Richard Lydekker.

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latter have no such accessory organs, and evidently only see by the aid of phos-
phorescence. In the greatest depths occur blind fishes, with rudimentary eyes, and
without special organs of touch. Many fishes, of the deep sea are provided with
more or less numerous, round, shining, mother-of-pearl-coloured bodies, embedded
in the skin. These so-called phosphorescent or luminous organs are either bodies of
an oval or irregularly elliptical shape placed in the vicinity of the eyes, or smaller
globular bodies arranged symmetrically in series along the sides of the body and
tail." That the function of these bodies is to produce phosphorescent light may be
considered certain; and it is probable that both the tentacles and the whole surface
of the bodies of these extraordinary fish are also phosphorescent. Not the least
remarkable feature about the carnivorous deep-sea fishes is the enormous size of
their stomachs, which enable them to swallow creatures nearly as large as them-
selves; drawing themselves over their prey almost after the manner of a sea-
anemone. Although when brought to the surface deep-sea fishes are soft, flabby
creatures, with their scales standing out at right angles, and their eyes starting
from their sockets, at their own proper level, under an enormous pressure, their
bodies are doubtless as firm and compact as those of ordinary fish. ])eep-sea fish
certainly live at a depth of two thousand seven hundred and fifty fathoms.

In regard to geological distribution, it has already been mentioned that the
oldest true fishes occur in strata of upper Silurian age; such early fishes being
sharks. In the succeeding Devonian and Carboniferous periods, the class Mas
abundantly represented, but only by sharks, fringe-finned ganoids, and lung-fishes.
In the Permian, Triassic, and Jurassic periods chimseroids, as well as the
chondrosteous Teleostomi made their appearance; but it was not till the
Cretaceous epoch that the higher bony fishes, which are the predominant forms in
the Tertiary period and at the present day, were developed. There are fully nine
thousand known species of living fishes, while considerably more than one thousand
fossil forms have been already described




THE two first subclasses of fishes agree with one another, and thereby differ from
the remaining two, in the structure of the skull, in which the hyomandibular bone
is welded with what is known as the palatopterygoid bar (that is to say, the bones
corresponding with the palatines and pterygoids of the higher Vertebrates), which
is itself firmly united to
the cranium proper, so
that there is no separate
structure for the suspen-
sion of the lower jaw.
To this type the name of
solid-skulled (technically,
autostylic) fishes may be
applied ; and it may be

noted that this type of B If >fA ^ . /'A,M -4i~- orb.

structure is essentially the
same as that on which the
skulls of the Amphibians
are formed. In the lung-
hes the skeleton is par-
tially ossified, with well-
developed membrane-
hoiies; the gill-clefts are
but slightly separated, and
open into a single cavity
protected by an external
cover; and the external
skeleton consists of true
bony tissue. In the
existing members of the
roup the optic nerves (or
those proceeding from the
brain to the eyes) simply
ross one another, without any interlacing of the constituent fibres; the intestine
has a spiral valve ; the air-bladder is elongated, and performs the functions of a
lung ; and the nostrils open posteriorly by two apertures into the cavity of the


A. anterior, and B, posterior median plate ; C, inner, and D, outer lateral
plate ; na. nostrils ; orb, socket of the eyes. (From Teller.)



mouth, after the manner of the higher Vertebrates. The membrane-bones covering
the roof of the skull, which are very few in number, cannot be correlated with
those of the bony fishes; their mode of arrangement heing .shown in the accom-
panying figure. The lung-fishes are at the present day represented only by three
genera, with but very few species, but they were formerly a very numerous group,
which appears to have been on the wane since a very early epoch.


The three existing genera of lung-fishes may be taken as the typical repre-
sentatives of an order including several extinct families, and known as the
Sirenoidea. Its essential characters are that the head is covered with membrane-
bones; that the main dentition takes the form of large grinding plates, situated on


the pterygoid bones in the upper, and on the splenials in the lower jaw; that tin
body is covered externally with overlapping scales; that the notochord persists
throughout life ; that the paired fins are of the fringed type ; and that none of the
fins are armed with spines. The existing forms have but few membrane-bones t<
the skull; no premaxillse, maxillae, marginal teeth, or jugular plates; a fringe/
tail, furnished with a continuous vertical fin ; and cycloid scales.

Australian For a great number of years there were known from the Triassi<

Lung-Fish, strata of various parts of Europe fish-teeth of the remarkable typ<
of the specimen represented in the accompanying figure ; and from the fanciei
resemblance to a deer's antler, presented by these teeth, the name of Ceratodus was
suggested for the otherwise unknown fishes to which they pertained. Similai
teeth were subsequently obtained from Secondary rocks in India and also in South
Africa, but it was not until the year 1870 that a fish was discovered in Queensland
having teeth of a similar type. Known to the natives, in common with other large
fresh-water species, by the name of barramundi, the Australian lung-fish (C.forxlr
agrees so closely with the extinct forms that it is usually regarded as genericalh
identical. Its mouth is furnished in front with a pair of chisel-like teeth situate.
on the vomers, behind which come a pair of palatal teeth of the type of the on.
shown in the figure, but carrying six complete ridges, and an incomplete seventh


3 2 7

while there are a pair of similar teetli in the lower jaw, carrying- only six ridges
each. In the living species the teeth of opposite sides are separated by an interval ;
]ufc in the fossil forms they were in contact, and had fewer ridges. The existing
Australian lung- fishes, of which two species have been described, are said to
attain a weight of 20 Ibs., and a length of upwards of 6 feet. The body is
elongated and much compressed, with very large scales ; the paddle-shaped limbs
have very broad fringes ; and the flesh is salmon-coloured. From the occurrence
of masses of leaves in its stomach it is evident that the Australian lung-fish crops
the vegetation with its great teeth ; but it is believed that the most important part
of its food consists of the small creatures living on and between the leaves of the

liat. size).

various water-plants. The stories of the fish coming out of the water to the land
seem quite unfounded, as are those that it lies dormant during part of the year in
cocoons. The female lays her rather large eggs loosely and singly among the
vegetation, and in the embryo the fore-limbs make their appearance in about a
fortnight, but the hinder-pair not before two and a half months. In the course of
its development this fish presents marked resemblances to the Amphibians, and also
to the lampreys ; but it is noteworthy that there is no trace of a sucking mouth,
01- of external gills. As might have been inferred from the study of allied extinct
forms, the large palatal teeth are formed by the fusion of a number of separate
small teeth. According to Dr. Semon, the Australian lung-fish is confined to the
middle portion of the Burnett and Mary Kivers of Queensland. Living among the



mud and leaves at the bottom, it rises at intervals to the surface to obtain more
complete oxygenation of its blood by the inhalation of atmospheric air into its
lungs, although its general breathing is carried on by the gills. A grunting noise
sometimes uttered by this fish is probably produced by the expulsion of the air
from the lungs when it rises to the surface. Although frequently termed the
barramundi a title apparently properly belonging to a totally different fisli
(OxfwHjluKKtmi) it appears that the proper native name of the Australian lung-fish
is djelleh. The breeding-season is at its height in September and October, but
lasts from April till the beginning of November ; and the eggs, which arc enveloped
in a gelatinous coat, and are heavier than water, take some ten days to hatch,
south American. The mud-fish of the Amazons (Lepidosiren paradox^) is the sole
Mud-Fish. representative of a genus distinguished from the last by the eel-like
form of the body, on which the continuous vertical fin extends nearly to the neck,
and by the reduction of the limbs to mere tapering filaments, owing to the dis-


appearance of the marginal fringe. The vomerine teeth are conical and pointed,
and the palatal teeth have strongly marked cusps supported by vertical ridge ^
There are five gill-arches, with four intervening clefts, but there are no extern;
appendages above the gill-opening. In adult males the upper surface of the hind-
limb is beset with tufts of tentacle-like papilla?. This mud-fish grows to a length
of about 4 feet, and occurs not only in the Amazon and its tributaries, but likewise
in the swamps of the Chako country forming the tributaries of the upper Paraguay
River. The southern form has been regarded as a distinct species, although the
differences are so slight, as scarcely to merit such a distinction. These fish feed
chiefly on the large molluscs known as ampulla ria>, which are found collected in


3 2 9

great masses in the Chako swamps; their shells being easily crushed by the power-
ful teeth of their devourers.

The African mud-fish (Protopterus annectans). widely spread
African Mud Fish. J

over the tropical regions of the continent from which it takes its

name, differs from the last in that the filamentous fins retain a small fringe
containing rays ; as well as in having six gill-arches, with five intervening clefts,
while there are three small tentacle-like appendages above the small gill-opening
on each side. In the Gambia River, where they are very abundant, these fishes
are in the habit of burying themselves during the dry season, making a kind of

AFlUt'AN MUD-FISH (\ liat. size).

nest, in which they pass a period of torpidity. Here they may remain for the
greater part of the year, only resuming their normal aquatic life with the return
of the wet seasons. Professor W. N, Parker, who received some specimens in the
torpid condition, writes that about a hundred individuals were dug out and packed
up in crates still enclosed in the clods of mud. On arrival in Europe the clods
were opened, and the fishes placed in a tank in a hothouse. The statement of the
natives that the species grows to the almost incredible length of 6 feet suggests
that it must be a very long-lived creature. From the above-mentioned specimens
it was found that these mud-fishes grow very rapidly, have great vitality, and,
although able to sustain fasts, are exceedingly voracious, devouring all the snails,


earth-worms, and small fish <riven them, and then killing and eating eacli other,

* O CJ O

Making- it difficult in the extreme to preserve the .specimens. Tliey arc most
active at night, and appear to keep mostly to the shallow water, where they move
deliberately about on the bottom, alternately using the peculiar limits of either
side, though their movements do not seem to be guided by any strict regularity.
Gray has compared these movements to those of a newt, and several other
observers have noticed them. The powerful tail forms a most efficient organ for
swimming rapidly through the water. It is well known that this fish comes to
the surface to breathe at short intervals, and thus it is evident that the lun^s

' ~

perform an important, if not the chief, part in respiration during the active life of
the animal. The air passes out again through the opercular aperture, and the
movements of the operculum itself indicate the fact that bronchial as well as
pulmonary respiration takes place. Externally, the sexes present no characters
whatever distinguishing them apart. As in the American species, external gills
are developed in the young. As regards the breeding-habits of these fishes nothing
very definite is known. It is stated, however, that the numerous eggs and embry< >s
are carried about in an elongated gelatinous pouch attached to the sides of the
back of one of the parents, although the sex in which these receptacles are developed
does not appear to have been ascertained. In conclusion, it may be observed that
Professor Parker is of opinion that although the lung-fishes present certain
resemblances on the one hand to some of the sharks and ganoids, and on the other
to the lower Amphibians, yet they appear so distinct from both that he thinks
they ought to be removed from the fishes to form a class by themselves.

Extinct In the Palaeozoic epoch lung-fishes formed an abundant group,

Lung-Fishes. wn ich may be divided into three families. Of these the Carboniferous
and Permian Ctenodontidce, as represented by Ctenodus and Sagenodus, resemble
the existing forms in the absence of marginal teeth to the jaw and of jugular
plates on the throat, but differ by the numerous membrane-bones of the skull ; the
caudal fin being of the fringed type, and the scales cycloidal. The type genus,
which includes species of 5 feet in length, takes its name from the comb-like
structure of the ridged palatal teeth. The second family, Phaneropleurida', differs
from the last in the presence of both marginal teeth and jugular plates ; the
typical genus Phaneropleurum, including small species from the Devonian. In
the Dipteridas, as represented by the Devonian Dipterus and Paki'(I<i/>lnt*, jugular
plates are present, but there are no marginal teeth, and the tail is of the hetero-
cercal type; the skull having numerous membrane-bones. The teeth are very
similar to those of the Australian lung-fish, but may be ornamented with small
ridges and pustules.


The extraordinary Palaeozoic group typically represented by the berry-bone
fish (Coccosteus) of the Scottish Devonian differs from the true lung-fishes in that
in place of scales the fore-part of the body is protected by large bony plates, of
which one pair is articulated by a hinge to the hinder-part of the skull, which is
likewise invested with bones bearing a similar pustular, or berry-like sculpture.


rudimental or wanting;

but a pair of pelvic fins Avert-
included in the .single family


(From A. S. Woodward, Cat. Foss. Fishes, Brit. Mus.)

The fore-limbs were either
i|c\ ('loped. Most or all of the forms may
Coccosteidcu ; and
;i 1 1 long these the
typical genus is dis-
tinguished by the
absence of any
pectoral fin, while in
the allied Krachy-
d'lfiiK this appendage
represented by a

)ll<m r spine. In both these the sockets of the eyes form notches on the sides
the skull; and the same is the case with the gigantic Dmichth.ys of the North
ican Devonian. In another group, however, as represented by Homosteus, the
'e-sockets were completely enclosed in the membrane-bones with which the head

THE CHIIVLEROIDS, Subclass Holocephali.

Represented by three existing marine genera, of which one has three, the second
le, and the third two species, and a number of extinct types, the chimaeroids form
second subclass, agreeing with the lung-fishes in their solid (autostylic) skulls,
it (littering by the total absence of membrane-bones, and their superficial external
semblance to sharks. The skeleton is cartilaginous, with the notochord either
irsistent. or constricted and surrounded by cartilaginous rings, which are some-
nes partly calcified ; and in the adult the skin is frequently quite naked, although
the young it may bear on the back a series of structures similar in composition
teeth, some extinct forms having plates of the same nature. In the existing
icmbers of the group the optic nerves simply cross one another, and the intestine
has a spiral valve ; while further resemblances to the sharks are shown by the
3sence of claspers in the males, and also by the large size and small number of
single eggs, The four gill-clefts open externally by a single aperture on each
le, protected by a fold of skin containing a cartilaginous operculum. The mouth
situated at the extremity of the muzzle, and the teeth on the palate and lower
jaw are molar-like, while there is also a small pair of cutting vomerine teeth in the
front of the upper jaw; the whole dentition thus closely corresponding to that of
the lung-fishes, although there are two pairs of upper palatal teeth, which present
certain hardened areas known as tritors. The pectoral fins are shortened, without
the segmented axis of the lung-fishes ; and the first dorsal fin may have a movable
spine articulated to the spinous processes of the vertebra?. The sides of the body
show a lateral line; but there is no air-bladder, and the nostrils do not open
behind into the cavity of the mouth. It has been suggested that the chimseroids
indicate a degenerate group nearly allied to the lung-fishes, which have lost the
membrane-bones of the latter, and acquired a superficial resemblance to sharks.

The ugly fish, to which the name chimaera has been applied (Ckimo-rd,
monstrosa), together with two other existing species, typically represents the
family dhi'iiiccridcu, which alone has survived to the present day. The family is


characterised by the presence of a spine to the first dorsal fin, and also of a
prehensile spine-like structure on the heads of the males ; there are no superficial
plates on the skull, and only a single pair of lower teeth. The family, which
contains a number of extinct gertera, mainly distinguished from one another by
the characters of the triturating areas on the teeth, dates from the Lias ; the
typical genus being, however, unknown before the latter part of the Tertiary
period. The living chimaeras do not probably exceed 5 feet in length, and have
the soft muzzle devoid of an appendage. The dorsal fins occupy the greater part
of the back ; and the longitudinal axis of the long filamentous tail is nearly
continuous with that of the back, its extremity being provided above and below
with a long, low fin of the diphycercal type. The common species represented
in the annexed coloured Plate ranges from Europe and Japan to South Africa ;
while a second occurs on the Pacific Coast of North America, and a third off
Portugal. The southern chimsera (Cattorhynchua antarcticus), from the southern
temperate seas, differs from the preceding genus by the presence of a cartilaginous
prominence, ending in a flap of skin, on the muzzle, and likewise by the upward
direction of the extremity of the tail, which has no fin on its upper surface. A
fossil representative of this genus occurs in the Cretaceous rocks of New
Zealand. The third genus, Harottia, distinguished by the extreme elongation of
the snout, is represented by one species from the Atlantic, and a second from
the Pacific. As well-known extinct types of the family we may refer to the
Cretaceous and Tertiary genera Edapliodon and Elasmoclus ; the former including
fishes of gigantic dimensions. The members of the extinct family Mi/rid-
canthidcB, of the Jurassic rocks, differ by having a few bony plates on the head,
and three lower teeth ; while the Squaloraiidcv, as represented by Squaloraia of
the Lias, were somewhat ray-like forms, with a depressed trunk and elongated
muzzle, and no spines to the dorsal fins. The subclass appears also to be repre-
sented in Palaeozoic times, the Devonian Ptyctodus indicating a family which
cannot at present be fully defined.




FORMERLY the typical bony fishes of the present day were regarded as indicating a
primary group (Teleostei) of equal rank with a second one known as the Ganoidei ;
the latter containing the American bony pike, and the African bichir, together
with a host of extinct genera possessing a similar armour of hard ganoid scales.
A fuller study of these and other allied fossil forms has, however, shown the
existence of such a complete transition from these so-called ganoids to the typical
bony fishes that it has become necessary to include the whole of them in a single
subclass, under the title heading this chapter. Although there is still some degree
of uncertainty as to the best mode of arranging certain groups of the bony fishes,
the following scheme may be temporarily adopted :

1. Order ACTINOPTERYGII Fan-Finned Group.

(1) Suborder., fAcANTHOPTERYGii Spine-Finned Fishes.

(2) | LOPHOBRANCHII Tuft-Gilled Fishes.

(3) i I PLECTOGNATHI Comb-Gilled Fishes.

(4) ., [ANACANTHINI Soft-Finned Fishes.

(5) PHYSOSTOMI Tube-Bladdered Fishes,

(6) ISOSPONDYLI Leptolepis.



(9) CHONDROSTEI Sturgeons.

2, Order CROSSOPTERYGII Fringe-Finned Group.

In this wide sense the subclass differs broadly from the two preceding ones in
le structure of the skull, which is formed on what may be termed the hinged type
iyostylic); .that is to say, the palato-pterygoid bar remains separated from the
cranium proper, to the hinder-part of which it is movably articulated by the
intervention of the hyomanclibular. The internal skeleton is more or less ossified,
with the development of membrane-bones on the jaws ; the gill-clefts are but
slightly separated from one another, and are fully protected by an operculum ; the
membrane-bones of the pectoral girdle (that is to say, the scapula, claviculars, etc.)
are connected witli the hinder-part of the skull ; and the external skeleton takes
the form either of plates of bone or of calcified overlapping scales. In existing
forms the eggs are small, numerous, and generally massed together; the two optic
nerves may either simply cross one another, or may give off mutually interlacing
fibres ; an air-bladder with or without a duct is very generally present ; and the
intestine may sometimes be furnished with a spiral valve.



Fan-Finned This group Actinopterygii includes all the bony fishes of tin-

Group, present day, as well as the sturgeons, and is characterised by the
fan-like structure of the paired fins, in which the proper internal skeleton is
abbreviated to make way for the greatly developed dermal fin-rays; the caudal
fin being of very variable structure. In the branchiostegal membrane, occupying
the space between the two branches of the lower jaw, there is always a paiivd
series of transversely elongated rays. The first eight suborders of this order, given
in the table on p. 333, form one great division characterised by the number of
dermal rays in the dorsal and anal fins being equal to that of the supporting


bony elements, and by the tail being never heterocercal, 1 but usually either of the

abbreviate-heterocercal or homocercal type, although occasionally diphycercal.

spine-Finned In the classification proposed by Professor Cope the first four

Fishes. suborders of the fan-finned group given in the foregoing table are

regarded as a single group, under the title of Physoclysti, and, in common with

the tube-bladdered fishes, have the fibres of the optic nerves interlacing, the intestine

without a spiral valve, and the skeleton fully ossified. From the Physostomi. the

1 In the heterocercal type the upper lobe of the tail is tin- longer, and the TertebnJ column is continued up
info it; in tin- abbrevUte-beterocerc*] tin- tail is symmetrical, and tin- vertebral column complete but Lent u]>
into its upper half ; in the homocercal type the tail is also symmetrical, but tin- vertebra ship short at it-
where the latter ones are aborted into a mass ; in the diphycercal form the vertebrae are continued without abortion

Online LibraryRichard LydekkerThe new natural history (Volume 5) → online text (page 35 of 62)