family SCOPELID^:.

;As an example of an important family of, for the most part, pelagic or deep-
a fishes, we select the so-called phosphorescent sardine, Scopelus engraulis, as
being a member of the typical genus. The members of this family agree with the
last in having the parietal bones united and no true tail-vertebra, but they may
be distinguished externally by the absence of barbels and the presence of a small
fatty fin some distance behind the dorsal, and likewise by the want of spines on
the scales, when the latter are present ; some genera having the body scaled, while
in others it is naked. The margin of the upper jaw is always constituted solely by
the premaxillse ; the gill-cover may be incompletely developed ; the gill-opening is
wide ; false gills are present ; but an air-bladder is wanting. The intestine is
markable for its shortness ; and the eggs are enclosed in the sacs of the ovaries,
hence they are extruded by means of ducts. Containing a large number of
xisting genera, the family is likewise represented by several extinct types, the
arliest of which dates from the Cretaceous of Istria.

In the typical genus the body is oblong in form and more or less markedly
compressed, with the investing scales of large size. Along the sides run series of
phosphorescent spots; while similar glandular structures may in some species
occur on the front of the body and on the back of the tail. The cleft of the
mouth is unusually wide ; the prernaxillary bones being long, slender, and tapering,
and the maxillge well developed. The teeth are villiform, and the eye is relatively
large. The pelvic fins are inserted just in front of or immediately below the line
of the foremost rays of the dorsal (which is situated nearly in the middle of the
length of the body), and are composed of eight rays ; the fatty fin is very small ;
the anal is generally long ; and the caudal forked. There are from eight to ten rays
in the branchiostegal membrane. Dr. Giinther writes that " the fishes of this genus
are small, of truly pelagic habits, and distributed over all the temperate and
VOL. v. 31



482



TUBE-BLADDERED GROUP.



tropical seas; they are so numerous that the surface-net, when used during a
night of moderate weather, scarcely ever fails to enclose some specimens. They
come to the surface at night only ; during the day, and in very rough weather,
they descend to depths where they are safe from sunlight or the agitation of the
water. Some species never rise to the surface ; indeed, scopeli have been brought
up in the dredge from almost any depth to two thousand five hundred fathoms."
Upwards of thirty species of this genus arc known, and there is also an allied
genus (Gymnoscopelus) distinguished by the absence of scales.

Among several other remarkable forms of the family, we may especially
notice a very curious fish (Ipnops) obtained at great depths during the voyage of the




PHOSPHORESCENT SARDINE (liat. size).

Challenger. Possessing an extremely elongate and cylindrical body, covered with
large, thin, deciduous scales, this fish has a depressed head and an elongate, broad,
spatulate muzzle, of which the whole upper surface is occupied by a luminous or
visual organ, divided longitudinally into two halves, and representing the highly-
modified eyes. The whole length of this strange fish does not exceed between 5
and 6 inches. Another deep-sea fish (Plagyodus) is noteworthy on account of
its large dimensions, and the formidable armature of its mouth ; the scaleless body
being long and compressed, the snout much produced, and the teeth of the jaws
and palate of very unequal size, some forming long and sharply-pointed tusks.



THE PHOSPHORESCENT SCOPELOIDS, Families STERNOPTYCHID^:
and STOMA TETDJE.

More or less nearly allied to the scopeloids are two families of deep-sea or

pelagic fishes usually bearing phosphorescent organs along tho sides of the body ;

an example of each being represented in the accompanying illustration.

Silvery Light- The fish (PJtol ir/itlii/s 'arg&nteus) shown in the upper figure of the

Fish. illustration, is taken as our representative of the first of the two

f;m lilies, of which, in addition to the phosphorescent organs, the Ir.-iding characters

are as follows. The body may be either covered with thin deciduous scales, or



PHOSPHORESCENT SCOPELOIDS.



483



entirely naked ; barbels are wanting ; and the fatty fin is either rudimental or of
very minute size. Both the premaxillse and maxillae take a share in the formation
of the margin of the upper jaw, and bear pointed teeth of variable length. The
bones of the gill-cover are not fully developed ; the gill-opening is of great width ;
false gills may or may not be developed ; and, when present, the air-bladder is of
simple structure. The ovaries are furnished with ducts. Whereas in the figured
species the teeth are small, in the allied genus Chauliodus they are greatly
elongated, and thus indicate highly predaceous habits on the part of their owner.
Hedgehog- The members of the second family, of which the bearded

Mouths. hedgehog-mouth (Echiostoma larbatum), shown in the lower figure
of our illustration, is taken as an example, may be readily distinguished from the







SILVERY LIGHT-FISH, AND BARBED HEDGEHOG-MOUTH (| nat. size).

ceding by the presence of a long barbel to the hyoid ; the skin being either
naked or covered with exceedingly delicate scales, and the fatty fin (as in the
figured specimen) frequently wanting. In other characters these fishes closely
resemble those of the preceding family. When a fatty fin is present, as in the
genus Astronesthes, the rayed dorsal is of considerable length, and placed in
advance of the anal; but in the other genera both the anal and dorsal are short, and
placed opposite to one another a short distance in advance of the forked caudal.
In the genus represented by the figured species, the body is naked and the pectoral
fins are filamentous ; but in the allied Stomias there are exceedingly small scales
which scarcely overlap one another. Occasionally met with floating in a helpless
condition, these fishes have been dredged from depths of eighteen hundred fathoms ;
and it will not escape the notice of the reader that, although dwelling in total
darkness, they, like most of their allies, have well-developed eyes. On this point,



TUBE-BLADDERED GROUP.

Monsieur Filhol writes that " the existence of eyes in fishes which we believe to
live in a dark medium, seems at first sight impossible to understand. But this fact
receives an explanation when we learn that the creatures furnished with these
organs are covered with a coating of luminous mucus, or bear phosphorescent
plates. The phosphorescence with which the fishes of the ocean depths are endowed
serves indeed both to guide them and to attract their prey, filling for them in the
latter case the same office as a torch in the hand of a fisherman. This peculiarity
has been long noticed in surface-fishes which pursue their prey at night; Bennett,
for instance, having described a shark which gives off' a bright green phosphor-
escence from the lower surface of its body. On one occasion that zoologist
brought into a room a freshly-caught specimen of this shark, upon which the
whole chamber was illuminated with the light given off from its body. It is
probable that the different species of sharks living at moderate depths, like the one




THE DORAB (^ uat. size).

described by Bennett, make use of their luminosity solely for the purpose of
attracting their prey within reach. In most cases the origin of this light-giving
mucus must be attributed to glandular organs distributed along the flanks and tail,
on the head, and more rarely on the back. There exists, however, in certain fishes,
which lack these glandular organs, an apparatus of a totally different nature for
the emission of light; this apparatus consisting of a kind of biconvex transparent
lens closing the front of a chamber filled with clear fluid. This cavity is carpeted
by a blackish membrane, formed of hexagonal cells, thus recalling the retina of the
eye, and is connected with certain nerves. Phosphorescent plates of this type
may be situated either beneath the eyes, or on the sides of the body," one of the
fishes thus furnished belonging to the family now under consideration, in which it
forms the genus Malacosteus. A specimen of this fish captured before death had
ensued was observed to emit a yellowish light from the uppermost plate beneath
the eye, while that from the lower plate had a greenish tinge. In the genus
Stomias, continues our author, " the sides of the body present a double longitudinal
series of phosphorescent plates, which emit light in such a manner as to cause the



DOKAB.



485



whole fish to be bathed in a brilliant luminous halo. This fish must, indeed, be a
formidable creature to the other inhabitants of the ocean abysses ; being in every
way constructed and armed for strife, and its powerful teeth admirably fitted
to seize and tear the flesh of the other fishes upon which it preys." In other
species (e.g. Eustomias) the barbel is greatly lengthened, all the fins form long
dentated filaments; the whole of these structures being apparently modified for
the emission of phosphorescent light. In our figured species not only are there
luminous dots down the sides of the body, but also larger plates beneath the eyes.

THE DORAB, Family 'CHIROCENTRID^E.

With the fish represented in the accompanying illustration, which ranges
from the Red Sea to the Malay Archipelago, and is commonly known in the East
as the dorab (Chirocentrus dorab), we come to the first of what we may term the



LONG-FIXNED HERRING (f liat. Size)




erring and salmon group, the more typical members of which differ from the
preceding families of this section in having the parietal bones of the skull separated
from one another by the intervention of the supraoccipital. In common with the
herrings, this fish, which is the sole representative of its family, has but a single
true tail-vertebra. Externally the body is covered with thin deciduous scales;
barbels, and a fatty fin are alike lacking ; but the elements of the gill-covers are
fully developed. The margin of the upper jaw is formed partly by the premaxillse
and partly by the maxilla, which are firmly welded at their junction ; the short
dorsal fin is situated in the caudal region of the vertebral column above the much
longer anal, the tail is deeply forked, the pelvic fins are minute, the lower
surface of the body is sharp, the gill-opening wide, and false gills wanting. The
upward direction of the cleft of the mouth, which is armed with formidable teeth,
coupled with the elongation of the lower jaw, gives a rather peculiar expression to
the head, and the eyes are remarkable for being covered with skin. The stomach
is furnished with a blind appendage, the intestine is short, and the air-bladder
cellulated. As this fish attains a length of fully a dozen feet it is a sufficiently
formidable monster, and when captured is said to bite viciously at every object



486 TUBE-BLADDERED GROUP.

within reach. Its flesh is of poor quality. It has been considered that the extinct
Chiromystus, from the Eocene of Brazil, may belong to this family.

LONG-FINNED HERRING, Family BATIIYTHRISSID^:.

Although its osteology has not apparently been described, we may place here
the fish (Bathythriwa dorsalis) shown in the illustration on p. 485, which is
another of the numerous forms in the present section representing a family by
itself. Having an oblong body, with a rounded under surface, invested with
cycloid scales, the head naked and devoid of barbels, and no fatty fin, this fish may
be at once recognised by the great length of the many-rayed dorsal fin, which
occupies nearly the whole length of the back, and is situated in advance of the
short anal. There is no air-bladder, and very small eggs are produced by the
ductless ovaries. This fish, which attains a length of two feet, has been obtained in
Japanese waters at a depth of between three and four hundred fathoms.

THE EXTINCT SAURODONTS, Families ENCHODONTID.E,



Online LibraryRichard LydekkerThe new natural history (Volume 5) → online text (page 51 of 62)