Teleost

“ The characteristics of the order are an osseous or bony skeleton; gills protected by a gill cover or operculum; and an equally divided tail. Lowest among the Teleosts is the common eel. It has an elongated, cylindrical, thick-skinned body, and is destitute of ventral fins. There are many species, and they are widely distributed, living in both salt and fresh water. One species is electrical. ”

“ They do not really fly, as they have not muscular power in their fins to beat the air as birds do. But when extended the fins help bear them up, and the impulse received at the start, sufficient to give them the elevation they reach, may be supplemented by the use of the caudal fin as in swimming. Some naturalists claim to have noticed a movement of the other fins, but the preponderance of testimony is that these are of service only as parachutes or the wings of a paper kite. The Herring, Shad, Salmon, Pike, Perches, Bass, Mackerel and Cod are valuable food fishes, belonging to the Teleosts. ”

“ The richness of the neighborhood in deep-water forms has been well known since the studies of the Challenger. Glass sponges of many species are frequent prizes of the fishermen. And stalked crinoids (Metacrinus rotundus) are often taken off the reef Okinosé. Among the fishes Bathythrissa, a primitive deep-water teleost, of which the Challenger was able to obtain but few examples, is now taken off Misaki so abundantly that it is regularly shipped to the fish-market in Tokyo. ”

“ On this interpretation the condition characteristic of Teleosts would be due to the lips of the oviduct becoming fused with the ovarian wall, and the duct itself would be a Müllerian duct as elsewhere.
A departure from the normal arrangement is found in those Teleosts which shed their eggs into the splanchnocoele, e.g. amongst Salmonidae, the smelt (Osmerus) and capelin (Mallotus) possess a pair of oviducts resembling Müllerian ducts while the salmon possesses merely a pair of genital pores opening together behind the anus. ”

“ A continuous median fin-fold occurs also in various Teleosts (many deep-sea Teleosts, eels, &c.) , though the highly specialized features in other respects make it probable that we have here to do with a secondary return to a condition like the primitive one. In the process of segmentation of the originally continuous fin-fold we notice first of all a separation of and an increase in size of that portion of the fin which from its position at the tip of the tail region is in the most advantageous position for producing movements of the body. There is thus formed the caudal fin. ”

“ Scarcely less brilliant is the coloration of those Teleosts, notably species of Pomacentridae and Chaetodontidae, which frequent the coral reefs of the East Indian Archipelago and the Pacific and feed on the coral polypes, and of many of the Wrasses (Labridae) . Many other groups, such, for example, as the Percidae, Cirrhitinae, and the Pipe-Fishes (Syngnathidae) , include species in which the coloration is vivid and often beautiful, although less striking than is the case with the Fishes mentioned above. ”

“ The earliest of the true bony fishes or teleosts appear in Mesozoic times, the most primitive forms being soft-rayed fishes with the vertebræ all similar in form, allied more or less remotely to the herring of to-day, but connected in an almost unbroken series with the earliest ganoid forms. In these and other soft-rayed fishes the pelvis still retains its posterior insertion, the ventral fins being said to be abdominal. The next great stage in evolution brings the pelvis forward, attaching it to the shoulder-girdle so that the ventral fins are now thoracic as in the perch and bass. ”

“ The Fishes included in the Teleostomi were formerly arranged in two groups: the Ganoidei, including the Crossopterygii, Chondrostei, and the Holostei, with their numerous fossil allies; and the Teleostei. Living Ganoids agree with one another, and differ from Teleosts in possessing an intestinal spiral valve and a conus arteriosus. It is difficult, however, to separate the two groups, inasmuch as in each group there are living forms which tend to approximate to the other; and numerous fossil genera, of whose soft parts nothing is known, are in many respects intermediate between the two. ”

“ Secondary sexual characters are best marked in Teleosts, where they are generally related to the special rôle which each sex takes in the deposition and fertilisation of the eggs, and the nurture and protection of the young, of which examples have already been given. To a more limited extent they may be associated with the struggle of the males for the females, and in at least a few Teleosts the exuberant coloration of the males in the breeding season suggests that instances of courtship and sexual selection are not altogether wanting. ”

“ Teeth and scales of Lepidotus (with Sphærodus as subgenus) , clearly a freshwater fish, are widely distributed in the Wealden, and finally disappear in the chalk; its body was covered with large rhomboidal ganoid scales. Gyrodus and Aspidorhynchus occur in the beds of Voirons, Coelodus and Amiopsis (allied to Amra) , in those of Comen, in Istria. But the Palæichthyes are now in the minority; undoubted Teleosteans have appeared, for the first time, on the stage of life in numerous genera, many of which are identical with still existing fishes. ”

“ It might have been anticipated that the Teleostean Ganoids would resemble the Teleostei, but, from an examination of adult Teleostei, it would seem to be clear that the relations of the parts are the same as in Elasmobranchii, i.e. that the ribs have no share in forming the hæmal canal in the tail. Aug. Müller and Götte have however brought embryological evidence (though not of a conclusive character) , to shew that in the embryo the ribs really fuse with the hæmal processes in the tail, and so assist, as in the Ganoids, in forming the hæmal canal. ”

“ The absence of pigment is sometimes protective. The surface-swimming larvae of many Teleosts have no chromatophores, and therefore no obvious pigmentary colours. Their bodies are so translucent that they can be seen through, and hence are visible only with difficulty. ”

“ In the Symbranchidæ the gill-openings coalesce into a single narrow slit in the median line of the isthmus. In the majority of Teleosteans the integument of the concave side of the branchial arches develops a series of horny protuberances of various form, the so-called gill-rakers. They are destined to catch any solid corpuscles or substances which would be carried into the gill-cavity with the water. In some fishes they are setiform, and form a complete sieve, whilst in others they are merely rough tubercles, the action of which must be very incomplete if they have any function at all. ”

“ A revolution has [109] occurred among the Fishes. Sharks of modern type are numerous. Crossopterygians and Ganoidei are rare. There has been an immense expansion of Teleosts or Bony Fishes, which now become the dominant fishes. Most of the Cretaceous Teleosts belong to modern families and even genera.
The Reptiles, in this period, continue to be the dominant types of the land, air, and sea, and it is difficult to decide whether the Cretaceous or the Jurassic is to be regarded as the culminating period of Reptilian history. ”

“ In the quasi-parasitic Cyclostome, Myxine, and in many Teleosts belonging to widely different families, which live at great depths in the sea or inhabit subterranean waters, the eyes suffer from disuse and degenerate in structure. The influence of a deep-sea habitat on the eyes of Fishes is somewhat varied. The eyes are often small. ”

“ Passing on next to the Vertebrate Animals of the Cretaceous period, we find the Fishes represented as before by the Ganoids and the Placoids, to which, however, we can now add the first known examples of the great group of the Bony Fishes or Teleosteans, comprising the great majority of existing forms. The Ganoid fishes of the Cretaceous (Lepidotus, Pycnodus, &c.) present no features of special interest. Little, also, need be said about the Placoid fishes of this period. As in the Jurassic deposits, the remains of these consist partly of the teeth of genuine Sharks (Lamna, Odontaspis, &c.) ”

“ Much has been done towards ascertaining the life-histories of the fishes of economic importance, both in Europe and in North America, and our knowledge of the larval and post-larval forms has made great progress.
Wonderful activity has been displayed in the field of palaeontology, and the careful working out of the morphology of the archaic types has led to a better understanding of the general lines of evolution; but it is to be regretted that very little light on the relationships of the living groups of Teleosteans has been thrown by the discoveries of palaeontologists. ”

“ In the Dipnoi, [173] as in Teleosts, the scales are enclosed in dermal pockets, and exhibit a regular, imbricated disposition in oblique rows (Fig. 304, A) . In shape they are nearly cycloid, or slightly oval, with the long axis coinciding with that of the body. Structurally, also, they bear some resemblance to Teleostean scales, although differing in details. On the outer surface of the scales there are numerous small conical spines. ”

“ The Ganoidei and Teleostei (constituting the Actinopteri) are very closely related, the ancient group passing by almost imperceptible degrees into the modern group of bony fishes.
Subclass Crossopterygii.—The earliest Teleostomes known belong to the subclass or group called after Huxley, Crossopterygii (κρόσσος, fringe; πτερύξ, fin) . A prominent character of the group lies in the retention of the jointed pectoral fin or archipterygium, its axis fringed by a series of soft rays. This character it shares with the Ichthyotomi among sharks, and with the Dipneusti. ”

“ The vertebræ have been economically withdrawn from the tail, and the cartilaginous axis of the side fins has been found unnecessary. The air sac has become a swim bladder. In this complete specialization they have long since lost the possibility of evolving into higher types.
It is interesting to note that the modern teleosts in their embryological growth pass through the stages which characterized the maturity of their Devonian ancestors; their skeleton is cartilaginous and their tail fin vertebrated. ”

“ Certain Teleostean families like the Siluridae, the Sciaenidae, and the Triglidae, seem to be distinguished above all others by the {364}prevalence of some form of vocal organ. According to Sörensen, the first mentioned of the three families includes no less than 68 species, which utilise the air-bladder alone as a sound-producing organ. Nevertheless, there still remain many Teleostean families, rich in genera and species, and with an almost world-wide geographical distribution, in which such organs have not yet been found. ”

“ By one or other of these various methods the air-bladder is either known to be sound-producing, or is believed with good reason to be such, in the following Teleosts, [424] and many others:—Certain species of the South-American genera of Siluridae, Pimelodus, Sorubim, Platystoma, Piratinga, Centromochlus, and Trachelyopterus; species of the South-American family Characinidae; Amblyopsis spelaea, the blind Fish from the Mammoth Cave of Kentucky (Amblyopsidae) ; among the Syngnathidae, the short-snouted Sea-Horse (Hippocampus brevirostris) of the British Coasts ”

“ A few Teleosteans show an arrangement similar to that of Chondropterygians and Dipnoi, the urogenital openings being in the posterior wall of the rectum (Symbranchidæ, Pediculati, and some Plectognathi) .
[157]
CHAPTER XII.
ORGANS OF REPRODUCTION.
All fishes are dioecious, or of distinct sex. Instances of so-called hermaphroditism are, with the exception of Serranus, abnormal individual peculiarities, and have been observed in the Cod-fish, some Pleuronectidæ, and in the Herring. Either the generative organ of one side was found to be male, that of the other female ”

“ All the ancient fossil fishes belong to the above-mentioned groups, and many of them have little resemblance to existing forms. The Teleostean fishes, which form the great bulk of those now living, cannot be traced back further than the Cretaceous period, while by far the larger number first appear in the Tertiary beds. ”

“ Tropic, or appear in single species only; and of Teleosteans, the Berycidæ, Pagrus, the Heterolepidina, Cottus and allied genera, Lophius, Anarrhichas, Stichæus, Lepadogaster, Psychrolutes, Centriscus, Notacanthus, the Labridæ and Embiotocidæ, the Lycodidæ, Gadidæ, and marine Salmonidæ disappear either entirely, or retire from the shores and surface into the depths of the ocean.
With regard to variety of forms, as well as to number of individuals, this zone far surpasses either of the temperate zones; in this respect, the life in the sea is as that on the land. ”

“ The eye of Branchiostoma is of the most rudimentary condition. It is simply a minute speck coated by dark pigment, and receiving the end of a short nerve. In Myxinoids the minute rudiment of the eye is covered by the skin and muscles. This is also the case in many of the blind Teleosteous fishes; however, whilst in the former fishes the organ of sight has not attained to any degree of development, the rudimentary eye of blind Teleostei is a retrogressive formation, in which often a lens and other portions of the eye can be recognised. ”