LEPAS BALANOIDES. _Linn._ Fauna Succica, 1746, et Syst. Naturæ, 1767.
---- ---- _O. Fabricius._ Fauna Groen., p. 424, 1780.
---- ---- ET CLIVATUS. _Montagu_ (!). Test. Brit., 1803.
BALANUS VULGARIS (?) _Da Costa._ Hist. Nat. Testacea, Pl. 17, fig. 7,
1778.
---- OVULARIS ET ELONGATUS. _Aug. Gould_ (!). Report, Invertebrata
of Massachussetts, figs. 7 and 8, (1841).
---- PUNCTATUS, CYLINDRICUS, ELONGATUS, FISTULOSUS CLAVATUS.
_Auctorum variorum_. Sed non B. punctatus, _Bruguière_,
Encyclop. Method., et non B. punctatus, _Montagu_, Test. Brit.
_Parietes either solid, or cancellated, or rarely formed by a single
row of pores. Tergum, with the spur bluntly or sharply pointed._
_Var._ (_a_) _with the parietes permeated by tubes; spur of tergum
sharply pointed; segments in the posterior pairs of cirri, bearing
from eight to ten pairs of spines_.
_Habitat._--Great Britain, France, Norway, Shetland Islands;
Greenland, according to O. Fabricius; North America, in lat. 66°
34′ N.; Labrador; Nova Scotia; Massachussetts, Delaware. Extremely
common, attached to rocks, shells, and wood, within the tidal limits.
I have no doubt that the present species is the _Lepas balanoides_
of Linnæus; though O. Fabricius is the only author who gives, in his
"Fauna Groenlandica," a sufficient description for the species to be
recognised with certainty. I believe this also is the _B. balanoides_
of Bruguière, though he is in error, as far as my experience goes,
in stating that the basis is ever calcareous. I have little doubt,
also, that this is the _B. vulgaris_ of Da Costa. The _B. balanoides_,
in its corroded and therefore punctured state, is certainly the _B.
punctatus_ of most British collections; but I do not believe it is
the _B. punctatus_ of Montagu, which I have scarcely any doubt is
the _Chthamalus stellatus_, so often found in the southern shores of
England, and even in some of the best arranged collections, mingled
with our present species.
_General Appearance._--The shell, in middle-sized and old specimens,
is almost invariably folded longitudinally and irregularly; it is
either dirty white or very often pale brown, and punctured from the
outer lamina having been corroded, to which action it is extremely
subject. In very young specimens, the surface is usually quite white
and smooth. The shell is sometimes much depressed; generally conical,
but when crowded together, cylindrical or club-shaped, one specimen
being even more than five-and-a-half times as long as wide. In Mr.
Jeffreys' collection there is a specimen 2.5 of an inch long, .45 in
diameter at the summit, only .2 in the middle, and rather more than
.2 near the base. Another specimen was 1.8 in length, its greatest
diameter being .35 of an inch at the summit. On the other hand, I
have seen a very depressed variety, with deeply folded walls, in
Mr. Thompson's collection from near Dublin, which was no less than
four times as wide as high; so that the difference in proportion of
height and greatest width, in the two extreme specimens, was nearly
as 10 to 1. Occasionally, from some unknown cause, isolated specimens
become cylindrical. The orifice of the shell, in the much elongated
specimens, is generally deeply toothed. The radii are always narrow,
sometimes extremely narrow, and have their summits smooth and rounded.
English specimens do not usually attain half an inch in basal
diameter; I have, however, seen one from near Yarmouth .9 of an inch
in diameter. Specimens from Massachussetts seem rather larger than
the average size of British specimens, many being .6 of an inch, and
one specimen a whole inch in basal diameter.
The _opercular_ valves so closely resemble those of _B. crenatus_,
that the description is necessarily comparative; in some cases they
could hardly be discriminated; generally, owing to the disintegration
to which this species is subject, the tips of the scuta are worn off,
and hence the articular ridges together form (Pl. 7, fig. 2 _a_) a
square projection, indenting the two terga; but I have examined young
specimens and others when not disintegrated, in which the opercular
valves, viewed externally, presented no difference whatever from
those of _B. crenatus_. The _scuta_, however, are, I think, generally
rather thicker, with the growth-ridges more prominent, and with
the tips certainly less reflexed than is usual with _B. crenatus_.
Internally, the articular ridge is rather less prominent: there is
no distinct adductor ridge. The _terga_ are often rather narrower
in proportion, and this especially holds good in the elongated
varieties; in these latter, there is occasionally a moderately deep
longitudinal furrow: the spur is often exactly the same shape as in
_B. crenatus_, but it is apt to be rather longer (Pl. 7, fig. 2 _c_)
and more pointed: in _var._ (_a_) it is pointed (fig. 2 _d_) in a
very remarkable manner. Internally, the articular ridge is decidedly
more prominent than in _B. crenatus_; the crests for the tergal
depressor muscles are either well developed or almost absent. From
this description it will be seen, how singularly the opercular valves
of the common varieties of these two species resemble each other. I
may mention that in some of the much elongated specimens, the muscles
going to the opercular valves partially lose their transverse striæ,
and become ligamentous.
The _Parietes_ are either quite solid, or more commonly are permeated
by minute pores, or by small irregular square tubes (Pl. 7, fig. 2
_b_), which only run up each successive zone of growth, for very
short distances, giving to the shell a cancellated structure, which
from corrosion is often externally visible. In the rather rare
variety (_a_) the parietes are permeated by regular tubes, extending
up to the apices of the compartments, but crossed by transverse
septa. The longitudinal septa, when such can be said to occur, in
no case are denticulated at their bases. The internal surface of
the parietes is either quite smooth or is traversed (Pl. 7, fig. 2
_b_) by very slight anastomosing ridges, but never, even in _var._
(_a_), by regular longitudinal ribs, as in most other species. The
carinal margin of each compartment, on the inside, projects, as in
_B. crenatus_, inwards, beyond the general surface of the shell, and
running down, rests on the basal membrane. The lower edge of the
sheath is rarely hollow beneath. The walls are lined by purplish,
or pale brown, or sometimes by almost black corium; numerous tubuli
penetrate the under sides of the walls and opercular valves; and
it is the intersection of these tubuli that gives the punctured
appearance to the often corroded surface of the shell. The _radii_
are narrow, generally very narrow; they have their upper and outer
margins, as seen externally, very oblique, rounded and (when well
preserved) smooth; their sutural edges are either quite smooth,
or sometimes just perceptibly pitted, like the basal margin of
the walls, or occasionally furnished with globular or arborescent
little ridges. The _alæ_ are also very oblique, but to a variable
degree, sometimes only slightly oblique: their sutural edges are
either smooth or obscurely crenated. _Basis_, membranous; in some
much elongated specimens, during continued growth, the basal edges
of the compartments approach each other so closely as almost to
touch, so that the whole shell becomes pointed at the bottom; but
on careful inspection I have never failed to find, even in the most
pointed specimens, a minute basal membrane; in other much elongated
varieties, in which the shell has apparently become too large for the
animal's body, the basal membrane, instead of being flat, becomes
drawn up deeply inwards, so as to touch the surface of attachment
only close round the basal edges of the shell.
_Mouth_: labrum with the teeth on each side of the central notch
unusually variable in number; I have seen specimens with only two
on each side, with four on each side, with five on one side and
four on the other, with five on one side and none on the other,
and with six on both sides; hence the total number ranges from four
to twelve. Mandibles, with the fourth and fifth teeth small, or
quite rudimentary. Maxillæ, with scarcely even a trace of a notch
under the upper pair of spines. _Cirri_; first pair, with one ramus
one third or one fourth longer than the other; in one specimen the
number of segments were nine and sixteen in the two rami: second
and third cirri short, very nearly equal in length, having in the
just-mentioned specimen respectively ten and eleven segments; the
sixth cirrus in this same specimen had twenty-five segments, each
segment being about as long as broad, and supporting six pairs of
spines. In the singular variety (_a_) the posterior cirri are more
elongated, and each segment supports seven or eight, and in one case
even ten pairs of spines! the third pair is also in this variety
proportionally rather longer. At the base of the third pair there
is a tuft of fine spines. The penis has not, as in _B. crenatus_, a
point at its dorsal basis. The branchiæ are very little plicated.
_Varieties._
Of the varieties having much elongated, club-shaped, hour-glass
shaped, and depressed shells, there is no necessity to say anything
in particular. With respect to the remarkable variety (_a_), I at
first named and described it as a distinct species: I have received
two lots, both from North America, one being sent me by Professor
Agassiz from Cape Cod. These agreed in having the parietes permeated
by regular tubes; in having the spur of the tergum most sharply
pointed; in the third pair of cirri being proportionally longer
compared with the second pair; in the sixth pair having more numerous
segments, namely, three times as many as in the third pair; in the
segments of the posterior cirri being more elongated, and especially
in the number of pairs of spines on each segment--amounting in one
case even to ten, a number unparalleled in other cirripedes. It may
naturally be asked why I have not retained so well marked a form as
a distinct species? In the first place, I found the most remarkable
character in _var._ (_a_), namely, the number of pairs of spines
on the posterior cirri variable, there being in one lot seven or
eight pairs, and in the other lot nine or ten pairs on each segment.
Secondly, all the characters by which this variety differs from the
common _B. balanoides_, are those which are variable in the latter;
this is especially the case with the structure of the parietes, and
in a lesser degree with the spur of the tergum. Thirdly, I found a
specimen in Mr. Cuming's collection, from Sweden (so that this _var._
(_a_) is not confined to North America), in which the cirri quite
resembled those of the American specimens, but the spur of the tergum
was in an intermediate condition as compared to that of ordinary
varieties; and the parietal tubes were of unequal sizes, and scarcely
more regular than sometimes in the true _B. balanoides_. And lastly,
I have seen specimens from Ayrshire, with the parietes permeated by
regular tubes, but with the tergum in an intermediate condition, and
with the segments of the posterior cirri not more numerous or more
elongated than in _B. balanoides_, supporting only six or seven pairs
of spines, that is only one more than is common with _B. balanoides_;
so that it was impossible to decide whether to rank the Ayrshire
specimen under _var._ (_a_) or under the common form, so that I was
compelled to give up _var._ (_a_) as a species.
_Monstrous individuals, with the male organs aborted:
Parasite._--Amongst some specimens, chiefly elongated ones, sent to
me from Tenby, in South Wales, I found no less than seven individuals
with some of the posterior cirri distorted, unequal on the opposite
sides, and in an almost rudimentary condition, and in each case
with the penis truncated, without any muscle entering the stump,
which was _absolutely imperforate_: the vesiculæ seminales were
much shrunk; in one case without any zoosperms; in another case
with headless zoosperms cohering in an unusual manner; hence it is
certain that these individuals were functionally only female, and
could not impregnate their own ova; yet in two instances the ova
had been impregnated, no doubt by neighbouring perfect individuals,
for they contained well-developed larvæ. Several of these monstrous
individuals were infested by one, two, or three curious crustaceans,
which have been described by Mr. Goodsir,[97] as the male of the
Balanus; but these supposed males are females, and were distended
with ova containing almost mature larvæ; I believe that they are the
females of the unnamed genus, belonging to the family of Ioniens,
described by Mr. Goodsir, which live parasitic within the sack (as I
likewise found) of the same individual Balani.
[97] 'Edinburgh New Philosophical Journal,' July, 1843.
_Diagnosis._--I have seen several specimens of this species and of
_B. crenatus_, absolutely undistinguishable in external appearance. I
may specify one of _B. balanoides_, imbedded in an alcyonidium, and
one of _B. crenatus_, imbedded in a sponge, and therefore neither at
all abraded. Generally, the tips of the scuta in _B. crenatus_ are a
little reflexed, whereas in _B. balanoides_, when the shell has been
at all disintegrated, the tips form a square projection locked into
the terga. _Bal. crenatus_ never assumes the punctured appearance so
common in _B. balanoides_. Very young specimens of the latter can be
distinguished by their dead white colour and smoothness. The edges
of the radii are almost always smoother than in _B. crenatus_, and
they are never so wide as is sometimes the case with _B. crenatus_.
When a specimen is disarticulated, our present species can at once
be distinguished from _B. crenatus_ (and from _B. improvisus_), by
its membranous basis, and by the solid or cancellated walls, which
are rarely permeated by regular tubes or pores; and the walls when
porose are not internally ribbed. I have already pointed out the
few very trifling points, in which the opercula of the two species
differ. The mouth and cirri offer likewise very few differences: in
_B. balanoides_ there are often more teeth on the labrum than in _B.
crenatus_; the rami of the first cirri are perhaps here rather less
unequal; the second and third pairs of cirri are certainly in most
cases more equal in length; and lastly, the segments of the sixth
cirri, even in the common varieties, bear, in equal-sized specimens,
more pairs of spines than in _B. crenatus_. We shall see that in
habits, with regard to depth, the two species differ, _B. balanoides_
inhabiting much shallower water than _B. crenatus_.
_Range, Habitats, &c._--This species is extraordinarily abundant
within the tidal limits round the shores of Great Britain, and
apparently of the northern United States. Besides numerous specimens
sent to me from very many English localities, the late Mr. W.
Thompson, of Belfast, kindly placed in my hands his very large
collection; from these materials it appears that _B. balanoides_
is the only tidal species in the northern parts of our island; but
in the south and south-west, it is associated with the _Chthamalus
stellatus_ and _Balanus perforatus_. I doubt whether this species
ever lives below the lowest tides; the case of a few specimens being
mingled with _B. improvisus_ and _crenatus_, (mentioned under the
latter species,) at the bottom of a rudder of a small vessel, about
six feet deep, is hardly an exception, for the water would there
be troubled and aërated almost as in a breaker; and on this very
rudder the upper two or three feet were coated exclusively by the
_B. balanoides_. This species lives on rocks at both the uppermost
and lowest limit of the tides; I am informed by Mr. Thompson, that
he has seen specimens attached to a spot not covered by water
during neap-tides. As a proof of its tenacity of life, Mr. Thompson
informs me that he accidentally kept some specimens in a box, in a
warm sitting-room, and found them alive seven days afterwards. This
same most accurate observer finds, however, that _B. balanoides_
is very susceptible to brackish water; he says, "that having kept
some specimens alive for a week in excellent health, the water being
changed once in thirty-six hours, they were one day killed instantly
by some water, though brought from the same part of the estuary as
usual, having been rendered brackish by much rain having lately
fallen." I may recall the fact, that _B. improvisus_ lives daily for
hours in absolutely fresh running water.
The _B. balanoides_ lives attached, often continuously coating
many square feet of the surface, to rocks, pebbles, wooden-piers,
littoral shells and ulvæ. The most northern point whence I have
received specimens, is in lat. 66° 34′ in North America, collected
by Mr. Sutherland; and the most southern point is Delaware Bay, in
the United States, in lat. 39°; I do not believe that this species
extends into the Mediterranean, for Ranzani (Mem. di Storia Nat.),
who particularly attended to the nature of the basis, was not
acquainted with any _Balanus_ having a membranous basis; and Poli
(Test. Ut. Siciliæ,) describes only two species thus characterised,
and these are manifestly _Chthamali_.
With respect to the rate of growth of this species, I am indebted to
Mr. W. Thompson for the following note:--
"Sept. 29, 1848.--I examined a great number of Balani, in reference
to the growth made by them during the present season, and found it
to average three lines in diameter, and at most four lines. I saw a
few minute specimens, only one line in diameter, showing that the
species continued to breed until lately: these latter were probably
not more than four weeks old. The young of the present year are
plainly distinguished from the older ones, by their pure white colour
and fresh appearance. Judging from the size of this year's specimens,
and of the older ones on the same stones, I am of opinion that the
term of life of the species is two years. Of the older shells, which
I examined and found living in the spring, nine tenths are now dead,
the walls only remaining, the opercular valves having been washed
away."
Mr. Thompson goes on to say, that the individuals which had, on July 3,
a basal diameter of from two and a half to three lines, had attained,
by the 30th of September, a diameter of four and a half lines, this
being here the maximum size of the species.