A Monograph on the Sub-class Cirripedia · Charles Darwin
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There can be no doubt that this species is the _B. nigrescens_ in Chenu, who had access to Lamarck's original specimens; and there can be equally little doubt that it is the _B. gigas_ of Ranzani, collected, during Baudin's expedition, at King George's Sound: it is essentially allied to _B. psittacus_, but in external appearance strikingly resembles some of the varieties of _B. tintinnabulum_. _General Appearance._--Shape tubulo-conical: walls smooth, sometimes longitudinally ribbed: colour ashy-gray tinged with blue, but many specimens are dark purplish-blue, owing to the disintegration of the outer lamina, and consequent exposure of the almost solidly filled up, dark blueish parietal tubes; on the other hand, some specimens are quite white. Ranzani describes the colour as earthy-violet, which is very characteristic of some of the specimens. The orifice is apt to be rather small, compared to the size of the specimens, and tends to be hexagonal. The radii are often rather narrow. The opercular valves are tinted pale blue. The basal diameter of the largest specimen is two inches, and its height two and a quarter. The _Scuta_ have their basi-tergal corner much rounded off, as in _B. psittacus_, so that the tergal margin does not extend more than half down the valve. The surface is somewhat prominent, along a line running from the apex to the point of chief curvature in the basal margin. The surface is not striated. Internally, the articular ridge is little prominent, and not reflexed; the lower end depends as a free, sharp style or point. The adductor ridge is moderately sharp, and stands some little way distant from the articular ridge: it is produced downwards, and forms a moderately deep and large cavity for the depressor muscle; but this cavity is not closed, and does not extend up, as in the two last species, to the apex of the valve.
_Terga_, narrow, with a sharp, prominent, needle-like beak. Spur, long, narrow, placed at less than its own width from the basi-scutal angle: the basal margin on both sides slopes down to the spur: the scutal margin is not inflected. Internally, the articular ridge is very feebly developed, but extends down close to the basi-scutal angle. On the under surface in the upper part of the valve, there is a short, very slight ridge, extending on the carinal side, near and parallel to the articular ridge; this slight ridge plays an important part, as in the two foregoing species, in the formation of the beak or apex. Crests for the depressor muscle are hardly distinguishable. The _Walls_ appear to vary in some degree in strength and thickness; as is likewise the case with the opercular valves. In some of the thinner specimens, the parietal tubes are large, and the longitudinal septa are furnished with small, sharp denticula. The tubes are often thickly lined or almost filled up solidly with blue shell; they are not crossed by transverse septa. The _Radii_ vary in width; externally they are often finely ribbed transversely, at other times they are smooth; their septa are fine and thin, with their delicate denticuli not extending to the outer lamina: they are very porose. The _alæ_ have their summits parallel to the basis; their sutural edges are most finely crenated. The sheath is blueish, excepting the wedge-like portions of the alæ which have been added during the diametric growth, and these are white.
_Mouth_: labrum without teeth: mandibles with five sharp teeth: maxillæ with the edge straight. _Cirri_, first pair with the rami very slightly unequal; segments of the shorter ramus and of both rami of the second pair protuberant: posterior cirri with the segments shield-shaped in front, bearing four pairs of spines, of which the upper pair is much longer than the lower pairs; each pair has a small intermediate tuft of minute spines. 6. BALANUS DECORUS. Pl. 2, fig. 6 _a_, 6 _b_. _Parietes pale pink; radii rather darker. Scutum with a small articular ridge. Tergum with the longitudinal furrow very shallow and open; basal margin on both sides sloping towards the spur._ _Hab._--New Zealand. Mus. Brit., and Flower: attached to shells. _General Appearance._--Shell conical or tubular, with a large rhomboidal orifice; very pale pink, but tinted yellowish from the persistent epidermis, and sometimes faintly striped longitudinally; radii and sheath of rather a darker pink; scuta in themselves white, though lined by purple corium; the carinal half of the tergum pink. Walls extremely smooth. Largest specimen above one inch in basal diameter. _Scuta_, with the finest striæ radiating from the apex; growth-ridges moderately prominent; articular ridge small; there is a very slight and blunt adductor ridge: the hollow for the lateral depressor muscle is rather narrow and deep. _Terga_, with the apex slightly prominent or beaked; the longitudinal furrow is of very little depth; on its scutal margin there is a narrow, rounded, slightly prominent ridge, which, however, appears more like a furrow than a ridge. Spur moderately long and blunt; placed at half its own width from the basi-scutal angle; the basal margin on both sides of the spur, slopes gently towards it. Internally, the articular ridge is pretty well developed; the scutal margin is not much inflected; the carinal portion of the under surface of the valve is rough; the crests for the carinal depressor muscle are entirely absent.
_Compartments._--Walls moderately strong; parietal tubes small, with transverse septa in their upper ends; inner surface of the walls much less strongly ribbed than is usual. _Radii_ broad, with their summits parallel to the basis; their septa are strongly denticulated. _Alæ_ with their summits oblique; their sutural edges are barely crenated. _Basis_, thin, flat, or cup-formed. _Body_ unknown. _Affinities._--In general appearance this species comes near to _B. psittacus_; but in all essential characters it comes much closer to the following species, from which, however, it can easily be distinguished by colour, and by the inner lamina of the parietes not being cancellated. 7. BALANUS VINACEUS. Pl. 2, fig. 7 _a_-7 _d_. _Shell purplish dark brown: inner lamina of the parietes cancellated. Scutum finely striated longitudinally. Tergum with the longitudinal furrow shallow and open; basal margin on both sides sloping towards the spur._ _Hab._--West Coast of South America. Mus. Cuming. _General Appearance._--Shell conical, with a large, rhomboidal orifice; walls rather thin, coloured, together with the radii and operculum, dark purplish-brown; sheath nearly colourless. Walls smooth, slightly irregular, very finely striated longitudinally. Basal diameter of largest specimen .8 of an inch.
_Opercular Valves_, unusually smooth, that is without prominent growth-ridges. _Scuta_, finely striated longitudinally, with the sharp striæ closely approximate. The teeth on the occludent margin are sharp, and stand some way apart from each other. Internally, the whole surface is remarkably flat and smooth: the articular ridge is of moderate breadth, and slightly reflexed: there is no adductor ridge, and the oval depression for the lateral depressor muscle is extremely slight. _Terga_, with the longitudinal furrow very slight; the bottom of this furrow is feebly striated longitudinally, and there is a trace of a fine, rounded ridge on the scutal margin, as in _B. decorus_. The basal margin slopes on both sides towards the spur, which is of moderate length and breadth, with its lower end truncated and parallel to the carino-basal margin; the spur stands at about once and a half its own width from the basi-scutal angle. Internally, the valve is lined by very dark, purplish-brown corium; the articular ridge is prominent; in the upper part of the valve, parallel to the articular ridge, there are two or three feeble ridges; there are no crests for the tergal depressores.
The _Parietes_, though moderately thick, yet are light and fragile; the denticuli at the bases of the longitudinal septa are prominent, and those on the adjoining septa are united together, making a network (Pl. 2, fig. 7 _d_), but the interspaces between them are not filled up by solid calcareous matter (as is the case with every other species of the genus), but are only crossed at successive levels by fine transverse calcareous septa; the internal lamina thus becoming cancellated, and, though thick, fragile. Hence, in a transverse section of the parietes, the ordinary parietal tubes or pores are seen to be lined on their inner sides by five or six rows of very minute pores. I have not seen any other instance of this structure. The internal lamina is ribbed, as usual, on its inner surface, by the projection of the longitudinal septa. The ordinary parietal tubes are open, to nearly the summit of the shell. The _radii_ are rather thin, and unusually fragile; their summits are parallel to the basis: their septa, as seen on the sutural edges, are extremely thin and denticulated on both their upper and lower surfaces, on the side towards the internal lamina: towards the external lamina, the septa are simple, and the small square pores thus formed, are open or not filled up. The _alæ_ have their summits extremely oblique, being added to very little during the diametric growth of the shell; the narrow margin, however, which is thus added, is coloured red, the rest of the sheath being nearly colourless: the sutural edges of the alæ are smooth. The _basis_ has a thick, underlying, finely cancellated layer of shell.
_Animal's body_ unknown. A young specimen, .2 of an inch in basal diameter, differed from the above in being of a much paler purplish-brown. This species is distinct from all its congeners, in its peculiar colour, and likewise in the structure of the inner lamina of the parietes. As already stated, it comes nearer to _B. decorus_ than to any other species. 8. BALANUS AJAX. Pl. 3, fig. 1 _a_-1 _d_. BALANUS TINTINNABULUM (_var._) _Chenu._ Illust. Conch., Tab. 2, fig. 8. _Shell globulo-conical, often elongated in the rostro-carinal axis, pale pink, smooth, extremely massive: parietal pores, close to the basal margin, circular and very small. Scutum with the articular ridge broad and reflexed._ _Hab._--Philippine Archipelago, attached to _Millepora complanata_, Mus. Cuming. Mus. Brit. and Stutchbury. _General Appearance._--Shell globulo-convex, sometimes much elongated in its rostro-carinal axis; smooth; walls excessively strong, massive, and heavy. Orifice oval, rather small in proportion to the size of shell, this being chiefly due to the infolding of the upper part of the rostral compartment. Parietes pale pink, feebly tinted with purple: radii either paler, or tinted of a bright chesnut-brown: sheath rich purplish chesnut-brown. Basal diameter of the largest specimen nearly 3-1/2 of an inch; height 2-3/4: another specimen had a basal longitudinal diameter of 2.9 of an inch, and a transverse diameter of only 1.6; this great difference in the two diameters being caused by the prolongation of the basal portion of the rostrum in the line of the branch of the Millepora, to which the shell had adhered; the height of this same specimen was 1.5; and the diameter of the orifice, both transversely and longitudinally, .75 of an inch.
_Scuta_, broad, feebly tinted with pink; exterior surface rough, with sharp hood-formed projections, arranged in straight lines radiating from the apex; an inflected portion of the valve along the tergal margin is not roughened. Internally (Pl. 3, fig. 1 _d_), the articular ridge is broad and reflexed. An adductor ridge can hardly be said to exist, but a slight prominence borders the gentle hollow in which the lateral depressor muscle is attached. The basal margin, on its inner face, is slightly toothed. _Tergum_ white, with the narrow part of the valve, on the scutal side of the spur, rough with the little projecting hoods, like those on the scutum; the other and larger half is smooth: spur rather long, narrow, placed at twice its own width from the basi-scutal angle; on the carinal side, about half of the basal margin slopes down towards the spur. The longitudinal furrow is either quite or nearly closed. Internally, the spur is produced upwards on the valve, as a prominence: the articular ridge is not very prominent. There are no crests for the tergal depressor muscle. Altogether the opercular valves strikingly resemble those of _B. tintinnabulum_, but all the characters above mentioned have not been observed in any one variety of this species; perhaps _var. coccopoma_ comes nearest, both in the external appearance of the shell and in the structure of the opercular valves, to _B. Ajax_.
The _Compartments_ are remarkably compact and solid; the parietal tubes are cylindrical and quite minute even close to the basis; they extend, however, nearly up to the top of the shell; the parietal septa at the basis are thick, and with blunt denticuli; the thickness of the walls in the upper part of the shell is excessive; in the lower part, it is also unusually great, owing to the thickness of the inner lamina, and hence the ribs, generally formed by the projection of the longitudinal septa on the inner lamina, are here visible only close to the basis. The _radii_ are rather wide; their summits are parallel to the basis; the septa on their sutural edges are thin, straight, and closely approximate, and most symmetrically furnished with little denticuli of equal sizes on both sides: the interspaces are nearly filled up solidly, but with some pores still left open. In the upper part of the shell, the radii, like the walls, are of extraordinary thickness: the septa are transverse and horizontal, as seen externally by slight variations in the colour of the radii; internally, as seen in a vertical section of the shell, the septa dip inwards at an angle of above 45°. The _alæ_ are thin, and have their summits oblique: their sutural edges are smooth. The pores in the basis are crossed by numerous transverse septa, and there is an underlying cancellated layer: the internal surface is very smooth.
_Animal's body_ unknown. The strength of this Balanus is truly remarkable; and when, by repeated blows, a specimen which I was examining at last yielded, the radii broke sooner than separate at their sutures. In most of its characters, this species approaches _B. tintinnabulum_, and I believe has been included by Chenu as one of its varieties; but it comes almost equally near to _B. stultus_, to which it is much more closely allied in its habit of being attached to Milleporæ. By a close and unbroken chain of affinities, _B. Ajax_, through _B. stultus_, is connected with _B. calceolus_ and its allies in section (B), which live attached to Gorgoniæ. Some of the specimens of _B. Ajax_, are almost as much elongated in their rostro-carinal axis, as are the species in section (B); and there is an affinity in the same direction in the smallness of the pores in the radii of _B. Ajax_; indeed, had the basis in this species been generally more boat-or cup-formed, I should have placed it as the first species in section (B), instead of, as at present, the last species in section (A). The intermediateness of the characters of _B. Ajax_ has been one chief cause why I have rejected the genus Conopea, which was instituted by Say for the species living attached to Gorgoniæ.
_Section_ B. _Parietes and basis sometimes permeated by pores, sometimes not: radii not permeated by pores: shell elongated in its rostro-carinal axis: basis boat-shaped: attached to Gorgoniæ and Milleporæ._ 9. BALANUS STULTUS. Pl. 3, fig. 2 _a_-2 _d_. _Parietes and base porose: shell white, or faintly tinged with purple. Scutum with the basal margin protuberant in the middle. Tergum with the longitudinal furrow closed in the upper part: spur not closely adjoining the basi-scutal angle._ _Hab._--Attached to Milleporæ, Singapore, Mus. Cuming. West Indies,[89] Mus. Brit.--Mus. Stutchbury. [89] This specimen in the British Museum was purchased at the sale of the Rev. L. Guilding's collection, and therefore it is not certain that this habitat is correct; but as it was sold in the same lot with a Cirripede certainly West Indian, and as the main collection was made in the West Indies, this habitat may, I think, be trusted. I have considerable doubts whether it would not have been more correct to have placed this species in the last section, instead of where it now stands; it certainly is more closely allied to _B. Ajax_, especially in its operculum, than to the following species; yet the fact of the radii not being permeated by pores does not permit of its admission into the last section; and both in habits and structure it undoubtedly comes very near to the following species. Those varieties which are not much elongated, and which have the basis nearly flat, would certainly, if considered by themselves alone, not have gained admission into our present section.
_General Appearance._--Shell conical, somewhat globular, more or less elongated in the rostro-carinal axis, owing to the basal production of the rostrum. Orifice, rather small, entire, oval, pointed at the carinal end. Radii moderately broad, with their summits parallel to the basis. Colour dirty white, often faintly tinged with purple; sheath, pale purplish-blue. Surface extremely smooth; the parietes are generally covered (as viewed through a lens) by a very thin, yellowish epidermis, giving to the whole a glistening, granular aspect: the radii are generally destitute of this epidermis, and are therefore of a dead white. The basis is concave, and sometimes deeply cup-formed; it is, however, not symmetrical; sometimes it is flat. Basal diameter of largest specimen, including the basis itself, 1.5 of an inch in the longitudinal axis; transverse diameter, 1 inch; the inequality in the length of the two diameters is rarely so great as in this unusually large specimen. _Scuta_, externally very convex, with the growth-ridges extremely prominent; basal margin sinuous, the middle portion being prominent; this is best seen in young specimens (Pl. 3, fig. 2 _d_). Internally, the articular ridge is broad and reflexed. The adductor ridge in the upper part is almost confluent with the articular ridge; it runs down to the most prominent point of the basal margin; in young specimens it is sharp and prominent; in old specimens it is very blunt and little prominent. There is a rather deep hollow for the lateral depressor muscle. In young specimens there is a small, depending, blunt tooth at the basi-tergal angle, which helps to make the basal margin more deeply sinuous.
_Terga_, with the longitudinal furrow closed, except on the spur itself, where it is open. The spur is moderately long and broad, but varies in breadth; it is placed at rather less than its own width from the basi-scutal angle; its lower end is obliquely rounded; the basal margin on the opposite sides of the spur, together form a nearly straight line. The whole valve is rather broad. The crests for the tergal depressores are barely developed. The _Compartments_ have rather large parietal tubes; the septa are coarsely denticulated at their bases; the internal lamina is smooth, except close to the basis. The _radii_ have their summits parallel to the basis; their sutural edges are formed of rather thick septa, which stand at an unusual distance apart from each other, and have perfectly symmetrical, minute denticuli on each side. The interspaces between the septa are filled up solidly to within a short distance of the surface; but yet not so completely as in the following species, and as in those in the succeeding sections of the genus; this is what might have been expected from the close affinity of _B. stultus_ to _B. Ajax_, in which latter the radii are still permeated by pores, though smaller than is general in the species of our first section (A). The _alæ_ have their summits extremely oblique, and their sutural edges, I believe, smooth. _Basis_ porose, with an underlying, finely-cancellated layer.
_Mouth_: labrum with six small teeth; mandibles with the 3d tooth blunt; the 4th minute, and the 5th almost confluent with the inferior angle. Maxillæ with the edge straight and simple. _Cirri_ partly destroyed; on each segment of the sixth pair there were five pairs of spines. 10. BALANUS CALCEOLUS. Pl. 3, fig. 3 _a_-3 _e_. BALANUS CALCEOLUS KERATOPHYTO INVOLUTUS (?) _Ellis._ Phil. Trans., vol. 50 (1758), Tab. 34, fig. 19. LEPAS CALCEOLUS (?) _Pallas._ Elench. Zooph., p. 198, (sine descript.) (1766). CONOPEA OVATA (?) _J. E. Gray._ Annals of Philosophy, vol. x, 1825. _Parietes and basis porose. Scutum with the pit for the lateral depressor muscle small and deep._ _Hab._--Attached to Gorgoniæ, West Coast of Africa. Tubicoreen, near Madras, (Dr. Johnston), associated with _B. navicula_. Mediterranean (?). Mus. Brit., Cuming, Stutchbury. _Fossil._ Coralline Crag; Mus. S. Wood. I must premise, with respect to the nomenclature of this and the three following quite distinct species, that in the published descriptions no allusion is made to any one of the characters by which alone they can be distinguished: hence I have been guided by geographical probabilities in assigning the specific name of _calceolus_ to the present species, as Ellis's specimens came from the Mediterranean; and that of _galeatus_ to the North American and West Indian specimens, as Linnæus' original specimens (according to a statement by Spengler) came from the West Indies. I have assigned new names to the two remaining East Indian species. I may here add that Spengler ('Skrifter af Naturhist.' 1 B, tab. 6, fig. 3, 1790) has described, under the name of _B. cassis_, an allied form attached to the _Gorgonia placomus_ from the seas of Norway; but I do not believe that it is the same with our present species.
_General Appearance._--The degree of elongation of the shell in its rostro-carinal axis varies considerably (3 _a_, 3 _b_): the elongation is due to the production of the rostrum and of the corresponding end of the basal cup. These two portions of the shell always form together an angle, and sometimes an acute angle, whereas in all the many specimens which I have seen, the carina and the carinal end (or heel) of the basis together form a straight line; yet I should not be surprised if this end of the shell was sometimes produced. The surface of the shell is smooth, or sometimes marked with very minute projecting points: it is almost always covered by the horny bark of the Gorgonia. The colour is either dull purplish-red or dull purple, with obscure longitudinal stripes, and often more or less transversely banded with white. The rostrum is either white or very feebly tinted, being always paler than the rest of the shell: the radii are usually paler than the parietes, and are sometimes white: the carinal end of the basal cup is tinted of the same colour with, but rather paler than, the compartments. The orifice is rather small compared to the shell, and nearly heart-shaped. The carino-lateral compartments are about one-third of the width of the lateral compartments. The shell is very strong, and the sutures resist the action of boiling caustic potash. The largest specimen which I have seen was .7 of an inch in extreme length, and under .25 in extreme breadth.
_Structure of the shell and basis._--The parietes are permeated by quite distinct pores,--a character sufficient by itself to separate this from the following species; the longitudinal septa forming the tubes are slightly denticulated at their bases. The radii have their summits quite square, extending from apex to apex of the adjoining compartments. The alæ have oblique summits. The sutural edges of the radii have approximate septa, which are obscurely denticulated: the interspaces are filled up solidly, so that the radii are not porose. The basis is distinctly porose, by which this species can be distinguished from _B. navicula_ and _cymbiformis_. The basis has a deep furrow on the under side, from clasping the thin horny axis of the Gorgonia: the basal point of the rostrum is also notched from the same cause, and, as a consequence, its upper surface becomes slightly furrowed along its whole length. The _Scuta_ have an articular ridge but moderately prominent, and only slightly reflexed; the basi-tergal corner is rounded off; there is no adductor ridge; there is a small, rather deep, distinct pit for the lateral depressor muscle. _Terga_; externally the surface is considerably depressed in the line of the spur. The spur is between half and one-third of the width of the valve: its lower end is square and truncated, or in some degree rounded; it is sometimes (3 _e_) dentated with a few, minute, sharp teeth. The articular ridge is but slightly developed; the crests for the depressor muscle are very feeble.
Text from Project Gutenberg, public domain in the United States.