ACANTHOPTERYGII; SYNENTOGNATHI
=ORDER Acanthopterygii, the Spiny-rayed Fishes.=—The most of the
remaining bony fishes constitute a natural group for which the name
_Acanthopterygii_ (ἄκανθα, spine; πτερύξ, πτερόν, fin or wing) may be
used. This name is often written _Actinopteri_, a form equally correct
and more euphonious and convenient. These fishes are characterized, with
numerous exceptions, by the presence of fin spines, by the connection of
the ventral fins with the shoulder-girdle, by the presence in general of
more than one spine in the anterior part of dorsal and anal fins, and as
a rule of one spine and five rays in the ventral fins, and by the
absence in the adult of a duct to the air-bladder. Minor characters are
these: the pectoral fins are inserted high on the shoulder-girdle, the
scales are often ctenoid, and the edge of the upper jaw is formed by the
premaxillary alone, the maxillary being always toothless.
But it is impossible to define or limit the group by any single
character or group of characters. It is connected with the
_Malacopterygii_ through the _Haplomi_ on the one hand by transitional
groups of genera which may lack any one of these characters. On the
other hand, in the extreme forms, each of these distinctive characters
may be lost through degeneration. Thus fin spines, ctenoid scales, and
the homocercal tail are lost in the codfishes, the connection of
ventrals with shoulder-girdle fails in the _Percesoces_, etc., and the
development of the air-duct is subject to all sorts of variations. In
one family even the adipose fin remains through all the changes and
modifications the species have undergone.
The various transitional forms between the _Haplomi_ and the perch-like
fishes have been from time to time regarded as separate orders. Some of
them are more related to the perch, others rather to ancestors of salmon
or pike, while still others are degenerate offshoots, far enough from
either.
On the whole, all these forms, medium, extreme and transitional, may
well be placed in one order, which would include the primitive
flying-fishes and mullets, the degraded globefishes, and the specialized
flounders. As for the most part these are spiny-rayed fishes, Cuvier's
name _Acanthopterygii_, or _Acanthopteri_, will serve us as well as any.
The _Physoclysti_ of Müller, the _Thoracices_ of older authors, and the
_Ctenoidei_ of Agassiz include substantially the same series of forms.
The order _Teleocephali_ of Gill (τελεός, perfect; κεφαλή, head) has
been lately so restricted as to cover nearly the same ground. In Gill's
most recent catalogue of families, the order _Teleocephali_ includes the
_Haplomi_ and rejects the _Hemibranchii_, _Lophobranchii_,
_Plectognathi_, and _Pediculati_, all of these being groups
characterized by sharply defined but comparatively recent characters not
of the highest importance. As originally arranged, the order
_Teleocephali_ included the soft-rayed fishes as well. From it the
_Ostariophysi_ were first detached, and still later the _Isospondyli_
were regarded by Dr. Gill as a separate order.
We may first take up serially as suborders the principal groups which
serve to effect the transition from soft-rayed to spiny-rayed fishes.
=Suborder Synentognathi.=—Among the transitional forms between the
soft-rayed and the spiny-rayed fishes, one of the most important groups
is that known as _Synentognathi_ (σύν, together; ἔν, within; γνάθος,
jaw). These have, in brief, the fins and shoulder-girdle of _Haplomi_,
the ventral fins abdominal, the dorsal and anal without spines. At the
same time, as in the spiny-rayed fishes, the air-bladder is without duct
and the pectoral fins are inserted high on the side of the body. With
these traits are two others which characterize the group as a suborder.
The lower pharyngeal bones are solidly united into one bone and the
lateral line forms a raised ridge along the lower side of the body.
These forms are structurally allied to the pikes (_Haplomi_), on the one
hand, and to the mullets (_Percesoces_), on the other, and this
relationship accords with their general appearance. In this group as in
all the remaining families of fishes, there is no mesocoracoid, and in
very nearly all of these families the duct to the air-bladder disappears
at an early stage of development.
[Illustration:
FIG. 165.—Needle-fish, _Tylosurus acus_ (Lacépède). New York.
]
=The Garfishes: Belonidæ.=—There are two principal groups or families
among the _Synentognathi_, the _Belonidæ_, with strong jaws and teeth,
and the _Exocœtidæ_, in which these structures are feeble. Much more
important characters appear in the anatomy. In the _Belonidæ_ the third
upper pharyngeal is small, with few teeth, and the maxillary is firmly
soldered to the premaxillary. The vertebræ are provided with
zygapophyses. The species of _Belonidæ_ are known as garfishes, or
needle-fishes. They resemble the garpike in form, but have nothing else
in common. The body is long and slender, covered with small scales.
Sharp, unequal teeth fill the long jaws and the dorsal is opposite the
anal, on the hinder part of the body. These fishes are green in color,
even the bones being often bright green, while the scales on the sides
have a silvery luster. The species are excellent as food, the green
color being associated with nothing deleterious. All are very voracious
and some of the larger species, 5 or 6 feet long, may be dangerous even
to man. Fishermen have been wounded or killed by the thrust of the sharp
snout of a fish springing into the air. The garfishes swim near the
surface of the water and often move with great swiftness, frequently
leaping from the water. The genus _Belone_ is characterized by the
presence of gill-rakers. _Belone belone_ is a small garfish common in
southern Europe. _Belone platura_ occurs in Polynesia. The American
species (_Tylosurus_) lack gill-rakers. _Tylosurus marinus_, the common
garfish of the eastern United States, often ascends the rivers.
_Tylosurus raphidoma_, _Tylosurus fodiator_, _Tylosurus acus_, and other
species are very robust, with short strong jaws. _Athlennes hians_ is a
very large fish with the body strongly compressed, almost ribbon-like.
It is found in the West Indies and across the Isthmus as far as Hawaii.
Many other species, mostly belonging to _Tylosurus_, abound in the warm
seas of all regions. _Tylosurus ferox_ is the long tom of the Australian
markets. _Potamorrhaphis_ with the dorsal fin low is found in Brazilian
rivers. A few fossil species are referred to _Belone_, _Belone flava_
from the lower Eocene being the earliest.
=The Flying-fishes: Exocœtidæ.=—The family of _Exocœtidæ_ includes the
flying-fishes and several related forms more or less intermediate
between these and the garfishes. In these fishes the teeth are small and
nearly equal and the maxillary is separate from the premaxillary. The
third upper pharyngeal is much enlarged and there are no zygapophyses to
the vertebræ.
The skippers (_Scombresox_) have slender bodies, pointed jaws, and, like
the mackerel, a number of detached finlets behind dorsal and anal,
although in other respects they show no affinity to the mackerel. The
common skipper, or saury (_Scombresox saurus_), is found on both shores
of the North Atlantic swimming in large schools at the surface of the
water, frequently leaping for a little distance like the flying-fish.
They are pursued by the mackerel-like fishes, as the tunny or bonito,
and sometimes by porpoises. According to Mr. Couch, the skippers, when
pursued, "mount to the surface in multitudes and crowd on each other as
they press forward. When still more closely pursued, they spring to the
height of several feet, leap over each other in singular confusion, and
again sink beneath. Still further urged, they mount again and rush along
the surface, by repeated starts, for more than one hundred feet, without
once dipping beneath or scarcely seeming to touch the water. At last the
pursuer springs after them, usually across their course, and again they
all disappear together. Amidst such multitudes—for more than twenty
thousand have been judged to be out of the water together—some must fall
a prey to the enemy; but so many hunting in company, it must be long
before the pursuers abandon. From inspection we could scarcely judge the
fish to be capable of such flights, for the fins, though numerous, are
small, and the pectoral far from large, though the angle of their
articulation is well adapted to raise the fish by the direction of their
motions to the surface."
A similar species, _Cololabis saira_, with the snout very much shorter
than in the Atlantic skipper, is the _Samma_ of the fishermen of Japan.
The hard-head (_Chriodorus atherinoides_) has no beak at all and its
tricuspid incisor teeth are fitted to feed on plants. In this genus, as
in the flying-fishes, there are no finlets. The hard-head is an
excellent food-fish abundant about the Florida Keys but not yet seen
elsewhere.
[Illustration:
FIG. 166.—Saury, _Scombresox saurus_ (L.). Wood's Hole.
]
[Illustration:
FIG. 167.—Halfbeak, _Hyporhamphus unifasciatus_ (Ranzani). Chesapeake
Bay.
]
Another group between the gars and the flying-fishes is that of the
halfbeaks, or balaos, _Hemirhamphus_, etc. These are also vegetable
feeders, but with much smaller teeth, and the lower jaw with a
spear-like prolongation to which a bright-red membrane is usually
attached. Of the halfbeaks there are several genera, all of the species
swimming near the surface in schools and sometimes very swiftly. Some of
them leap into the air and sail for a short distance like flying-fishes,
with which group the halfbeaks are connected by easy gradations. The
commonest species along our Atlantic coast is _Hyporhamphus
unifasciatus_; a larger species, _Hemirhamphus brasiliensis_, abounds
about the Florida Keys. _Euleptorhamphus longirostris_, a ribbon-shaped
elongate fish, with long jaw and long pectorals, is taken in the open
sea, both in the Atlantic and Pacific, being common in Hawaii. The
Asiatic genus _Zenarchopterus_ is viviparous, having the anal fin much
modified in the male, forming an intromittent organ, as in the
_Pœciliidæ_. One species occurs in the river mouths in Samoa.
The flying-fishes have both jaws short, and at least the pectoral fins
much enlarged, so that the fish may sail in the air for a longer or
shorter distance.
[Illustration:
FIG. 168.—Sharp-nosed Flying-fish, _Fodiator acutus_ (Val.). Panama.
]
The smaller species have usually shorter fins and approach more nearly
to the halfbeaks. _Fodiator acutus_, with sharp jaws, and
_Hemiexocœtus_, with a short beak on the lower jaw, are especially
intermediate. The flight of the flying-fishes is described in detail on
p. 157, Vol. I.
The Catalina flying-fish, _Cypselurus californicus_, of the shore of
southern California is perhaps the largest of the known species,
reaching a length of 18 inches. To this genus, _Cypselurus_, having a
long dorsal and short anal, and with ventrals enlarged as well as
pectorals, belong all the species strongest in flight, _Cypselurus
heterurus_ and _furcatus_ of the Atlantic, _Cypselurus simus_ of Hawaii
and _Cypselurus agoo_ in Japan. The very young of most of these species
have a long barbel at the chin which is lost with age.
In the genus _Exonautes_ the base of anal fin is long, as long as that
of the dorsal. The species of this group, also strong in flight, are
widely distributed. Most of the European flying-fishes, as _Exonautes
rondeleti_, _Exonautes speculiger_, and _Exonautes vinciguerræ_, belong
to this group, while those of _Cypselurus_ mostly inhabit the Pacific.
The large Australian species _Exonautes unicolor_, Fig. 226, Vol. I,
belongs to this group. In the restricted genus _Exocœtus_ the ventral
fins are short and not used in flight. _Exocœtus volitans_ (_evolans_)
is a small flying-fish, with short ventral fins not used for flight. It
is perhaps the most widely distributed of all, ranging through almost
all warm seas. _Parexocœtus brachypterus_, still smaller, and with
shorter, grasshopper-like wings, is also very widely distributed. An
excellent account of the flying-fishes of the world has been given by
Dr. C. F. Lütken (1876), the University of Copenhagen, which institution
has received a remarkably fine series from trading-ships returning to
that port. Later accounts have been given by Jordan and Meek, and by
Jordan and Evermann.
[Illustration:
FIG. 169.—Catalina Flying-fish, _Cypselurus californicus_ (Cooper).
Santa Barbara.
]
Very few fossil _Exocœtidæ_ are found. Species of _Scombresox_ and
_Hemirhamphus_ are found in the Tertiary, the earliest being
_Hemirhamphus edwardsi_ from the Eocene of Monte Bolca. No fossil
flying-fishes are known, and the genera, _Exocœtus_, _Exonautes_, and
_Cypselurus_ are doubtless all of very recent origin.