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James G. (James George) Needham.

The life of inland waters; an elementary text book of fresh-water biology for students online

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to the sides of the body, as befits slipping in and out
of their cases. The front third of the body is strongly
chitinized and often brightly pigmented; the
remainder, that is constantly covered by the case, is
thin skinned and pale. Most caddis-worms bear fila-
mentous gills along the sides of the abdomen, but some
that dwell in streams are gill-less and others have gills
in great compound clusters or tufts.




FIG. 125. The larva of Rhyacophila
fuscula in its barricade of stones,
exposed by lifting off a large top
stone.



21 8 Aquatic Organisms

Caddis -fly pupae are likewise aquatic (and this is
characteristic of no other order of insects) , and like the
larvae, they often bear filamentous gills along the sides
of the abdomen. They are equipped with huge mandi-
bles that are supposed to be of use in cutting a way out
through the silk just before transformation. The
mandibles are shed at this time. The adult caddis-flies
are destitute of jaws and are not known to feed; so
they are probably short-lived.




FIG. 126. Eggs of Triaenodes.

The eggs of caddis-flies usually are laid in clumps of
gelatine. Sometimes they are arranged in a flat spiral,
as in Triaenodes, shown in the accompanying figure:
sometimes they are suspended from twigs in a ring-like
loop, as in Phryganea. Oftener they form an irregular
clump. They are usually of a bright greenish color,
but those of the net spinning Hydropsyches, laid on
submerged stones in close patches with little gelatine,
are tinged with a brick-red color.

The moths (order Lepidoptera) are nearly all terres-
trial. Out of this great order of insects only a few
members of one small family (Pyralidae) have entered
the water to live. These live as larvae for the most part
upon plants like water lilies and pond weeds that are
not wholly submerged. Hydrocampa, removed from



Moths



219



its case of two leaf fragments, looks like any related land
caterpillar, with its small brown head, its strongly




FIG. 127. Two larval cases of the moth
Hydrocampa, each made of two pieces
of Marsilea leaf. Upper smaller case
unopened, larva inside; lower case opened
to show the larva, its cover below.

chitinized prothorax and the series of fleshy prolegs
underneath the abdomen. By these same characters
any other aquatic caterpillar may be distinguished from
the members of other orders. Paraponyx makes no



220



Aquatic Organisms



case, differs strikingly in being covered with an
abundance of forking filamentous gills which sur-
round the body as with a whitish fringe. It feeds, often
in some numbers, on the under side of leaves of the white
water-lily, or about the sheathing leaf bases of the
broad-leaved pond weeds (Potamogeton).

Elophila fulicalis lives on the exposed surfaces of
stones in running streams, dwelling under a silt-covered
canopy of thin-spun silk, about the edges of which it
forages for algse growing on the stones. Its body is




FIG. 128. Larva of Elophila

depressed, and its gills are unbranched and in a
double row along each side. It spins a dome-shaped
cover having perforate margins under which to pass
the pupal period. It emerges, to fly in companies of
dainty little moths by the streamside.

All these aquatic caterpillars like their relatives on
land, are herbivorous. They are all small species;
they are of wide distribution and are often locally
abundant.

The beetles (order Coleoptera) are mainly terrestrial,
there being but half a dozen of the eighty-odd families
of our fauna that are commonly found in the water.
Both adults and larvae are aquatic, but, unlike the bugs,
the beetles undergo extensive metamorphosis, and



Beetles



221



larvae and adults are of very different appearance.
Beetle larvae most resemble certain neuropteroids of the
family Sialididae in appearance, and there is no single
character that will distinguish all of them (see fig. 121 on
p. 214). Only a few beetle larvae (Gyrinids, and a few
Hydrophilids like Berosus) possess paired lateral fila-
ments on the sides of the abdomen such as are charac-
teristic of all the Sialididae.
Aquatic beetle larvae are
much like the larvae of the
ground beetles (Carabidae)
in general appearance, hav-
ing well developed legs and
antennae and stout rapacious
jaws.

Best known of water
beetles are doubtless the
' 'whirl - i - gigs" (Gyrinidae) ,
which being social in their
habits and given to gyrating
in conspicuous companies on
the surface of still waters,
could hardly escape the
notice of the most casual ob-
server. Their larvae, how-
ever, are less familiar. They

are pale whitish or yellowish translucent elongate crea-
tures, with very long and slender paired lateral ab-
dominal filaments along the sides of the abdomen.
They live amid the bottom trash where they feed upon
the body fluids of blood worms and other small
animal prey. Living often in broad expanses of shoal
water where there are no banks upon which to crawl
out for pupation, they construct a blackish cocoon
on the side of some vertical stem just above the surface
of the water and undergo transformation there. The




FlG. 129. A diving beetle,
Dytiscus, slightly enlarged.



222



Aquatic Organisms




eggs are often laid on the under side of floating leaves

of pond weeds.

The diving beetles (Dytiscidae and
Hydrophilidae) are by far the most num-
erous and important of the aquatic
beetles. These swarm in every pond
and pool, and are among the most
important carnivores of all such waters.
They range in size from the big brown
Dytiscus (fig. 129) down to little fellows
a millimeter long. Their prevailing
colors are brown or black, but many of

FIG. 130. One of the lesser forms are prettily flecked and

the lesser diving
beetles, Hydro-
porus, seven
times natural



streaked with
yellow (fig. 130).
The eggs of the
Dytiscus and of
other members
of its family are
inserted singly
into punctures in
the tissues of
living plants (fig.
131). Those of
the Hydrophilids
are for the most
part inclosed in
whitish silken
cocoons attached
to plants near the
surface of the
water.




FIG. 131. Eggs of the diving beetle,
Dytiscus, in submerged leafstalks, nearly
ready for hatching: the larva shows
through the shell. (From Matheson)



Beetles



22$



The Haliplids are a small family of minute beetles,
having larvae of unique form and habits. These larvae




FIG. 132. Larvae of the beetle, Peltodytes,
in mixed algal filaments, twice natural
size; below, a single larva more highly
magnified. (From Matheson).

live among the tangled filaments of the coarser green
algae, especially Spirogyra, and they feed upon the
contents of the cells that compose the filaments, sucking



224 Aquatic Organisms

the contents of the cells, one by one. They are very
inert-looking, stick-like, creatures and easily pass
unobserved. Of our two common genera one (Pelto-
dytes) is shown in figure 132. The body is covered
over with very long stiff jointed bristle-like processes,
giving it a burr-like appearance. The larva of the
other genus (Haliplus) is more stick-like, has merely
sharp tubercles upon the back, and has the body ter-
minating in a long slender tail.

The Riffle beetles (Parnidae and Amphizoid^e) prefer
flowing water. They do not swim, but clamber over
the surfaces of logs and stones. They are mostly small
beetles of sprawling form, having stout legs that
terminate in curved grappling claws. There is great
variety of form among their larvae, the better adapted
ones that live in swift waters showing a marked ten-
dency to assume a limpet-like contour. This cul-
minates in the larva of Psephenus, commonly known as
the " water penny." This larva was mistaken for a
limpet by its original describer. It is very much
flattened and broadened and nearly circular in outline,
and the flaring lateral margins encircling and inclosing
the body fit down all round to the surface of the stone
on which it rests (see fig. 160 on page 260). Under-
neath its body are tufts of fine filamentous gills, inter-
segmentally arranged.

The flies (order Diptera) are a vast group of insects.
Among them are many families whose larvae are wholly
or in part aquatic. The changes of form undergone
during metamorphosis are at a maximum in this group :
the larvae are very different indeed from the adults.

Dipterous larvae are very diversified in form and
details of structure. The entire lack of thoracic legs
will distinguish them from all other aquatic larvae.
They agree in little else than this, and the general



Flies



225



tendency toward the reduction of the size of the head
and of the appendages. Many of them are gill -less and
many more possess but a single cluster of four tapering
retractile anal gill filaments.




FIG. 133. An adult midge, T any pus carneus,
male.



By far the most important of the aquatic Diptera in
the economy of nature are the midges (Chironomidae) .
These abound in all fresh waters. The larvae are
cylindric and elongate, with distinct free head, and body
mostly hairless save for caudal tufts of setae. They are
distinguished from other fly larvae by the possession of a
double fleshy proleg underneath the prothorax, and a
pair of prolegs at the rear end of the body, all armed
with numerous minute grappling hooks. Many of
them are of a bright red color, and are hence called
"blood worms."



226



Aquatic Organisms



Midge larvae live mainly in tubes which they fashion
out of bits of sediment held together by means of the
secretion of their own silk glands. These tubes are
built up out of the mud in the pond bottom as shown in
the accompanying figure, or constructed in the crevices




FIG. 134. Tubes of midge larvae in the bed of a pool.

between leaves, or attached to stems or stones or any
solid support. They are never portable cases. They
are generally rather soft and flocculent. The pupal
stage is usually passed within the same tubes and the
pupa is equipped with respiratory horns or tufts of
various sorts for getting its air supply. The pupa (see
fig. 171 on p. 279) is active and its body is constantly
undulating, as in the caddisflies.

The eggs of the midges are laid in gelatinous strings
in clumps and are usually deposited at the surface of
the water. Figure 135 shows the appearance of a bit
of such an egg-mass. This one measured bushels in



Flies



227



quantity, and doubtless was laid by thousands of
midges. Figure 136 shows a little bit of it a portion
of a few egg strings magnified so as to show the form
and arrangement of the individual eggs. Such great
egg masses are not uncommon, and they foreshadow the
coming of larvae in the water in almost unbelievable
abundance.




FIG. 135. A little hit of an egg mass of the midge,
Chironomus, hung on water weeds (Philotria).

Midge larvae are among the greatest producers of
animal food. They are preyed upon extensively, and
by all sorts of aquatic carnivores.

Three families of blood-sucking Diptera have aquatic
larvae; the mosquitoes (Culicidae), the horseflies
(Tabanidae) and the black flies (Simuliidae) . Mosquito



228 Aquatic Organisms

larvae are the well known "wrigglers" that live in rain
water barrels and in temporary pools. They are
readily distinguished from other Dipterous larvae by
their swollen thoracic segments and their tail fin. The
pupae are free swimming and hang suspended at the
surface with a pair of large respiratory horns or trum-
pets in contact with the surface when at rest.




FIG. 136. A few of the component egg-strings, magnified.

The larvae of the horseflies are burrowers in the mud
of the bottom. They are cylindric in form, tapering
to both ends, headless, appendageless, hairless, and
have the translucent and very mobile body ringed with
segment ally arranged tubercles. They are carnivorous,
and feed upon the body fluids of snails and aquatic
worms and other animals. The white spiny pupae are



Flies 229

formed in the mud of the shore. The tiny black eggs
(fig. 138) are laid in close patches on the vertical stems
or leaves of emergent aquatic plants.

Black fly larvae live in rapid streams, attached in
companies to the surfaces of rocks or timbers over
which the swiftest water pours. They are blackish,
and often conspicuous at a distance by reason of their
numbers. They have cylindric bodies that are swollen
toward the posterior end, which is attached to the
supporting sxirface by a sucking disc. Underneath the
mouth is a single median proleg, and on the front of the
head convenient to the mouth, there is a pair of "fans,"
whose function is to strain forage organisms out of the
passing current. The full grown larva spins a basket-
like cocoon on the vertical face of the rock or timber,
and in this passes its pupal stage. The eggs are laid
in irregular masses at the edge of the current where the
water runs swiftest.

In like situations we meet less frequently the net-
winged midges (Blepharoceridae) , whose scalloped flat
and somewhat limpet -shaped larvae are at once recogniz-
able by the possession of a midventral row of suckers
for holding on to the rock in the bed of the rushing
waters. The naked pupa is found in the same situation
and is attached by one strongly flattened side to the
supporting surface.

These five above-mentioned families are the ones
most given over to aquatic habits. Then there are
several large families a few of whose members are
aquatic: Leptidae, whose larvae live among the rocks
in rapid streams, hanging on and creeping by means of
a series of large paired and bifid prolegs; Syrphidae,
whose larvae are known as "rat-tailed maggots'* since
their body ends in a long flexuous respiratory tube,
which is projected to the surface for air when the larva
lives in dirty pools ; Craneflies (Tipulidae) see fig. 2 1 5 on



230



Aquatic Organisms




FIG. 137. The larva of a horsefly, Chrysops.




FIG. 138. The eggs
of a horsefly on
an emergent bur-
reed leaf.



p. 360) whose cylindric tough-
skinned larvae have their heads
retracted within the prothorax,
and bear on the end of the abdo-
men a respiratory disc perforate
by two big spiracles and sur-
rounded by fleshy radiating fila-
ments; minute moth-flies Psycho-
didae, (see fig. 214 on p. 359)
whose slender larvae live amid
the trash in both brooks and
swales. Swaleflies (Sciomyzidae)
whose headless and appendage-
less larvae hang suspended by
their posterior end from the sur-
face in still water; and others
less common.

It is a vast array of forms this
order comprises, this mighty group
of two-winged flies, that is still so
imperfectly known; and some of
the most highly diversified of its
larvae are among the commoner
aquatic ones.



VERTEBRATES

There is little need that we should give any extended
account of the groups of back-boned animals fishes,
amphibians, reptiles, birds and mammals. In water as
on land they are the largest of animals, and are all
familiar. The water- dwellers among them, excepting
the fishes and a very few others, are air-breath-
ing forms that are mainly descended from a terrestrial
ancestry. They haunt the water-side and enter the
shoals to forage or to escape enemies, but they cannot
remain submerged, for they have need of air to breathe.

The fishes have remained strictly aquatic. They
dominate the open waters of the larger lakes and streams.
They have multiplied and differentiated and become
adapted to every sort of situation where there is water
of depth and permanence sufficient for their mainten-
ance. They outnumber in species every other verte-
brate group.

Within the water the worst enemies of fishes are
other fishes; for the group is mainly carnivorous, and
big fishes are given to eating little ones. Hence, tho
all can swim, few of them do swim in the open waters,
and these only when well grown. Those that so expose
themselves must be fleet enough to escape enemies, or
powerful enough to fight them. Little fishes and the
greater number of mature fishes keep more or less
closely to the shelter of shores and vegetation. The
accompanying diagram, based on Hankinson's (08)
studies at Walnut Lake, Michigan, represents the
distribution of fishes in a rather simple case. The
thirty-one species here present range in adult size
from the pike which attains a length above three feet,
to the least darter which reaches a length of scarcely an
inch and a half. One species only, the whitefish,

231



232



Aquatic Organisms



dwells habitually in the deep waters of the lake. One
other species, the common sucker, is a regular inhabit-
ant of water between fifteen and forty feet in depth.
The pike, ranges the upper waters at will pursuing his
prey over both depths and shoals; but he appears to
prefer to lie at rest among the water-weeds where his




FIG. 139. Ale-wives (Clupea pseudoharengus) on the beach of Cayuga Lake,
after the close of the spawning season. A single large sucker lies in the
foreground.

great mottled back becomes invisible among the lights
and shadows.

The pondweed zone on the sloping bottom between
five and twenty-five feet in depth is the haunt of most
of the remaining species, including all the minnows, cat-
fishes, sunfishes, and the perches. The last named
wander betimes more freely into the deep water; all of



Distribution of Fishes



'33



these forage in the shoals, especially at night. The
catfishes are more strictly bottom feeders, and these
feed mainly at night. A few species keep to the close
shelter of thick vegetation at the water's edge, and one
species, the least darter, prefers to lie over mottled
marl-strewn bottoms at depth between fifteen and
twenty feet.

So it appears that some two-thirds of the species
have their center of abundance in the pondweed zone :
here, Doubtless they best find food and escape enemies.



TT

20
40
60

80
100



con
O.



^,, 'pondweed zone

a, whitefish, i species.

c, pike, i species.

e, sucker, i species.

n, perch and wall-eye, 2 species.

o, bass, sunfish, minnow, etc.,

19 species.

r, catfishes, 2 species.
s, mudminnow, etc., 3 species.
x, least darter, i species.

FIG. 140. Diagram illustrating the habit-
ual distribution of the thirty-one species
of fishes in Walnut Lake, Michigan.
Data from Hankinson.



Only a few of the stronger and swifter species venture
much into the deeper water: the weaklings and the
little fishes frequent the weed-covered shoals.

The eggs of fishes are cared for in a great variety of
ways. Their number is proportionate to the amount of
nurture they receive. No species scatters its eggs
throughout the whole of its range, but each species
selects a spot more or less circumscribed in which to lay
its young. Carp enter the shoals and scatter their eggs
promiscuously over the submerged vegetation and the
bottom mud with much tumult and splashing. A
single female may lay upwards of 400,000 eggs a season.



234 Aquatic Organisms

Doubtless many of these eggs are smothered in mud and
many others are eaten before hatching. Suckers seek
out gravelly shoals, preferably in the beds of streams, at
spawning time. Dangers are fewer here and a single
female may lay 50,000 eggs. Yellow perch attach their
eggs in strings of gelatin trailed over the surface of
submerged water plants. The number per fish is still




FIG. 141. A splash on the surface made by a carp in spawning.

further reduced to some 20,000 eggs. Sunfishes make
a sort of nest. They excavate for it by brushing away
the mud with a sweeping movement of the pectoral fins.
Thus they uncover the roots of aquatic plants over a
circular area having a diameter equal to the length of
the fish. On these roots the female lays her eggs, and
the male guards them until they are hatched. With
this additional care the number is further reduced to
some 5000 eggs. Sticklebacks actually build a nest, by



Food of Fishes 235



gathering and fastening together bits of vegetation.
It is built in the tops of the weeds not on the pond
bottom. The nest is roughly spherical, with a hole
through the middle of it from side to side. Within the
dilated center of the passageway the female lays her
eggs: the male stands guard over the nest. After the
hatching of the eggs he still guards the young. It is
said that when the young too early leave the nest, he
catches them in his mouth and puts them back. The
stickleback lays only about 250 eggs.

Thus in their extraordinary range of fecundity the
fishes illustrate the wonderful balance in nature. For
every species the number of young is sufficient to
meet the losses to which the species is exposed.

The food of fresh-water fishes covers a very wide
range of organic products ; but the group as a whole is
predaceous. A few, like the goldfishes and golden
shiners, are mainly herbivorous and live on algae and
other soft plant stuffs. Others like carp and gizzard-
shad live mainly on the organic stuffs they get by
devouring the bottom ooze. Many, either from choice
or from necessity, have a mixed diet of plant and animal
foods. But the carnivorous habit is most widespread
among them. In inland waters they are the greatest
consumers of animal foods.

Such fishes as the pike which, when grown, lives
wholly upon a diet of other fishes, are equipped with an
abundance of sharp raptorial teeth. The sheepshead
has flattened molar-like teeth strong enough for crushing
shells and adapting it to a diet of molluscs. Other
fishes, even large ones like the shovel-nosed sturgeon,
have close-set gill-rakers. These retain for food
the plancton organisms of the water that is strained
through the gills. The young of all fishes are plancton
feeders.



236



Aquatic Organisms



The Amphibians are the smallest of the five great
groups of vertebrates. They are represented in our
fauna mainly by frogs and salamanders. A few of the
more primitive salamanders (Urodela) , such asNecturus,
breathe throughout life by means of gills, and are
strictly aquatic. A few are terrestrial, but most are
truly amphibious. They develop as aquatic larvae
(tadpoles), having gills for breathing and a fish-like
circulation: they transform to air-breathing, more or
less terrestrial adult forms; and they return to the
water to lay their eggs in the primeval environment.




FIG. 142. A leopard frog. Rana pipiens.

The period of larval life varies from less than two
months in the toad to more than two years in the bull-
frog.

The eggs of amphibians are, for the most part, de-
posited in shallow water, often in masses in copious
gelatinous envelopes (see fig. 201 on p. 342). In some
cases the egg masses are large and conspicuous and well
known. Examples are the long egg-strings of the toad
that lie trailing across the weeds and the bottom; or
the half -floating masses of innumerable eggs laid by the
larger frogs. The eggs of the smaller frogs are less
often seen, those of the peeper being attached singly
to plant stems. Dr. A. H. Wright (14) has shown that
the eggs of all our species of frogs are distinguishable
by size, color, gelatinous envelopes and character of
cluster.



Amphibians



237




Adult amphibians are carnivorous. They all eat
lesser animals in great variety. Frogs and toads have
a projectile and adhesive tongue which is of great service
in capturing flying insects; but they eat, also, many
other less active morsels of flesh that they find on the
ground or in the water.
The food of some of the
lesser stream-inhabiting
salamanders , such as
Spelerpes, is mainly in-
sects, while that of the
vermilion-spotted newt
is mainly molluscs.

The amphibia are a
group of very great bio-
logical interest. They
represent a relatively
simple type of vertebrate
structure. Their devel-
opment can be followed
with ease and it is illumi-
nating and suggestive of
the early evolutionary history of the higher verte-
brates. They illustrate in their own free-living forms
the transition from aquatic to terrestrial life. And they
show in the different amphibian types many grades of
metamorphosis. The transformation is more extensive



FIG. 143. Diagram of individual eggs
from the egg mass of the toad and
seven species of frog occurring at
Ithaca. Eggs solid black; gelati-
nous envelopes white. (After
Wright).

A, Toad, eggs in double gelatinous tubes, form-
ing strings, the inner tube divided by cross
partitions; B, pickerel frog; C, peeper (no
outer envelope) ; D, green frog (inner en-
velope ellipitical) ; E, tree frog (outer en-
velope ragged); F, bull frog (no inner
envelope); G, leopard frog; H, wood frog.


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Online LibraryJames G. (James George) NeedhamThe life of inland waters; an elementary text book of fresh-water biology for students → online text (page 13 of 26)