A Monograph on the Sub-class Cirripedia · Charles Darwin
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_Scuta._--The scuta and carinal half of the terga are blueish-green. In the scuta neither the articular ridge or furrow are much developed: the adductor ridge is prominent, and is united to the articular ridge, about half way up the latter, thus forming a rather large, triangular cavity, which runs up to the apex of the valve. The _Terga_ are beaked. The spur, measured across the upper part, is half as wide as the valve; it is bluntly pointed; it is placed quite close to the basi-scutal angle of the valve, so that there is no basal margin on that side; it curves towards the scutum, its extremity extending beyond the basi-scutal angle. _Structure of the Shell and Radii._--The parietal tubes are rather large, especially those adjoining the inner lamina of the walls. The shell is of singularly little specific gravity, which is due to the parietal tubes not being filled up with shelly matter nearly to so great an extent as in the other species; even in the uppermost part the tubes are not solidly filled up, only their external sides are thickly coated with greenish-black shell, which by corrosion becomes grayish. The radii, as stated, are not developed: the shell breaks with singular facility along the sutures, and the radii are then seen to be most feebly represented by a few very small branching ridges. The alæ have their edges plainly crenated. The sheath is dark green, with the lower edge free.
The _Mouth_ presents no particular characters. With regard to the _Cirri_, I am doubtful whether any confidence can be placed in the numbers of the segments being constant; but I may state that the second cirrus contained thirteen and sixteen segments in its two rami; the third cirrus only fourteen in both rami; and the sixth cirrus twenty-six segments in both rami. Whereas in every specimen of _T. porosa_, the longer ramus of the third cirrus contained more segments than either ramus of the second. About half the segments, namely, those in the middle of both rami of the third cirrus, are furnished with coarsely and doubly pectinated spines, like those in _T. porosa_. _Affinities._--Upon the whole, this species is more nearly allied to _T. porosa_ than to any other. In the cavity formed by the union of the adductor and articular ridges, it is allied to _T. cœrulescens_. This species differs from all, in its little specific gravity, consequent on the parietal tubes being only slightly filled up, and in the peculiarly serrated, narrow, approximate ridges on the external surface of the walls. The character derived from the adductor ridge, just alluded to, is remarkable. In the shape of the terga, in the absence of radii, and in the structure of the body, this species approaches closely to _T. porosa_.
3. TETRACLITA ROSEA. Pl. 10, fig. 3 _a_-3 _d_. CONIA ROSEA.[109] _Krauss_ (!). Die Südafrikanischen Mollusken, Tab. 6, fig. 28, 1848. BALANUS CUMINGII. _Chenu._ Illust. Conch., Tab. 4, fig. 5. [109] I am greatly indebted to Professor Krauss for having sent me, for examination, the unique specimen collected by himself in Algoa Bay. There can be no doubt of the identity of the African and Australian specimens. It is a singular circumstance that the same species should occur in these two distant places, and, as far as at present known, not in the intermediate, more tropical coasts. _Shell dirty white, tinged with pink; parietes formed by a single row of large tubes: radii generally narrow: tergum with the spur rather short and broad._ _Hab._--New South Wales, Moreton Bay in lat. 27°, Port Jackson, and Twofold Bay; South Africa, Algoa Bay. Attached, in Australia, to littoral rocks and shells; often associated with _T. purpurascens_, _Chthamalus antennatus_, and _Catophragmus polymerus_; Mus. Brit., Cuming, Krauss, Darwin, Stutchbury.
_General Appearance._--Shell steeply conical, often rather convex; dirty or brownish white, feebly tinted with pink; external surface generally much disintegrated, and having in the upper part a pillared appearance, owing to the exposure of the upfilled, large, square, parietal tubes, and, in the lower part, a striated (and sometimes serrated) appearance, from the exposure of the parallel, approximate plates, with which the outer lamina of the shell is internally strengthened. In only a few young specimens, the whole outer lamina of the shell was well preserved; and in these the surface was very smooth, and even glossy, giving to the specimens a quite different aspect; even in partially corroded specimens, the lower part of the shell sometimes is quite smooth. Generally, the radii are developed; in most specimens they are narrow, but sometimes of moderate width; their summits are oblique, and their edges often notched or toothed. The recipient furrow, in each opposed compartment, is often almost as wide as the radius itself, and is equally notched. In some much corroded specimens there were no radii. Basal diameter of largest specimen, 1.1 of an inch. _Scuta_, generally thick, sometimes very thick, with the external surface usually much corroded: articular furrow rather wide; articular ridge not very prominent; adductor ridge prominent. The rostral depressor muscle is attached in a small oblong pit, sometimes including little crests; and the lateral depressor muscle is attached to what may be described either as three or four parallel furrows or crests.
_Terga_, with the spur placed close to the basi-scutal angle, so that there is no basal margin on that side; spur short, with its lower end truncated and rounded; broad, even exceeding, when measured across the upper part, half the width of the valve. Articular furrow wide. Apex not beaked. _Structure of Walls and Radii._--This species differs from all the others of the genus in having only a single row (fig. 3 _d_) of parietal tubes; these are large, quadrangular, but elongated in the ray of the circle. They are not filled up, even at the very top of the shell, but they become thickly lined all round with compact shelly matter. When the surface of the shell is disintegrated, these upfilled tubes greatly affect, as already stated, the external appearance. The outer lamina near the basis is internally strengthened by longitudinal, sharp, approximate ridges or plates, which, also, often affect, after corrosion, the external appearance. The _radii_ have their sutural edges formed by a set of narrow, branching ridges or septa; the ends of which, seen externally, often give a notched outline to this edge; the recipient furrows in the opposed compartments are deep, and their edges likewise are often notched: the interspaces between the branching ridges are filled up solidly. The _alæ_ have their edges coarsely crenated. The lower edge of the sheath is not free.
The _mouth_ and _cirri_ present no particular characters: the third cirrus has both its rami elongated, with the terminal segment tapering. In the three posterior pairs of cirri, the tufts of little spines between the main pairs are rather large. _Affinities._--This species has no particular affinity with any other. The circumstance of there being only a single row of parietal tubes is not so important a difference as might at first be thought, inasmuch as in the other species, during their quite early youth, the walls are formed of only a single row of tubes or pores. 4. TETRACLITA PURPURASCENS. Pl. 11, fig. 1 _a_-1 _d_. LEPAS PURPURASCENS.[110] _Wood's_ General Conchology, p. 55, Pl. 9, fig. 42, 1815. BALANUS PLICATUS. _Lamarck._ Animaux sans Vertèbres, 1818. ---- ---- ET PUNCTURATUS. _Chenu._ Illust. Conch., Tab. 4, fig. 3 et 12. CONIA DEPRESSA (!). _J. E. Gray._ Appendix, Dieffenbach's Travels in New Zealand, 1843 (sine descript. vel figurâ). [110] The descriptions given by Wood and Lamarck are fuller and more accurate than is usual in the case of Cirripedes, and I have no doubt regarding these two names. The _Conia depressa_ of Dr. J. E. Gray is, as I know from having seen the original specimens, the young of this same species; the name is unaccompanied by any description or figure. _Shell depressed, pale purple or dirty white, with the surface longitudinally ribbed, or corroded and granulated: radii or even sutures none, or radii well developed and broad, with their summits parallel to the basis: basis membranous: scutum transversely elongated: tergum small, with the spur extremely short and rounded._
_Hab._--Sydney, New South Wales; Flinder's Lagoon, Sir C. Hardy's Island, Barrier Reef; King George's Sound, Western Australia; Van Diemen's Land; New Zealand, adhering to _Pollicipes spinosus_; Mus. Brit., Cuming, Stutchbury, Darwin, &c. China (?) attached to _Pollicipes mitella_, Mus. Brit. and Stutchbury. Generally attached to tidal rocks, sometimes to shells. Very common. _General Appearance._--Shell generally much depressed, in a few cases rather steeply conical, in one single instance cylindrical, but not much elongated. Colour, when alive, pale, but fine purple; I presume, judging from some dried specimens, sometimes dirty white. The state of the surface varies remarkably: about half the specimens (fig. 1 _a_) which I have seen, had the outer lamina of shell quite removed, and the surface granulated, owing to the projecting and exposed tips of the upfilled parietal tubes; the radii are not developed, and often even there is no trace of the four sutures; the rather large orifice is somewhat rounded, and the two scuta, with their surfaces disintegrated, have their middle parts deeply indenting the terga. The shell, in the other and perhaps more common condition (fig. 1 _b_), has the outer lamina preserved, and is longitudinally ribbed with generally at least five or six ribs on each compartment: the radii are here very wide, and extend from tip to tip of the compartments, so that their summits are parallel to the basis; they are generally covered by a brownish epidermis, thickly clothed with little spines; the orifice is neatly diamond-shaped; the apices of the opercular valves meet at a common point: these specimens are almost always smaller and younger than the granulated specimens. Altogether the specimens in the two opposite states have, in their external appearance, nothing in common, and no one, without careful examination, would ever suspect that they were specifically identical; this, however, was proved by the intermediate forms, and, in one instance, three of the compartments had their surfaces granulated, and were entirely destitute of the radii, whilst the fourth by some chance had been preserved from corrosion, was longitudinally ribbed, and had its epidermis-covered radius fully developed. The difference in the appearance of the opercular valves, in the two states, is simply owing to the degradation of their upper parts in the granulated specimens.
The basal diameter of the largest specimen was one inch, but the height only .35 of an inch. _Scuta_, transversely elongated, so that the basal margin is nearly twice as long as the tergal margin: articular ridge very little prominent; articular furrow wide but shallow; adductor ridge very blunt, slightly prominent, sometimes almost absent, almost parallel to the basal margin: there are no distinct crests for the rostral or lateral depressor muscles, but some small irregular pits for the latter. In one young specimen, the lines of growth were crenated, showing a tendency in the valve to become longitudinally striated, as in the allied _T. costata_. In some young and immature specimens, the basal margin was deeply sinuous. _Terga_, small in area, not above half that of the scuta: spur extremely short, broad, placed close to the basi-scutal angle of the valve, so that there is no basal margin on that side of the spur. The lower end and sides of the spur form one uniform curve. Articular ridge barely developed. Crests for the tergal depressores sharp and prominent.
_Structure of the Shell and Radii._--The walls are very thick, and the parietal tubes small and numerous; there are sometimes from twelve to fifteen rows of tubes in the thickness of the wall. The tubes in their whole upper part are filled up solidly; and, as we have seen, are often exposed by disintegration. In very young specimens, of that size in which in _T. porosa_ there would be only a single row of parietal tubes, there were here two or three rows. The development of the radii, as we have seen, is very capricious; the sutures even sometimes being lost. The radii, when developed, are broad, square on the summit, and covered by brownish hirsute epidermis: internally they are formed of tubes like those forming the parietes; in this respect differing from all the species except the following, _T. costata_. The tubes in the radii run obliquely down towards the basis; instead of in a transverse line, directly towards the opposite compartment, as might have been expected from the structure of the radii in Balanus. The alæ have their edges finely crenated. The sheath in all the specimens which I have observed is colourless; its lower edge is not free. The corium entering the parietal tubes, and lining the opercular valves, the mouth, and the anterior cirri, is generally of an extremely dark purple colour.
The _Basis_ is entirely membranous, in which respect this species differs from all the others in the genus. _Mouth_: all the trophi are unusually hairy or spinose. The labrum is deeply notched and apparently destitute of teeth on the crest. The palpi are club-shaped or enlarged at their extremities. The mandibles have the fourth tooth rudimentary. In the _Cirri_, the second and third pairs are remarkably short and blunt. In one specimen the two rami of the first cirrus had respectively six and sixteen segments; those of the second, six and seven; those of the third, seven and seven; and those of the sixth cirrus twenty rather elongated segments, with a small tuft of spines between each main pair of spines. _Affinities._--This species differs from all, in its membranous basis, and in its transversely elongated scuta. It resembles _T. costata_, and differs from all the other species, in its radii (when developed) being square on the summit, and in being formed of tubes,--in the smallness and number of the parietal tubes,--in the absence of crests on the under side of the scuta for the rostral and lateral depressor muscles,--in the shortness and rounded form of the spur to the terga,--and, lastly, in the club-shaped palpi and small size or absence of the fourth tooth in the mandibles. _T. purpurascens_ differs from _T. costata_ in those points, namely, in its membranous basis and transversely elongated scuta, in which it differs from all the other species, and, moreover, in its scuta not being plainly striated longitudinally, in having more ribs on the external surface of the parietes of its shell, and in having only three pairs of main spines on the three posterior cirri.
5. TETRACLITA COSTATA. Pl. 11, fig. 2 _a_-2 _c_. _Shell depressed, whitish, generally with ten very prominent longitudinal ribs: radii broad, with their summits parallel to the basis: basis calcareous: scutum externally striated longitudinally: tergum with the spur short and rounded._ _Hab._--Philippine Archipelago, Mus. Cuming. Attached to various shells, within the tidal limit. _General Appearance._--Shell whitish, probably tinged, when alive, with reddish-purple; depressed; surface perfectly preserved, smooth, but having longitudinal very prominent ribs, almost invariably ten in number; namely, three on both the rostrum and carina, and two on the two lateral compartments, with ten corresponding projections round the basal margin. Orifice passing from rounded-trigonal to diamond-shaped. The radii are very broad and square at the summit, and extend from tip to tip of the compartments. Basal diameter of largest specimen under half an inch, generally from .3 to .4 of an inch. _Scuta_, of the usual sub-triangular shape, and not transversely elongated, as in _T. purpurascens_. External surface striated longitudinally; in many specimens there is a medial depression, or a row of very small pits, such as occur on the scuta of _Balanus trigonus_ and _lævis_. The adductor ridge is moderately developed, and runs nearly parallel to the occludent margin; there are no crests for the rostral and lateral depressor muscles. _Terga_: these in area equal two thirds of the scuta: the spur is short and rounded, and placed as described under _T. purpurascens_; but the articular ridge seems to be more prominent than in that species.
_Structure of the Shell and Radii._--The parietal tubes are small, and very numerous, as in _T. purpurascens_. The radii are wide, square on the summits, but not so conspicuously covered by hirsute epidermis as in that species. Internally, the tubes forming the radii are smaller, and run more transversely than in _T. purpurascens_, that is in the normal course, as in Balanus. The edges of the alæ are nearly or quite smooth. The _Basis_ is as distinctly calcareous, as in the other species of the genus. _Mouth_: the trophi are not so hairy as in _T. purpurascens_; the labrum seems destitute of teeth; the palpi are club-shaped at their ends; the mandibles have only three teeth. The second and third cirri are not so short and blunt relatively to the others as in _T. purpurascens_. In the posterior cirri, the elongated segments carry four main pairs of spines, between which there is no intermediate tuft of fine spines. The _Affinities_ of this species have been fully pointed out under the last and closely related species. In external appearance, _T. costata_ can at first hardly be distinguished from those young and pale-coloured varieties of _T. purpurascens_, which have their external surface not corroded, and their radii well developed. 6. TETRACLITA VITIATA. Pl. 11, fig. 3 _a_-3 _e_. _Shell white, generally tinged in the upper part with pink; surface irregular: parietal tubes very irregular: radii moderately wide, with their summits oblique: alæ with very thick crenated sutural edges: tergum with the spur not joined to the basi-scutal angle; spur with its extremity equably rounded._
_Hab._--Philippine Archipelago; Barrier Reef, (Raine's Islet), Australia; Mus. Cuming and Stutchbury. Attached to massive corals, to coral-rock, to a Tridacna, and to _Tetraclita cœrulescens_. _General Appearance._--Shell conical, moderately steep: white, generally with a tinge of pinkish-purple in the upper part, owing to the exposure of the tips of the upfilled parietal tubes. The lower part of the surface is generally well preserved, and is formed by very irregular, branching, longitudinal, slightly prominent, ridges. Radii of moderate width, with their summits oblique. Orifice rather large, rounded trigonal. _Scuta_, rather narrow, with the upper part acuminated: the external surface generally much disintegrated, and marked with some irregular blotches of dark red. Articular ridge not prominent; articular furrow rather deep: adductor ridge, distinct from the articular ridge, pretty well developed, as are the crests for the rostral and lateral depressor muscles. In young and well preserved scuta, there is an external, medial, hyaline band, corresponding with the hollow under the adductor ridge, and caused by the thinness of the valve along this line. _Terga_: externally, the carinal half is longitudinally and very feebly striated. Internally, the articular furrow is very wide, but shallow, and of unusual length, owing to the preservation of the upper part of the valve; the articular ridge is not prominent. The spur does not actually join, as in all the foregoing species, the basi-scutal angle, but is separated from it by a short piece of basal margin; its two sides are more nearly parallel than is usual, and the end is regularly rounded. It is always rather narrow, though the width varies considerably (fig. 3 _d_, 3 _e_). It extends in the same straight line with the middle of the articular furrow. The terga, though not possessing any striking characters, differ considerably in appearance from those of the other species.
_Structure of the Shell and Radii._--The parietal tubes are remarkable from their irregular shapes, and unequal sizes (fig. 3 _b_),--hardly two resembling each other. Sometimes a single elongated tube will reach across the whole thickness of the walls. The septa between the tubes are rather thick and rugged. The tubes are generally darkly coloured from the adhering corium; they are solidly upfilled, but only in the uppermost part, by dark chocolate-red shelly matter. The radii are formed by irregularly branching ridges, with the interspaces filled up solidly. The square edges of the alæ are much thicker than in any other species, and are furnished with transverse ridges, which are sometimes slightly branched. The inner lamina of the walls near the basis, in most of the specimens, is irregularly and longitudinally ribbed, the ribs being longitudinally striated. The sheath and the upper part of the inner lamina of the parietes are clouded with chocolate-red. The animal's _Mouth_ and _Cirri_ were ill-preserved; but I was able to make out that the labrum had some strong teeth, and that the mandibles were furnished with five teeth, a greater number than in any other species. The palpi had parallel sides as usual. In the sixth cirrus, the segments had four pairs of main spines, instead of the usual number of three. _Affinities._--This species does not appear to be particularly related to any other one: perhaps it is rather nearer to the two following than to the foregoing species. The irregular parietal tubes, thick-edged alæ, form of terga, five teeth to the mandibles, and four pairs of spines to the segments of the posterior cirri, are its chief characteristics.
7. TETRACLITA CŒRULESCENS. Pl. 11, fig. 4 _a_-4 _d_. LEPAS CŒRULESCENS. _Spengler._ Skrivter af Selskabet, 1 Bind., 1790.[111] [111] The longitudinally folded walls, as described by Spengler, the blue colour, the habitat, namely, associated with _B. tintinnabulum_ from the East Indies, and more especially the expression "Valvulæ operculi cardine dentato mobilis," apparently referring to the highly prominent articular ridge of the scutum, leave little doubt on my mind that I have rightly named the present species. _Shell with the upper part tinged greenish-blue, longitudinally ribbed: radii moderately wide, with their summits oblique: scutum with a small adductor and extremely prominent articular ridge, united together and so forming a small sub-cylindrical cavity: tergum with the spur not joined to the basi-scutal angle._ _Hab._--Philippine Archipelago, attached to _Balanus tintinnabulum_; attached to a ship's bottom, and to _Balanus tintinnabulum_, both from the Pacific Ocean; attached to a massive coral, and associated with _T. vitiata_, and therefore from the tropical eastern seas; Mus. Brit., Cuming, Stutchbury. _General Appearance._--Shell conical, sometimes depressed; surface with rather broad, smooth, longitudinal ridges; whitish, with the upper part greenish-blue, sometimes very feebly tinted with pink; radii white, or mottled with blueish-green, or with pink. When the outer lamina of shell has been corroded, the upfilled parietal tubes, of a dull blueish-gray colour, are exposed. The radii are moderately wide, with their summits very oblique. In basal diameter, one specimen was 1.8, and another 1.5 of an inch.
_Scuta_, externally furrowed very slightly in a longitudinal direction, causing the lines of growth to become a little sinuous. The valve is strong and thick; and the epidermis, when preserved, is hirsute with spines. The articular ridge is extraordinarily prominent; it projects, as measured from the external surface of the valve, to an amount equalling half the width of the valve in its widest part. The adductor ridge is very short, and is united to the bottom of the articular ridge, thus forming a small, nearly cylindrical tube, which runs up to near the apex of the valve. The inflected occludent margin is broad and coarsely toothed. The crests for both depressor muscles are not very prominent. When the scuta and terga are articulated together, owing to the great projection of the articular ridge of the scutum, its upper part is separated from the tergum (fig. 4 _b_), by a remarkably wide and deep, fissure-like hollow. The scutum, in some distorted specimens from a ship's bottom, was narrow in proportion to its ordinary breadth. _Terga._--These are large. Externally, there is a broad, longitudinal depression, bounded on each side by a ridge. The carinal half is feebly striated longitudinally. A large upper portion (fig. 4 _b_) projects freely, and stands, when the two valves are articulated together, above the apex of the scutum, but does not form a beak as in _T. porosa_. Internally, the tergal margin is widely inflected; the articular furrow is very deep, but the articular ridge is not prominent. The spur is not very broad; it is separated from the basi-scutal angle by a small space of basal margin, which forms a straight line with the basal margin on the opposite side of the spur. The end of the spur is truncated, and is parallel to the basal margin.
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