LEPAS STELLATA. _Poli._ Testacea Utriusque Siciliæ (1795), Tab. 5,
fig. 18-20.
---- DEPRESSA (_var._) Ib., Tab. 5, fig. 12-16.
CHTHAMALUS STELLATUS. _Ranzani._ Memoire di Storia Naturale (1820),
Tab. 3, fig. 21-24.
---- GLABER (_var._) _Ranzani._ Ib.
---- STELLATUS. _Philippi_ (!). Enumeratio Mollusc. Siciliæ.
LEPAS PUNCTATUS. _Montagu_ (!). Testacea Britannica (1803).
_Shell white or gray, generally much corroded and punctured: radii
(when present) narrow, with their sutural edges most finely crenated;
tergum with the crests for the depressor muscle depending barely
beneath the basal margin._
_Var._ (_a_, communis) fig. 1 _a_, 1 _f_: _Shell conical depressed,
upper part corroded, walls folded, sutures moderately plain or
obliterated; radii not developed; orifice broadly oval_.
_Var. (b): Shell elongated, sub-cylindrical; sutures obliterated;
surface much corroded; orifice almost circular._
_Var._ (_c_, communis) fig. 1 _c_, 1 _e_, 1 _h_: _Shell conical,
folded, sometimes covered by membrane; radii developed, narrow;
orifice sub-hexagonal, toothed._
_Var._ (_d_, fragilis) fig. 1 _d_: _Shell conical, smooth, thin;
compartments easily separable, pale-coloured; radii developed,
narrow; orifice large, toothed, sub-hexagonal._
_Var._ (_e_, depressus) fig. 1 _b_, 1 _g_, 1 _h_: _Shell much
depressed, surface much corroded, smooth: alæ largely exposed, marked
by lines of growth: radii not present; parietes on the under side
often supported by pillars; orifice sub-hexagonal._
_Hab._--Southern shores of England, Ireland, Isle of Man,
Mediterranean, Madeira, Cape de Verde Islands, Southern United States
(Charlestown), West Indies, Brazil (Bahia), Rio Plata (Guritti
Island), Red Sea, Philippine Archipelago, Coast of China, Gulf of
Corea, Oregon or Northern California.
This species is very widely distributed and extremely common. On
the coast-rocks of the southern shores of England it is, in parts,
even more numerous than the _Balanus balanoides_, with which it
often grows mingled. As already stated, it is often confounded in
British collections with this species of Balanus, under the name
of _Balanus punctatus_; that Montagu had this Chthamalus in view,
when describing his _Lepas punctatus_, is certain, from his original
specimen in the British Museum, but whether this was the case with
his predecessor, Pulteney, in the Dorset Catalogue, I do not feel so
sure. _Chthamalus stellatus_ varies, as we shall immediately see,
extremely in appearance. Some of the varieties, as _var. depressus_,
which in external aspect are especially distinct, I have no doubt are
really varieties, but whether this is the case with some of the forms
from the more distant localities, is a little more doubtful; but I beg
that it may be observed, that I have, in the case of every one of the
varieties, and of all the specimens from distant localities, cleaned
with potash and most carefully examined the disarticulated valves, and
likewise dissected the included animal's body.
_General Appearance._--British specimens are usually conical, and
have their walls folded, corroded in their upper parts, with the
radii not developed, and the sutures more or less obliterated; in
this state the orifice of the shell is entire, and very broadly oval:
I have seen specimens in this condition from Madeira, Brazil, and the
Gulf of Corea. The shells when crowded, are rendered cylindrical,
and more or less elongated, with the sutures as viewed externally
quite obliterated; the surface rugged and much disintegrated; and
the orifice nearly circular: in this extreme condition I have seen
specimens from England, from near Genoa, and from the mouth of
the Plata: the specimens from these last two localities were of
remarkable size, being half an inch in diameter, and rather more than
half an inch in height. Again, other British specimens (fig. 1 _c_),
though not nearly so common, are rather steeply conical, and have not
only their sutures distinct, but narrow radii are plainly developed
on apparently both sides of the sutures; in this case the orifice
is slightly toothed, and is rather elongated: I have seen specimens
in this condition, but with their walls rather more deeply folded,
from the Cape de Verde and Philippine Archipelago. Other specimens,
from some unknown tropical sea, differed only in the walls being but
slightly folded, and being so perfectly preserved as to be externally
covered with membrane: this latter circumstance gave the specimens
a peculiar appearance. In this condition were some specimens (fig.
1 _d_) attached to oysters sent to me by Professor Agassiz, from
Charlestown; and which differed from all the others that I have seen,
in the thinness and smoothness of their compartments, and in the
facility with which the compartments separated from each other and
from the surface of attachment: hence I have called this form, which,
until finding more important differences, I must rank as a variety,
_fragilis_: it has stronger claims than the other varieties to be
specifically separated; but I suspect that it has been exposed to
some peculiar modifying conditions.
Lastly, we have the variety (fig. 1 _b_) excellently figured and
described by Poli, under the name of _L. depressa_: this is much
depressed, with the walls thin, not folded, with the surface much
corroded, with the sutures very distinct, with the radii not at all
or barely developed, but with the alæ largely developed, and marked
with lines of growth, resulting from the diametric growth of the
shell: the orifice is hexagonal, but broadest towards the carinal
end: most of the specimens, _but not all_, have on the under sides
of their compartments rugged pillars depending from beneath the alæ,
for the purpose, apparently, of supporting the much depressed shell.
This much depressed variety attains a larger basal diameter (but not
a greater bulk or internal capacity) than any other variety, namely,
sometimes three quarters of an inch. The great peculiarities of this
variety result, apparently, from its much depressed form, deeply
corroded not folded walls, and considerable diametric growth; from
the latter cause the alæ are largely developed; as I can find neither
internally nor externally any fixed diagnostic character I have not
hesitated to rank this form as a variety. Poli found his specimens
mingled with the ordinary _C. stellatus_, on the shores of Sicily;
and I collected at St. Jago, in the Cape de Verde Archipelago, some
specimens nearly as well characterised, also associated with the
common variety.
The shell itself is dirty-white or gray, or brown: in some varieties,
however, the white is nearly pure: internally the parietes are
generally tinted dull purple. The corium of the sack is dark
greenish-black, with a white edge to the lips lining the aperture
between the opercular valves.
_Structure of Shell and Radii, &c._--The under side of the parietes
is either quite smooth, or marked with slight, branching, depressed
lines; or mamillated; or irregularly studded with large pores. I have
already alluded to the pillars, depending from the under sides of the
alæ in most specimens of _var. depressus_: these pillars tend to form
ridges, parallel to the sides of the compartment, like those we shall
presently see in certain specimens of _C. scabrosus_. The radii are
very narrow, when best developed; their edges, when disarticulated,
can be seen, when examined by a strong lens, to be finely crenated.
The edges of the alæ are likewise very finely crenated.
_Scuta._--The outline of these valves varies considerably in
specimens taken out of the same group: we have either a nearly
equilateral triangle (fig. 1 _f_) or the tergal margin (1 _e_)
is much shorter than the other margins. There is always a deep
depression for the adductor muscle, and a small pit of very variable
depth for the lateral depressor. But the tergal margin offers
the greatest variability; here we see a very prominent articular
ridge or fold, having either a straight edge or a single or double
prominence (fig. 1 _e_-1 _h_). In specimens in the same group we
find considerable variation in these points; but the amount of
difference is sometimes so great, that I long hesitated whether
to rank some of the varieties as species. The _Terga_, likewise,
vary greatly in shape and width: in some of the commonest varieties
(and in _var. depressus_) the valve is very narrow, with the under
surface channelled or concave: in other varieties the valve is much
broader and flatter. The spur is but slightly developed. The crests
for the depressor muscles barely descend beneath the basal margin of
the valve. The articular ridge, in some varieties (as in specimens
from Madeira and the Cape de Verde Islands), is extremely prominent
and straight (1 _f_); in others, it is little prominent and deeply
sinuous (1 _h_). This great variability in the articular margins
of the scutum and tergum seems to be mainly due to the corrosion
to which these valves have been subjected, and their consequently
modified growth: in some specimens the articular ridge of the scutum,
and in others that of the tergum, has been largely developed, in
either case their mutual outlines being greatly affected.
_Branchiæ._--These are narrow, hardly at all plicated, elongated,
being about half as long as the sack. In a specimen from La Plata,
this organ ended rather more abruptly in a point than it did in other
specimens.
_Mouth._--The crest of the labrum is usually hairy, but in a specimen
from Bahia (Brazil) there were some very fine teeth. The palpi vary
somewhat in shape, and sometimes have a row of bristles along their
basal exterior margins. The mandibles usually have four main teeth,
the lowest one being confluent with the inferior pectinated angle: in
_var. depressus_, in the same individual, there were only three teeth
on one side of the mouth and five on the other; the lower main teeth
are laterally double, but generally one tooth of each pair is so
small and obscure as to be perceived with difficulty. In the maxillæ,
there are some large spines above the notch, and in the notch some
fine ones: in _var. depressus_, and in a cylindrical _var._ from La
Plata, there was quite a tuft of small spines above the notch.
_Cirri._--The outer surface of the pedicel of the second cirrus
bears a tuft of long, fine, plumose hairs: the terminal segments of
the rami of this cirrus sometimes (as in the La Plata specimens)
support a clump of coarsely pectinated spines. In specimens having
six segments in the shorter ramus of the second cirrus, the shorter
ramus of the third cirrus had fifteen segments. The two rami of the
third cirrus are usually equal in length and in the number of their
segments; but in the Brazilian specimen there were fifteen segments
in the posterior, and twenty-six in the anterior ramus; in another
specimen, fixed on a tropical Perna, there were in the two rami of
this third cirrus eighteen and twenty-four segments. In the three
posterior pairs of cirri each segment carries either four or five
pairs of main spines: the segments vary a little in the degree to
which they are elongated, being most elongated in the var. from La
Plata, with an elongated shell.
_Varieties._--It will have been observed, that the shell, in the
specimens from several distant quarters of the world over which this
species, as I believe, ranges, differs considerably in external
aspect: so do the opercular valves; and so do the parts of the
mouth and cirri: but I cannot make out that these differences are
coordinated. Thus, _var. depressus_, which is so entirely different
from the others in appearance, differs only internally in the
presence of a tuft of fine spines above the notch of the maxillæ;
and this character is found in the La Plata variety, which, as far
as the shell and opercular valves are concerned, is at the other end
of the scale of variation. Again, _var. fragilis_, from Charlestown,
presents, in the animal's body, hardly any difference. The Brazilian
specimens, which in the shell and operculum offer only quite common
characters, have the remarkable peculiarity of a considerable
difference in the length and number of the segments in the rami of
the third cirrus; they, also, have the segments of the sixth cirrus
considerably elongated, and the labrum finely toothed. Of these
peculiarities one alone, namely, the inequality in the rami of the
third cirrus, but in a lesser degree, is common to the specimens
adhering to the tropical Perna, which had a shell very unlike the
Brazilian variety, but which, on the other hand, differed scarcely in
a single character from some other specimens from an unknown tropical
sea, in which the rami of the third cirrus were quite equal. The La
Plata specimens differ most in internal characters, viz., in the
tuft of fine spines above the notch of the maxillæ, in the coarsely
pectinated spines on the tips of the second pair of cirri, in having
the segments of the sixth cirrus much elongated, and in the apex of
the branchiæ being abruptly pointed; yet in the shell and operculum
they were identical with certain Mediterranean varieties. From these
several facts, I must believe that all the widely distributed forms
here grouped together, do really belong to the same species.